The genetic and environmental basis of fruitfulness and growth of loblolly pines

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Title:
The genetic and environmental basis of fruitfulness and growth of loblolly pines
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v, 104 leaves : ill. ; 28 cm.
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English
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Schmidtling, Ronald Carl, 1937-
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Loblolly pine   ( lcsh )
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Thesis:
Thesis--University of Florida.
Bibliography:
Includes bibliographical references (leaves 95-103).
Statement of Responsibility:
by Ronald Carl Schmidtling.
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Typescript.
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Vita.

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University of Florida
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THE GENETIC AND ENVIRONMENTAL BASIS OF
FRUITFULNESS AND GROWTH IN LOBLOLLY PINES















By

RONALD CARL SCHMIDTLING


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY









UNIVERSITY OF FLORIDA


1980














ACKNOWLEDGEMENTS


I am indebted to Dr. Ray Goddard, chairman of my graduate

committee, for his many suggestions and reviews of the manuscript.

I am also appreciative for the help I received from the other

members of my graduate committee, Drs. A. E. Squillace, Charles

Hollis, E. S. Horner, and W. L. Pritchett, for their helpful

reviews.

I also gratefully acknowledge help I have received from U.S.

Forest Service research technicians Norm Scarbrough, Horace Smith,

Herschel Loper, and Victor Davis. Sincere appreciation is also

extended to past and present tree improvement personnel of the

Southern Region of the U.S. Forest Service, Johnsey King, Will

Schowalter, and Jim McConnell.














TABLE OF CONTENTS


PAGE

ACKNOWLEDGEMENTS ii

ABSTRACT iv

SECTION.

I GENETIC AND ENVIRONMENTAL VARIATION IN
FRUITFULNESS IN A LOBLOLLY PINE SEED ORCHARD..... 1

Introduction................................. 1
Literature Review............................ 2
Genotypic Variation..................... 3
Environmental Variation................... 5
Materials and Methods......................... 11
Results and Discussion....................... 16
Genetic Variation.......................... 16
Environmental Variation................... 41
Conclusions.................................. 61
Genetic Variation......................... 61
Environmental Variation.................... 63

II INHERITANCE OF PRECOCITY IN LOBLOLLY PINE
AND ITS RELATION TO GROWTH....................... 65

Literature Review............................ 66
Materials and Methods......................... 70
Results and Discussion....................... 76
Conclusions.................................. 90

SUMMARY AND CONCLUSIONS.......................... 92

Genetic Variability........................... 92
Environmental Variability.................... 93

LITERATURE CITED................................. 95

BIOGRAPHICAL SKETCH..............................104









Abstract of Dissertation Presented to the Graduate Council of the
University of Florida in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy


THE GENETIC AND ENVIRONMENTAL BASIS OF
FRUITFULNESS AND GROWTH IN LOBLOLLY PINES

By

Ronald Carl Schmidtling

June, 1980

Chairman: Ray E. Goddard
Major Department: Forest Resources and Conservation

Genetic and environmental variation in fruitfulness in loblolly

pines (Pinus taeda L.) were examined in clones and seedlings.

In a young loblolly pine seed orchard in south Mississippi clonal

variation was substantial. Over 50% of the variation in female flower-

ing, cone production, and seed production, and about 40% of the variation

in male flowering was attributable to genetic effects. The broad-sense

heritability for female flowering varied over time, however, increasing

at first to about 0.6 at 8 years of age and declining thereafter. The

decrease in heritability was mainly due to a large increase in environ-

mental variation after the 8th year.

Although the more fruitful clones tended to be fruitful every year,

significant year x clone interactions were found. The top 20% of seed

producing clones was not the same every year. Year x clone interactions

in male flowering also indicated that the genetic makeup of seeds collect-

ed from year to year may vary considerably, even if collected separately

by clone.









Flowering was inversely related to height and diameter growth, as

flowering was best on soils where growth was poorest. Yearly variation

in flowering also could be related to moisture stress, as a drought

during the strobilus initiation period seemed to favor abundant flower-

ing the following year. This was true of male as well as female

flowering, but the response to drought differed with respect to timing.

Male flowering was favored by an early summer drought (May-June) and

female flowering was favored by a late summer drought (July-August). It

was proposed that moisture stress exerts its effect by causing a cessa-

tion of vegetative growth coinciding with the time of flower induction,

thus allowing floral initials to form.

Genetic variation in average amount of flowering was very strong

among families in a diallel, and most of the variation was additive.

Diallel analysis and parent-progeny regressions yielded narrow-sense

heritability estimates of 0.61 and 0.52, respectively. The inheritance

in flowering at age 2, or precocity, was not as strong as that of

average flowering, being only 0.13 on an individual basis and 0.47 on

a family basis. Flowering traits were negatively correlated with growth

traits, indicating that selection for average flowering or precocity

alone would result in some growth loss. The results of a half-sib

progeny test incorporating precocious individuals, however, indicated

that selection for both precocity and growth could be profitable.














SECTION I

GENETIC AND ENVIRONMENTAL VARIATION IN FRUITFULNESS IN A
LOBLOLLY PINE SEED ORCHARD

Introduction

The goal of any tree improvement program is the production of

genetically superior trees. At present, southern pine plantations

are established with seedlings (rather than vegetative propagules);

and the tree improvement method commonly used is to establish clonal

seed orchards by grafting scions from phenotypically superior trees

onto seedling rootstocks. Traits such as growth, form, and quality

of the parent trees selected for the production of seed in either

type of orchard, clonal or seedlings, are of prime importance. How-

ever, fruitfulness also is important because the selections or their

progeny need to produce seed in sufficient quantities for the tree

improvement program to be successful.

A related factor influencing seed quality is pollen production

of the orchard trees. Breeders assume that most of the pollen effect-

ing fertilization in orchards will originate within the orchard. If

not, the realized genetic gain will be greatly reduced. Very little

is known about pollen production, for a major part of genetics research

has been done on female flowering and seed production. Although it

has been assumed that pollen from within the orchard will be adequate

for good pollination, this has not been so in many cases, perhaps

because conditions which were optimum for seed production may not have










been optimum for pollen production. Very small amounts of pollen are

required for controlled crosses in progeny tests. Often even these

small quantities are unavailable from some clones, making completion

of progeny tests very difficult.

Thus a major problem in tree improvement programs is the develop-

ment of an understanding of the inherent and environmental conditions

contributing to variation in flowering, pollination, and seed produc-

tion in southern pine orchards.

Flowering and seed yield data collected from a loblolly pine (Pinus

taeda L.) seed orchard over a period of several years were examined in

this report. The objectives of the study were to:

1. determine the extent of genetic control of male and female

flowering and their intercorrelations;

2. determine the year-to-year consistency of clonal differences

in flowering to evaluate the importance of yearly variation

in genetic worth of the seed produced and to examine the pre-

dictive value of early flowering data;

3. examine environmental variation in flowering and its relation-

ship to growth, to provide information on suitable conditions

for optimizing orchard output.

Literature Review

The emphasis of this review is on genetic and environmental effects

on flowering in conifers from an applied point of view. The role of

growth regulators, especially gibberellins (Pharis 1976), is surely

important, because they probably play a central role in floral initia-

tion, but is not directly pertinent to this research report.









Genotvyi: Variation

IT is generally recognized that large differences exist in fruit-

fulness between southern pine clones. This is considered a serious

problem in seed production since often only a few clones in an orchard

produce most of the seed. Bergman (1968) estimated that 2 of 15 clones

produced over half of the seed in a loblolly pine orchard. Others

estimated that 20% of the clones produced 80% of the seed (N.C. State

University 1976). A less pessimistic estimate was provided by Beers

(1974) who found that the top 20% of clones in seed production produced

56% of the seed in a slash pine (P. elliottii Engelm.) orchard.

Danbury (1971) estimated that seed production could be increased by 50%

and seed cost reduced by one-third if only the most productive half of

the clones available in a radiata pine (P. radiata D. Don) seed

orchard in Australia were retained. He assumed that growth and fruitful-

ness were weakly, if at all, correlated genetically. Inherent fruitfulness

can be especially important, since as a general rule trees which are

inherently unfruitful do not respond as well to treatments as do fruitful

trees (Bergman 1968).

The inherent ability of the individual tree to flower is probably

the most important factor influencing fruitfulness (Schmidtling 1974,

Shoulders 1967). It is important to consider this variation in the

design of experiments. In several fertilizer experiments, from 33%

(Schmidtling 1974) to 56% (Schmidtling 1975) of the total variation in

fruitfulness was attributable to clonal effects, even though the treat-

ment effects were large and significant. Broad-sense heritability










estimates for fruitfulness of 0.50 for slash pine (Varnell et al. 1967)

and 0.4 to 0.7 for loblolly pine (Schmidtling 1974) reinforced this

observation.

There is a general consensus that inherent variation in male

flowering is also large, but the effects seldom are quantified. Male

strobilus production is more difficult to measure than female, because

pollen catkins do not persist after pollen is shed and counts must be

timely. They are also relatively numerous, and thus costly to count.

Barnes and Bengtson (1968) and Schultz (1971) found strong clonal effects

on male flowering in a slash pine fertilization and irrigation study.

Webster (1974) also observed strong clonal effects on male flowering

in a loblolly pine orchard.

Most studies have shown that male and female flowering were not

closely related. Stern and Gregarius (1972) found that the correlation

between male and female flowering was very weak. Schultz (1971) found

a slightly negative genetic correlation between male and female flower-

ing in slash pine. This weak relationship between male and female

flowering is an important consideration in seed orchard management. If

we follow Danbury's (1971) suggestion and rogue 50% of the clones on

the basis of seed production, we might very well eliminate some of the

best pollen producers in the orchard, subsequently narrowing the genetic

base and perhaps eliminating some of the better genotypes.

The physiological basis for genetic differences has not been

determined, though Smith and Stanley (1967) showed that high cone

producing trees had higher N concentrations in needles than low cone










producers in response to N fertilizers. Considering all the observed

genotype x treatment interactions, a simple explanation does not seem

warranted. In general, the better flowering trees responded well to

fertilizers and the poorer trees responded poorly or not at all

(Bergman 1968, Schmidtling 1974, 1975). Deviations from this have

been noted. In addition to the kinds of response noted above, it has

been observed that some relatively unfruitful trees responded well to

fertilizers and some very fruitful trees did not (Schmidtling 1974, 1975).

Beers (1974) noted large differences among clones in response to level

of fertilizer, which lead him to suggest that individual clones should

be fertilized on a "prescription" basis. It appears that the limiting

physiological factor for flowering might differ considerably by genotype.

Environmental Variation

A large volume of literature exists that relates fruitfulness in

conifers to environmental variables (primarily those induced by experi-

mental means). Reviews by Jackson and Sweet (1972) and Puritch (1972)

give comprehensive coverage of the literature up to 1972.

The complex nature of the relationship between environmental

variation, either natural or induced, and flowering is clearly evident

in these reviews and in subsequent work. Many conditions or treatments

which promote flowering in conifers are those which promote the overall

growth and vigor of the tree, such as fertilization, thinning, and

increased insolation. On the other hand, treatments such as girdling,

moisture stress, root pruning or restriction, and poor mineral nutrition

which are detrimental to growth and vigor also promote flowering.










The greatest amount of research deals with fertilization and

mineral nutrition and their relationships to flowering. Management

plans for all southern pine seed orchards now include fertilization,

especially with N, as it is assumed that this will be necessary to

induce and maintain high levels of seed production. This assumption

has a sound basis in past research.

Puritch (1972) tabulated 25 references in which fertilizers were

applied to conifers. In all but three, fertilizers stimulated female

strobilus production. All 22 of the successful experiments included N

in the fertilizer. Nitrogen appeared to be the key fertilizer component.

An impressive number of studies showed a positive response to N alone

(Smith et al. 1968, Hoist 1959, Barnes and Bengston 1968, Cayford and

Jarvis 1967, Stephens 1961, Giertych and Forward 1966, Schultz 1971,

Ebell 1967, 1972, Morris and Beers 1969, Stoate et al. 1961, Barnes

1969, Goddard and Strickland 1966, Kraus 1925, Beers 1974).

Relatively few experiments distinguished the effects of each com-

ponent in fertilizer combinations of N, P, and K; and research on

nutrients other than these three has been lacking. In an NPK factorial

experiment with slash pine, Morris and Beers (1969) found that only N

stimulated flowering. Similarly, Goddard and Strickland (1966) reported

that N was of great importance, but that P and K also had some effect

when combined with N. Phosphorous and K applied without N, however,

depressed flowering. In an N-P factorial test conducted in a loblolly

pine seed orchard, ammonium nitrate tripled female strobilus production,

P had no effect, and the N + P treatment produced the same number of

female strobili as N alone (Schmidtling 1975). On the other hand,









Giertych (1973) observed that only K, in an NPK factorial, stimulated

female strobilus production in Scots pine (P. sylvestris L.). In

1968, van Buijtenen reported that P increased flowering in loblolly

pines and that N alone or in combination with P actually depressed

flowering. Although fertilization research has strongly supported a

positive role for N, under some conditions other nutrients may be

important.

Analyses of tissue N in conifers also has demonstrated a positive

role for N in flowering. Smith and Stanley (1967) and Smith et al.

(1968) found that good cone producers had a higher proportion of N

in their foliage than poor cone producers. Barnes and Bengston (1968)

showed that fertilizing with ammonium nitrate, which doubled female

flowering, increased N content, free arginine, and total amino acids

in twigs. However, N content per se may not be important. Ebell and

McMullan (1970) found that nitrate N and ammonium N increased foliar N

content and shoot growth in Douglas-fir (Pseudotsuga menziesii [Mirb.]

Franco) by similar amounts, but only nitrate-N increased female flower

production. Free arginine content was greater in nitrate-treated trees

than in the others and appeared to be quantitatively associated with

increased flower production.

In contrast to the voluminous research that showed increased

flowering related to fertilization and nitrogen content, several reports

have related nutrient deficiencies to enhanced flowering. Lyr and Hoffman

(1964) were able to induce flowering in Cryptomeria japonica D. Don

seedlings by inducing nitrogen deficiency. Kuo (1973) and Kamienska

et al. (1973) observed precocious flowering in N deficient Cupressus

arizonica Greene seedlings. Sweet and Will (1965) found that precocious










male flowering in radiata pine was associated with low nutrient status.

Giertych (1975) examined the mineral distribution in crowns of Scots

pine and concluded that female flowers were initiated under conditions

of mineral deficiency. Thus, it seems uncertain that mineral nutrition

is truly a limiting factor.

Thinning has been an established silvicultural procedure to increase

growth, and also has been one of the principal methods to increase cone

production. The effects of thinning on fruitfulness have been well

documented and were assumed to be associated with increased light,

moisture, and minerals. The initial response to thinning may have been

due to some kind of stress induced by an abrupt change in environment.

Change has not always been necessary, however, as spacing trials in

red pine (P. resinosa Ait.) showed that cone production was inversely

related to competition (Stiell 1971). The increased light intensity

and temperature have been the most likely candidates for thinning effects;

but it has been difficult to separate the two, since increasing insola-

tion nearly always increases temperature. The positive role of light

and temperature has been supported by climatic associations with cone

crops in conifers. Warm, sunny weather during flower induction favored

good flower crops (Eis 1973, 1976, Zasada et al. 1976, La Bastide and

Van Vredenburch 1970). Also, the distribution of cones within the

crowns of slash pines was strongly related to insolation (Smith and

Stanley 1969). Increasing temperature without increasing light was

effective in experiments involving transfer of Picea sitchensis (Bong.)

Carr. to greenhouses (Tompsett and Fletcher 1977) or covering field-

grown P. abies L. Karst. with polyethylene (Chalupka and Giertych 1977).










Giertych (1976) surmised that high air temperature favored both male and

female flowering whereas high light intensity favored only female flower-

ing.

In addition to the experimental association between vigor-increasing

treatments and flowering, increased flowering has been associated with

various other manifestations of vigor in conifers, such as tree size

(Andersson and Hattemer 1975, Schmidtling 1969), crown size (Grano 1957,

Cappelli 1958), shoot size (Varnell 1970, K. J. Lee 1978), and branch

order (Thorbjornsen 1960, Rim and Shidei 1974). Treatments which had

an obvious deleterious effect on growth and vigor also were associated

with increased flowering. For example, girdling, strangulation, and

binding were used to effect flowering. These treatments were undoubted-

ly stressful, as girdled shoots or trees often died. The immediate

effects were not much different from increased insolation, however, as

carbohydrate accumulated above the girdle (Ebell 1971, Hashizume 1970).

Root pruning or root restrictions and moisture stress have also

increased flowering, but linking these treatments to carbohydrate accumu-

lation was difficult. Root pruning (subsoiling) done in June reduced

the current year's diameter growth, but increased both male and female

flowering in Virginia pines (P. virginiana Mill.) (Greenwood and

Schmidtling 1980). Similarly, transplanting red pines into pots and

continued confinement greatly increased male and female flowering

(Quirk 1973). Confinement in pots has a well-known negative effect

on growth, even if water and nutrients are optimum.







10

Drought, although obviously deleterious to growth, has been shown

to promote fruitfulness, especially if it occurs approximately at the

time of floral initiation. Matthews (1963) listed a number of refer-

ences to climatic studies which have shown this to be true in many

woody plant species, and experimental evidence in loblolly pines was

provided by Dewers and Moehring (1970).

Shoulders (1973) found that abundant rainfall early in the year

followed by a drought increased flowering in slash pines. He proposed

that the early rains favored luxuriant vegetative growth, thereby

increasing photosynthetic capacity. Mild moisture stress in summer

curtailed further vegetative growth, allowing the accumulation of

carbohydrate necessary for floral initiation. This is an attractive

hypothesis, as it can be used to explain how treatments which increase

vigor and those which decrease vigor can both have promotive effects

on flowering.

Greenwood (1978) believed that the presence of a "quiescent" bud

is necessary for an extended period of time during the growing season

to form strobilus initials, and that one of the reasons seedlings do

not flower is that growth is continuous and a quiescent bud does not

exist. He induced bud quiescence by shortening photoperiod and lowering

temperature in early spring in very young loblolly pines. A large

number of strobili were subsequently produced, when none would other-

wise have been expected. Rudolph (1979) noted female strobili but

little additional shoot elongation on 12-month-old jack pine (P.

banksiana Lamb.) which had been grown under optimum conditions for









10 weeks in the greenhouse, and subsequently transplanted to nursery

beds in July. In this case, "quiescence" was induced by transplant

shock.

In the studies relating mineral deficiencies to increased flowering

(Lyr and Hoffman 1964, Kuo 1973, Kamienska et al. 1973, Sweet and Will

1965, Giertych 1975), nutrient deficiencies observed may not have been

the cause. The treatments probably caused an early cessation of growth,

allowing a "resting" bud during the growing season on which initials were

able to form. Thus, many of the conflicting results relating both growth-

promoting and growth-retarding conditions to increased flowering can be

resolved.

Materials and Methods

The study area was a seed orchard, maintained by Region 8 of the

U.S. Forest Service, located in south Mississippi about 25 miles (40 km)

southeast of Hattiesburg. The orchard consisted of ramets from 50

superior loblolly pine selections located on the National Forests in

south Mississippi. There were about 4,000 ramets of these clones

planted at 15 x 30 foot (4.6 x 9.1 m) spacing.

The ortets ranged from 31 to 67 years of age as determined by

increment cores. More than half were between 43 and 54 years of age.

All were reproductively mature, as one criterion for selection was

"some evidence of cone production," when selected or after release

and fertilization. The orchard site was cleared of second growth long-

leaf pine (P. palustris Mill.) in 1961. The area was hilly, as the







12

elevation varied a maximum of 65 feet (19.8 meters). Loamy sands of

five different series made up the soils in this planting, ranging from

an luka loamy sand at lower elevations near a spring-fed stream to a

McLaurin sandy loam on the somewhat drought ridges. A preliminary soil

analysis indicated that the soils were all rather low in NPK. The soils

at lower elevations were generally lower in available P, higher in

total N and organic matter, more acid and generally wetter than those

at higher elevations (Table 1-1).

The orchard was established from 1963 to 1972 using potted grafts

on nursery-run rootstock. Only a few of the clones were represented

among the ramets established the first 3 years, but in 1966 and 1967 more

than 1,000 ramets, well distributed over the 50 clones, were planted each

year. Grafts were planted in 1968 through 1972 to fill in vacant spots

and were also well distributed over the 50 clones, but with very few

ramets per clone.

Male and female flowering, height, and D.B.H. of all ramets were

measured at irregular intervals starting in 1969. Table 1-2 summarizes

the measurements that were taken. Elevation above the stream was also

estimated for all ramets.

The clonal composition varied greatly depending on the year of

grafting. The total set of data was highly unbalanced, so each age

group was analyzed separately. The data thus broken down by year were

simplified into a group of nested designs:

Source of variation Expected mean squares

Clone 02 + Ko2

Ramet/clone 2
w










Table 1-1. Chemical analysis of soil samples taken from two portions
of the Erambert orchard in 1972.


Constituent


Organic matter (%)1

Total nitrogen (%)2

pH1

Extractable phosphorous (ppm)

(Bray II)3

Exchangeable potassium (ppm)1


Location

Lower elevation Ridge

1.116 0.819

0.0284 0.0185

5.3 5.5

3.8 4.1


lJackson (1958)

2Bradstreet (1965)

3Bray and Kurtz (1945)


Table 1-2. Dates on which various traits were measured on all orchard
ramets (indicated by "X").


Parameter
1969


Female strobili

Male strobili clusters


X


Cones


1970

X

X

X


Stem height

Stem D.B.H.


Year measured

1971 1972

X X

X X

X X

X


1973

X

X

X

X

X


1976

X

X

X

X

X










"K" is the harmonic mean number of ramets in clones (Becker 1967).

The genetic model is also very simple. The clonal component of variance,

o2, represents the genetic effect, and heritability is calculated:

02
h2 c
2 + j

The model for computing genetic and environmental correlations

between measured traits is similarly constructed. Since the ramets

are vegetatively propagated, the clonal variance component contains

all genetic variation, nonadditive as well as additive. The herita-

bilities derived are therefore broad-sense.

The number of ramets per clone in each age group varied widely,

so 10 ramets grafted in 1966 were selected from each of 18 clones.

The selected ramets were evenly spread over the orchard to represent

the full range of site variation.

The sample ramets were distributed in the orchard as follows:

1. Lower elevation--three ramets from each clone located on

the luka soils.

2. Middle elevation--four ramets from each clone on the Benndale

soils.

3. Upper elevation--three ramets from each clone on the McLaurin

soils.

In addition to the measurements indicated in Table 1-2, the follow-

ing parameters were measured on the 180 sample ramets:

1. Total seed and sound seed (separated by ethanol flotation) from

a five-cone sample taken in the fall of 1976, 1977, and 1978.










2. Weight per 100 seed in 1978.

3. Yearly diameter growth measured from an increment core (cores

taken at 3 feet above ground) in fall 1976.

4. Counts of male strobili clusters and female strobili in 1977,

1978, and 1979.

5. Height and D.B.H. in 1977 and 1978.

In addition, depth of the A horizon was measured at three equally

spaced points around each ramet, 5 feet from the trunk, with a soil

auger. Soil samples from a depth of 10 centimeters (Al horizon) and 75

centimeters (B horizon) were bulked from the three locations, and sand,

silt, and clay percentages were determined by the Bouyoucos hydrometer

method for each depth.

A competition index (C.I.) was computed for each of the 180 sample

ramets, based on spring, 1976, D.B.H., measurements of the study tree

and the two trees 15 feet (4.6 m) in either direction in the row (between

row spacing was 30 feet (9.1 m), and competition at that distance was

considered negligible). The index was calculated as:

C.I. = ED.B.H.2 (study tree).

This is similar to an index that Daniels and Burkhart (1975) found

effective in describing competition effects on stand development in

loblolly pines.

Environmental effects were analyzed in two ways: (1) by classify-

ing the ramets by soil type (or elevational class) and analyzing

flowering, height, and D.B.H.; and (2) by using regression and correla-

tion to determine relationships of flowering and growth (as dependent

variables) with soils, size of ramet, previous cone crop, etc. (as

independent variables).










All count data were transformed to /count + 0.5. Tests of

statistical significance were at the 0.05 level of probability.

Results and Discussion

Genetic Variation

Yields for all reproductive structures showed a large general

increase with time, as would be expected in a young orchard (Fig. 1-1).

The 180 sample trees seemed to be fairly representative of orchard

production, as they followed the production trend for the whole orchard.

Large year-to-year variation aside from the general increase in produc-

tion was evident, especially in female strobili numbers (Fig. 1-la).

There was an exceptionally good crop of female strobili in 1976, not

only in this orchard but elsewhere in the area. Production the follow-

ing year was lower than 1976, but it probably was near average.

Cone production (Fig. l-lc) followed female flower production,

though survival varied considerably, from 80% in 1970 and 1971 to 33%

in 1973 and 1977. Male strobili production was very low during the

early years, and then expanded tremendously after 1975 (Fig. l-lb).

It increased each year starting in 1976, but decreased in 1979. Female

strobili, on the other hand, showed decreases in 1977 and 1978, and

an increase in 1979. In comparing the yearly patterns of male and

female flowering (Figs. 1-la and l-lb), it was evident that the two

did not seem to be closely related; that is, the increase or decrease

in female flowering did not correspond to an increase or decrease in

male flowering.

Female flowering. Broad-sense heritabilities for female strobili

production varied considerably from year-to-year (Table 1-3). Herita-

bility seemed to increase sharply with age in the younger material,



























Figure 1-1.


Yearly variation in production of reproductive
structures of loblolly pines at the Erambert
Seed Orchard. A. Female. B. Male. C.
Cones. Female strobili in 1975 were estimated
from 1976 cone counts and 1976-1977 stobilus
survival data. Grafts made in 1964 were
included to amplify early flowering trends.
The Y axis was square-root scale.


Line identities:

0 0: Entire orchard
S S: 180 sample ramets
4 4: 1964 grafts












10C -


75 ( A. FEMALE


S
a








-5


/a-.


1969 1970 1971 1972 1973 1974 1975 1976 1977 197 1979
1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979


250 ..

200
B. MALE

150
125
S100
: 75

vr 50
) 40 1
> 30 -
20 /
^ 10
a 5
o o

o, 0 --- 5 ----"
-- I I I I I
1970 1971 1972 1973 1974 1975 1976


30 -


20 1


s5


1977 1978 1979


C. CONES


1969 1970 1971 1972 1973 1974 1975 1976 1977 1978


YERR


\ s s ss











Table 1-3. Broad-sense heritabilities for female flowering by year
for different aged grafts.



Year -------------Year examined--------------------
1969-73
grafted Clones Ramets 1969 1970 1971 1972 1973 a age1 1976
average


No. No. ----------------------h2

63 8 41 0.871 0.687 0.704 0.623 0.420 0.622 0.235

64 13 198 0.600 0.594 0.780 0.673 0.568 0.722 0.345

65 14 56 0.056 0.396 0.527 0.555 0.426 0.490 0.401

66 43 1106 0.326 0.584 0.486 0.595 0.481 0.606 0.441

662 18 180 0.274 0.467 0.270 0.541 0.534 0.593 0.501

67 45 1351 0.268 0.298 0.475 0.370 0.439 0.558

68 34 388 0.477 0.430 0.577 0.304 0.423 0.565

69 34 206 0.204 0.422 0.276 0.356 0.391

70 47 186 0.431 0.299 0.395 0.617


1This is the heritability
the four heritabilities.
2Sample trees--180.
Sample trees--180.


of 1969-73 average flowering, not the average of










but then leveled off and perhaps even decreased with age. Curves

were fitted to the change in variance with age and are shown in Figure

1-2. Variance and heritability were essentially zero before age 3,

as only sporadic flowering occurred before that age. Genetic variance

increased very rapidly from age 3 to age 5, and continued to increase

but at a slower rate to age 13. Apparently the flowering trait was

better expressed among larger trees. The environmental variance increased

sharply at first, likely because of the large variation among ramets in

graft union formation and in subsequent growth. It leveled off some-

what between ages 5 and 9 as more uniform growth occurred. After age

8 or 9, it increased sharply again, probably due to the large variation

in competition among clones. At this age and spacing, 15 x 30 feet

(4.6 m x 9.1 m), within-row competition was beginning to have an effect

but was not uniform. Some of the ramets had essentially no competition

because the ramets on either side were missing or were very small.

Others had trees larger than themselves growing on either side. As a

consequence, variance increased sharply as ramets were affected by

competition in widely varying degrees.

Male flowering. Heritabilities for male strobilus production were

lower than for female strobilus production, and more variable (Table 1-4).

Significant heritable variation occurred only in the older material,

probably due to the low frequency of male flowers before 1976 (Fig. l-lb).

It appeared, however, that eventually the heritability for male flower-

ing would be nearly as high as that for female flowering in older material,

probably above 0.4. The heritabilities for male flowering for grafts



















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23

Table 1-4. Broad-sense heritabilities for male flowering by year for
different aged grafts.


---------------Year examined--------------
Year
grafted Clones Ramets 1970 1971 1972 1973 1970-731 1976
average


No. No. --------------------h2 --

63 8 41 0.069 0.461 0.364 0.243 0.458 0.433

64 13 198 0.245 0.529 0.611 0.016 0.506 0.407

65 14 56 03 0 0 0 0 0

66 43 1106 0.103 0.129 0.165 0.010 0.111 0.272

662 18 180 0.002 0.102 0.168 0 0.055 0.208

67 45 1351 0.243 0.332 0.232 0.037 0.270 0.364

68 36 388 0 0.115 0.065 0.174 0.434


1This is the heritability of 1969-73 average flowering, not the average of
the four heritabilities.

2Sample trees--180.

3Negative heritabilities were assumed to be zero.










made in 1965 inexplicably were always slightly negative or zero (negative

heritabilities were assumed to be zero). Heritabilities for female

flowering for these same trees seemed reasonable (Table 1-3). And many,

but not all, of the same clones were included in the 1964 grafts where

heritability for 1970-1973 average male flowering was computed as 0.506.

The range of clonal means for male flowering was much smaller in the

1965 grafts than in the 1964 grafts, however, and probably accounted for

the low heritabilities. The 1970-1973 average clonal means for male

flowering ranged from 0 to 140 clusters per ramet on the 1964 grafts.

But male flowering ranged from 0 to only 20 clusters per ramet on the

1965 grafts. With respect to clonal variation, the 18 clones in the

sample population seemed to be fairly representative of the 1966 grafts

for both male and female flowering (Table 1-4).

Age and rootstock could bias clonal variation. The age of the ortet

influenced growth (Franklin 1969) and flowering (Schnidtling and Griggs

1976) in slash pines. Ortets in this study did not vary greatly in age

and were all reproductively mature, so age effects were probably minimal.

Correlations based on the 1976 flower crop in the 1966 and 1967 grafts

revealed no important age effect, as the correlation between ortet age

and female flowering was r = -0.053, and between age and male flowering

r = -0.212. Neither of these was significant at the 0.05 level. There

was clearly no age bias in female flowering and very little, if any, in

male flowering.

All ramets in this orchard were grafted on nursery-run seedling

rootstocks, which surely affected variation in growth and flowering.

Schmidtling (1978) found that rootstock variation significantly affected











flowering of loblolly pine grafts. This was true for different species

of rootstock as well as different half-sib loblolly families used as

rootstocks. Specific clonal reactions to grafting, such as incompati-

bility, could have increased clonal variation. But the rootstock

variation undoubtedly contributed substantially to the within-clone

(error or environmental variation), lowering heritabilities. Because

of this, true broad-sense heritabilities were likely higher than those

observed.

Cone and seed yields. Cone and seed production are even more

important aspects of orchard performance than flowering because im-

proved seed are the desired end product of any orchard. In addition

to being affected by the same variables involved in production of the

female strobili from which they are derived, cone and seed production

are further affected by variations in conelet and seed survival. Much

of this added variation is caused by insect predation, but other environ-

mental and genetic factors may contribute to it (McLemore 1977).

Genetic variation in cone production was important, as heritabili-

ties of cone counts were in the same range as heritabilities for female

flowering. (Cone production figures for any given year should be

compared to the previous year's flower production; e.g., the 1970 cone

crop originated from the 1969 flower crop, etc.) The heritability

estimates approached and sometimes exceeded 0.5 but they were highly

variable (Table 1-5). Heritabilities for the 180 sample trees averaged

slightly lower than the 1966 grafts as a whole. In addition to those

listed in Table 1-5, the heritability estimate for cone production was

0.501 in 1977 and 0.648 in 1978 for the 180 sample trees. The genetic









Table 1-5. Broad-sense heritabilities of cone prc-Xcction by year for
different aged grafts.



Year ---------- Year exa-inej-------------
grafted Clones 7.Laets 1969 1970 1971 :172 1973 1976


No. o. --------------------h-------------------

63 8 41 0.593 0.808 0.647 0.375 0.154 0.714

64 13 198 0.550 0.523 0.565 0.763 0.244 0.649

65 14 56 0.571 0.396 0.368 0.329 0.154 0.679

66 43 1106 0.083 0.328 0.507 0.405 0.542 0.535

661 18 180 0.788 0.252 0.429 0.120 0.454 0.454

67 45 1351 0.030 0.238 0.102 0.424 0.534

68 36 388 0.264 0 0.518 0.518 0.300

69 34 206 0.342 0.367 0.368


Sample trees--180.










correlation bet-..-eE flowering and subsequent cone crops was high: r =

0.905 for 1976 fe->le flowers with 1977 cones, an. r = 0.984 for 1977

female flowers .i:- 1978 cones. Those clones with the heaviest flower

crops produced the =.st cones.

Conelet sur-.i--al, i.e., the proportion of female flowers that pro-

duced cones, varied widely among clones, and averaged 32.7% for 1976-

1977 and 63.8% for 1i77-1978 (Tables 1-6 and 1-7). Conelet survival

2 2
was moderately heritable: h= 0.356 for the 1976-1977 crop and h

0.453 for the 1977-1978 crop.

Heavy-flowering clones had a slight tendency to produce a smaller

proportion of surviving cones in the 1976-1977 crop, but not in the

1977-1978 crop. Genetic correlation for the 1976 female flower crop,

with subsequent survival of that crop, was -0.121. For the 1977-1978

crop, which was characterized by a smaller flower crop but much better

survival, genetic correlation was 0.504. Possibly the heavier drain

on nutrients of the larger crops of developing cones adversely affected

survival in a year where the overall crop was heavy. Insect predation

could also have explained the difference. This factor was the major

cause of conelet abortion in loblolly pine (McLemore 1977).

If insect control was poor in 1976-1977, the trees with larger

flower crops could have presented a more favorable situation for insect

population development. This would explain the trend for heavier flower-

ing trees to have a smaller percentage of survivors. On the other hand,

if insect control -as better in 1977-1978, those populations could not

have developed as fully in the heavier flowering trees. Consequently,









Table 1-6. Clonal -3ans for flower, cone and see- yield for the 130
sample riets in 1977.


1976 female& Cones/ Conelet Sound Total
Clone flowers/rsane ramet survival seed/- :n seed/cone

No. No. % No.
A143.0 41.0 38.5 29 36.5

B 102.0 23.8 26.0 26.6 39.8

C 144.0 78.8 62.8 45.$ 63.4

D 238.0 87.3 30.8 59.1 79.3

E 41.0 10.8 46.6 49.8 59.0

F 13.0 7.0 59.3 39.2 52.2

G 191.0 120.7 68.5 37.1 47.8

H 103.0 37.2 52.5 42.3 51.1

I 209.6 60.0 34.7 60.0 77.5

J 16.5 7.5 56.7 37.2 43.9

K 65.0 5.0 10.8 50.7 60.4

L 55.0 2.2 26.8 55.3 58.8

M 177.5 26.9 16.4 40.2 48.9

N 21.0 7.3 28.4 24.1 40.5

0 10.0 4.8 57.0 48.1 53.5

P 118.0 22.1 28.3 17.3 25.7

Q 97.0 9.0 14.2 25.6 30.6

R 239.5 97.0 45.9 56. 81.1

Mean 110.2 36.0 32.7 41.? 52.8
Heritabili- 0.501 0.587 0.199 0.293 0.409
ty

iThis column is based on individual tree data. Trees -ith no flowers were
not included, so it is not the same as the percent cha To'.ld be derived
by dividing average 1978 cones per ramet by average 19-6 flowers per ramet.











able 1-7. Clonal means for flower, cone and seed yield f:r -he 180
sample ramets i. 1978.



1977 female Cones/ Conelet Sound T::a- ,eight of
CLone flower/ramet ra-e: survival seed/cone see: c -- 130 seed


No. o. % No. v. Grams

A 9.2 3.2 30.5 21.7 :?.9 3.2

B 15.1 5.3 29.9 11.5 --.5 3.1

C 51.9 17.0 36.8 7.8 ;.3 3.8

D 117.9 93.3 82.8 17.9 73.3 3.1

E 14.9 8.6 78.0 39.2 65.7 2.6

F 1.5 0.7 33.3 3.2 Pn.5 3.0

G 28.0 26.0 92.3 36.5 63,2 2.8

H 59.8 59.1 86.7 26.6 53.5 3.1

I 19.9 14.6 61.0 23.5 53.0 3.2

J 15.1 14.2 64.8 50.8 6.7 3.3

K 17.6 10.0 44.2 39.6 81.5 3.4

L 11.5 4.2 16.6 22.1 -.1 3.5

M 112.0 88.3 69.0 16.2 56.1 4.0

N 16.2 9.8 56.3 33.4 65.4 2.4

0 7.8 4.9 56.4 40.4 61.3 3.1

P 125.5 93.5 69.6 7.5 15.6 2.6

Q 82.1 49.2 52.3 10.8 -3.5 3.5

R 275.1 202.9 80.6 11.6 -1.3 4.4

Average 54.5 39.2 63.8 23.3 55.4 3.2

Heritabili- 0.629 0.618 0.274 0.307 3.265 0.366











there --as a positive relationship bet.;en flowering and survival.

Genetic : rrelation for conelet surviv-al between the two crops was

positive Dut weak (r = 0.228).

Average yields of total seed per zone varied from 42.3 in 1976

(Table 1-3) to 56.4 in 1978. The yield in 1977 (Table 1-6) was similar

to tha: in 1978 (Table 1-7), 52.8 seed per cone. Clones varied widely

in total seed per cone all 3 years (Tablesl-6, 1-7, and 1-8), with a

three zo fourfold difference between those having the largest and those

having the smallest yields per cone. Heritabilities were moderately

high for total seed per cone (0.241, 0.409, and 0.366 for 1976, 1977,

and 1978, respectively).

Yearly averages of sound seed per cone varied much more than the

total seed per cone. They ranged from 16 per cone in 1976 to nearly

42 per ccne in 1977. Clonal averages of sound seed yields per cone

also varied more widely than total seed, especially in 1976 and 1978.

During those years there was a tenfold or elevenfold difference among

clones. Proportion of total seed which were sound was about 38% in

1976 and 41% in 1978. In 1977, however, nearly 80% of the total seed

was sounc, and there was only a fourfold difference among clones.

The yearly differences in proportion of sound seed was probably

due to variation in effectiveness of insect control. Apparently insect

control was effective in 1977, but not so effective in 1976 and 1978.

Losses :c seed bugs (Leptoglossus corculus [Say]) occurred the year

before c=ne harvest and were manifested as empty and aborted seed. Cone-

let/flcwer losses, on the other hand, occurred mainly in early spring










Table i--. Clonal means for cone and seed yields for the 180
sample ramets in 1976.



Clone Cones per Sound seed Total seed
ramet per cone per cone


------------------------

7.6

2.4

22.1

16.5

1.0

0.1

18.5

8.5

26.1

0.3

0.0

0.8

9.0

2.7

0.9

50.8

6.5

38.1


Mean

Heritability


No.-------- -------

9.5 30.8

18.1 51.9

24.1 61.1

12.9 40.4

15.9 33.1

7.0 25.0

35.4 56.9

18.5 45.3

9.9 46.1

53.5 75.5


5.7

13.0

4.4

4.0

7.2

11.3

21.6


16.0

0.25


11.8

0.45


57.7

53.3

18.6

17.5

23.2

33.7

49.2


42.3

0.24










curing and shortly after flowering (McLemore 1977). The high survival

rae of conelets for the 1977-1978 crop (71.8%), compared with the 1976-

1977 crop (32.7%), also indicated better insect control. McLemore (1977)

showed that most conelet losses in loblolly pines were caused by insects.

Data were not available to attest to the relative degree of insect

losses for the years 1976 through 1978. Some survey data were availalbe

to provide an estimate of the overall seriousness of insect problems in

this orchard. These data were collected in various years to assess the

impact of insect loss and the effectiveness of various treatments.1 In

1975, 85% of female strobili survived on trees sprayed periodically with

the insecticide GuthionR versus 64% on untreated checks. Cones from

trees treated with the systemic insecticide FuradanR averaged 47.6 sound

seed per cone versus 14.3 sound seed per cone in untreated checks in 1976.

For the 1977-1978 flower and cone crop, there was a 21.9% cone loss from

trees treated with FuradanR versus 39.6% from untreated checks. Cones,

caged with a wire mesh to exclude insects, averaged 55 sound seed per

cone in 1978. Uncaged checks averaged only 19 sound seed per cone.

Apparently insects caused heavy losses of female strobili, cones, and

seed in this orchard.

Clonal variation as well as yearly variation in conelet survival

and seed yield could be related to variation in insect predation. Merkel

et al. (1966) found evidence for inherent resistance to coneworm (Dioryc-

tria amatella [Hulst.]) attacks in slash pine.





LData provided by Neil Overgaard, Entomologist, U.S.D.A., Forest
Service, Pineville, Louisiana.










Year x clone interactions. In general, clonal variation in flower-

ir follo~-.ed the general yearly trend; i.e., all clones flower; well

in good years such as 1975, and poorly in bad years such as 197-. The

relative ranking of clones, however, changed considerably from year to

year, as exemplified by 6 of the 18 sample clones shown in Figure 1-3.

Those 6 clones were representative of the range of flowering performances

of the 18 sample clones. The clones varied considerably in female flower-

ing from year to year (Fig. 1-3a), and there seemed to be a lun--term

trend for some clones to move up or down in relative rank. Clone P was

highly variable, and in the early years was the best flowering clone;

but it has been surpassed by several other clones. Clone R, initially

among the poorest, now has become the best.

Strong year x clone interactions were apparent in male flowering,

also (Fig. l-3b). For instance, Clone D was the best pollen producer

during the first 3 years in which measurements were made, but it was

average or only slightly above average the last 3 years. Clone R was

at the bottom during the first 4 years and had no pollen, but it assumed

the number one position the last 3 years. Clone P oscillated year to

year from good to average. An important consequence of such year x

clone interaction in pollen production is that the genetic makeup of

the seed produced by the orchard will vary from year to year, even

for seeds collected separately by female parent. The amount of selfing

could also be expected to vary.

In an analysis of female and male flowering for the years 1976

through 1978, year x clone effects were significant and constituted an

important part of the total variation for both male and female flowering

(Table 1-9). But clonal effects were much greater, and heritabilities





























Figure 1-3.


Year-to-year clonal variation in male and female
flowering of 6 representative clones from the 18
sample clones. Flowering of each clone is ex-
pressed as a percent above or below the mean for
each year. A. Female flowering. B. Male
flowering. Letters refer to clone designation.












A. FEMALE FLOWER::;,


160 -3


S/


80


40


0


-40


-80


P



1f\



A
/ \








PP
A- / A/





/


c





"r
A" /


^. -


1970 1971 1972 -1973 1974 1975 1976


150



100
o

Li
050
C. 50 -


0 0





-50 -
100
--I







-100


1977 1978 1979


3. MALE FLOWERING


---- /



B---g-


- -


N -
- -^ N


YEAR


'- r

IC--NI
N. N -


1970 1971 1972 1973 1974 1975 1976 1977 1978 1979










able 1-9. Analysis of variance and covariance of male and female
flowering for 1976 through 1978 (year effect considered
fixed, all others random).


Source of Degrees of Expected Mean
variation freedom Squares


Clone (C) 17 Ge + YaR2 + YRac
2 2
?amet/Clone (R) 162 e2 + Yo2R

Tear (Y) 2 e2 + Rayc2 + CROy2
e yey
Tear x Clone 34 Ge2 + Rayc2

Error 324 Ce2


Variance-Covariance Components

Variance Variance Correlation
Female Covariance Male Coefficient

Clone 10.88 10.95 17.02 0.805

Ramet 4.82 7.62 18.80 0.801

Year 4.17 -7.72 20.50 -0.835

Year x Clone 3.26 -0.69 3.22 -0.214

Error 5.55 1.45 12.70 0.173

Total 28.68 72.24










for 1976-1978 average male and female flowering were 0.425 and 0.621,

respectively. Although yearly variation and year x clone interactions

were important, the average performance of a clone was highly heritable.

Correlation coefficients computed from the variance-covariance

components showed that male and female flowering were well correlated

by clone (r = 0.805) and by individual ramet (r = 0.801) over the 3

years (Table 1-9). The correlation coefficient for year (r = -0.835)

was strongly negative, however. This indicates that yearly variation

in female flowering has had an opposite basis than for male flowering,

which was evident in comparing Figures 1-la and 1-lb.

In spite of these interactions, female and male flowering for the

whole orchard were correlated positively on a clonal basis, though the

correlations were generally not as strong as in the sample trees.

Those clones with the most female flowers generally were good pollen

producers also. The genetic correlation between male and female flower-

ing in 1976 was almost identical for the 1966 and 1967 grafts (r = 0.589

and r = 0.582, respectively). These were the most reliable figures, as

grafts made in those 2 years had 39 and 45 clones represented, respec-

tively. The 1976 flowering data for the 1966 grafts are shown in Figure

1-4.

One interesting aspect of Figure 1-4 was the number of clones in

the upper left quadrant. These were below average for female strobili

but above average for male strobili. If only female flower or cone

production is used as a basis for preliminary rogueing of an orchard,

some valuable pollen-producing clones might be eliminated. One clone




























I
I


*





t
*


*


tt
*1

* **1
I


*


f.


I I1 4 1 I I -


10 25 50 75 100 150 200

FEHRLE STRlOILI NUMBER / RRHET


Figure 1-4.


Scatter diagram of clonal means for female versus
male flowering. Data were from 10-year-old grafts
in 1976. Dotted lines indicate means for female
flowering (vertical) and male flowering (horizontal).
Both axes are square-root scale.


*



*


* "


0 1










in particular averaged only 1.0 female strobili per ramet, but had

over 50 male strobili clusters per ramet, which was -ore than twice

the average (Fig. 1-4). It would be more logical to limit rogueing

to the clones in the lower left quadrant.

Contribution of each clone to the seed produced. Many tree

improvement personnel are concerned that only a few of their clones

produce the major part of their seed. One tree improvement coopera-

tive estimates that 20% of the clones in their orchards produces 80%

of the seed. This is the so-called "20/80 rule" (N.C. State University

1976). A strong clonal effect was evident in these data, although not

as strong as "20/80."

In this study, sound seed per cone and total cone counts per ramet

indicate that the top 4 of 18 clones (22%) produced 76%, 65%, and 62%

of the total seed produced in 1976, 1977, and 1978, respectively. How-

ever, the top four clones were not the same each year. Figure 1-5 shows

the strong year x clone interaction for seed produced for the top 7 of

the 18 clones. Only one clone ("R" in Fig. 1-5) was included in the

top four all 3 years. On the basis of total seed produced for all 3

years together, the top four clones produced 58.3% of the total seed.

The genetic correlations between number of female flowers and the

number of sound seed produced from that particular flower crop were

very high (r = 0.857 for the 1977 crop, and r = 0.884 for the 1978 crop).

Clones which produced female flowers were the ones which produced the

seeds, despite all the hazards which occurred between formation of the

female strobilus and harvest of full seed.





























1zIp,


I- I


YERR


Figure 1-5.


Yearly seed production of the seven best seed
producers of the 18 sample clones, expressed
as a percent of the total production of all
18 clones each year.


ii
-----B










The theoretical genetic contribution of each of the 18 clones

was computed by using the proportion of sound seed and the proportion

of pollen catkins contributed by each clone at time of pollination.

This was done for the 1977 and 1978 seed crops (1975 pollen data were

not available for the 1976 crop) and results are shown in Table 1-10.

There was a distinct year x clone interaction, as there was with male

and female flowering and seed produced. The top four clones contributed

49% of the genes for the 1977 and 1978 crops, respectively. These

values are somewhat lower than those obtained from seed alone (65%

and 62%, respectively). The present approach assumed that the male

contribution of a given clone was proportional to the number of cat-

kins it produced, which was surely not entirely true.

Clearly, the genetic quality of seed from an orchard can vary

considerably from year to year. This will be true even if seed are

collected from the same mother tree, since pollen composition will

vary from year to year. This undoubtedly accounts for the seed crop

year x genotype interaction observed by C. H. Lee (1978).

Environmental Variation

Soils. Although genetic variation accounted for a large propor-

tion of the variation of many of the characters measured, environmental

variation was also evident in this orchard. It was noted in 1969 that

the trees in the lower elevations were growing better but flowering less

abundantly than the trees located at higher elevations. Those differ-

ences seem to have held up over the years, especially for female

flowering. This seemingly inverse relationship between growth and

flowering suggested the present study.











Table 1-10.


Theoretical genetic contribution of each of the 18
sample clones to the total output in 1977 and 1978.
Based on sound seed and pollen produced in the year
of pollination (selfs excluded). Ranked by 1977
proportion.


Clone Year Rank in 1978
1977 1978


% of total ---------


16.6

13.3

10.4

9.1

8.6

7.7

7.5

6.4

3.9

3.6

3.3

2.9

1.7

1.5

1.1

1.0

0.9


No.


15.9

11.2

4.7

2.8

5.7

4.2

5.6

9.5

9.8

4.3

9.8

6.4

2.0

2.4

3.1

0.0

1.6


0 0.5










According to a U.S. Forest Service soils survey, completed before

the orchard was established, the orchard was planted on five soil series:

luka, Benndale, McLaurin, Van Cluse, and Lucy loamy sands to sandy loams.

The first three types predominated. luka soils are Entisols, and McLaurin

and Benndale are Ultisols of similar taxonomy (Table 1-11). The soils

did not vary greatly in their physical characteristics. luka, an alluvial

soil located in the lower elevations near the stream, had the highest

proportion of sand (85% and 90% at 10 cm and 75 cm depths, respectively)

(Table 1-11). At the other extreme, McLaurin, which was located on the

ridges, had the least sand at both depths (78% and 84% sand in the upper

and lower samples, respectively). Benndale, which was intermediate in

elevation, was intermediate in texture. Clay content of the surface

horizons of these samples varied from 5% to 7%. Differences in textures

were mainly a function of varying proportions of sand and silt.

The relationship of site variables, such as soil texture and eleva-

tion, to flowering were analyzed in two ways: (1) the soil series were

used as a discrete classification variable; each sample tree was classi-

fied according to a soils map, and (2) regressions were used to relate

soil and site variables to flowering, without regard to soil series.

The latter approach was probably the most valid, as soil variations

were continuous and not discrete; and the soils around individual trees

have been rather arbitrarily classified. However, the data can be

presented in a much simpler way with the former approach, so both methods

will be utilized.











Table 1-11. Description of the soils where the IS0 sample trees were
located.

Taxonomic description



Series Family Subgroup Order


luka Coarse-loamy, siliceous, thermic Aquic Udifluvents Entisols

Benndale Coarse-loamy, siliceous, thermic Typic Paleudults Ultisols

McLaurin Coarse-loamy, siliceous, thermic Typic Paleudults Ultisols




Measurements


Soil texture
Series Eleva- Graph Depth 10 cm depth 75 cm depth
tion symbol A horiz. sand silt clay sand silt clay

cm, ---------------------------------

luka Lower 1 31 85 10 5 90 5 5

Benndale Middle 2 35 80 13 7 87 6 7

McLaurin Upper 3 32 78 15 7 84 9 7










Female flowering. Measurements of flowering and growth generally

confirmed earlier observations that flowering was best on soils where

growth was poorest. In general, growth was best on the l-ka soils at

lower elevations (Fig. 1-6). By fall of 1977 the sample ramets on luka

soils averaged 11.1 m in height while those on Benndale and McLaurin

soils averaged only about 10.3 m (Fig. l-6a). Radial growth was clearly

superior for ramets on the luka soil until 1973, when it -as equaled or

surpassed by those on the Benndale soil (Fig. l-6b). As :he sample trees

grew larger, they seemed to be less influenced by soils.

By contrast, flowering was poorer on the soils on which growth was

favored (Fig. 1-7). Flowering was always poorer on the luka soil for

all years measured except the last, though the differences were statisti-

cally significant only in 1972 and 1973.

Although there were differences in flowering and growth of trees

on the different soils, soil texture measurements were infrequently

correlated with either flowering or growth. Female flowering was posi-

tively correlated with elevation in the early years. It was strongest

in 1973 (r = 0.296) and weakest thereafter. This was opposite the early

relationship between growth and elevation, but the trend toward decreasing

the importance of elevation with time was similar.

The variable most strongly and consistently correlated with female

flowering was D.B.H. Correlation increased with age; in 1973 the

correlation between D.B.H. and female flowering was r = 0.295, and in 1976

it was r = 0.524. This seemed to contradict the negative relationship

between growth and flowering by soil series. But the magnitude of these

correlation coefficients allowed for considerable variation due to factors

other than D.B.H. Correlations between D.B.H. and flowering were even































Figure 1-6.


Growth of the 180 sample ramets by soil series.
A. Height. B. Radial growth, measured from
increment cores.


Line identies:


1 1:
2 2:
3 3:


luka soils (lower elevation)
Benndale soils (middle elevation)
McLaurin soils (higher elevation)






47









R. HEIGHT
11 "

10
9


I 7 -
7

6-

I 5
4

3



1969 1970 1971 1972 1973 1974 1975 1976 1977




B. RRDIRL ERDWTH
11

?^ -2--;--1
10



:/
I 9

8 /




S6
/ /

5

1969 1970 1971 1972 1973 197- 1975 1976


YEAR







48


100


75


3
50


1964
30 Grafts 2

20


10


5





0

1969 1970 1971 1972 1973


Figure 1-7.


//

.//

/ /


s8b Sample
SRamets


1974 1975 1976 1977 1978 1979

YERR


Female flowering of the 180 sample ramets and the
1964 grafts by soil series. Vertical axis is
square-root scale. Asterisk indicates differences
were statistically significant.


Line identities:


1 -1:
2--2:
3 -3:
.......:


luka soils (lower elevation)
Benndale soils (middle elevation)
McLaurin soils (higher elevation)
Fitted regression line for flowering/age










stronger when variation due to soil series was removed. This was done

by computing correlation coefficients between D.B.R. and flowering

separately within each of the three soil series, and then pooling the

three values. In 1973, the within-soil correlation coefficient between

D.B.H. and flowering was r = 0.385 compared to r = 0.295 overall; in

1976, the pooled correlation coefficient was r = 0.553 compared to

r = 0.524 overall.

Flowering in a given year was always correlated positively with the

size of the cone crop in the previous year. This was true even for the

1978 female crop, which was preceded by a cone crop varying from 0 to

390 cones per ramet. Correlations ranged from r = 0.286 for previous

cone crop with female flowering in 1971 to r = 0.644 for previous cone

crop with 1978 female flowering.

The positive correlation probably originated solely as a result of

the positive correlation between successive flower crops, which was both

genetic and environmental, and the close correlation between a flower

crop and its subsequent cone crop. Positive correlation between cone

crops and flowering in the subsequent year does not prove, by itself,

that the drain on nutrients of developing cones would not affect flower-

ing. But it suggests that the size of the cone crop, in an operational

seed orchard, probably is not important in determining the next year's

flower crop or inducing periodicity of cone crops.

Effects of competition on growth and female flowering were weak but

significant. The correlation between competition index and 1976 female

flowering was r = -0.183, and that between competition index and 1977

D.B.H. was r = -0.255.










In the stepwise multiple regressions, D.B.H., elevation, and height

were significantly related to female flowering in 1973. Radial growth,

summerwood percent, and percent sand in the A and B horizons were not

significant. The equation

/1973 female flowering + 0.5 = 0.6 + 2.1 D.B.H. + 0.05 elevation

-0.28 height

explained 29.2% of the variation in female flowering. The sign of the

coefficient for height suggests that if D.B.H. and elevation are held

constant, flowering was negatively related to height. The simple correla-

tion coefficient between 1973 female flowering and height was positive

but weak (r = 0.151).

Female flowering in 1977 was significantly related only to D.B.H.,

height, and competition index (Table 1-12). The equation

/1977 female strobili + 0.5 = 6.1 + 2.4 D.B.H. -0.5 height -2.4 CI

explained 28% of the variation in female flowering. Elevation and soil

texture did not enter into the equation, which agrees with the previous

conclusions that the ramets seem to be more independent of site variation

as they increase in size, but competition was important.

One important variable, moisture, was not measured in this experi-

ment and could possibly account for some of the variation not explained

in the multiple regressions. Drought, especially at critical times, can

increase flowering in loblolly pines (Dewers and Moehring 1970, Gallegos

1978). Casual observations during soil sampling in mid-summer indicated

that there was much less soil moisture at higher elevations in the

McLaurin soils than at lower elevations in the luka soils. This might

have accounted for much of the difference in flowering performance,

especially in the earlier years.











Table 1-12.


Stepwise regression relating 1977 female flowering as
a dependent variable with various independent variables.


Independent Regression Standard error Partial F test
variables coefficient


Intercept 6.06 2.80 4.68
1977 ,LE 2.37 0.29 65.17
1977 height -0.51 0.10 25.05
Competition index -2.41 1.17 4.22






Independent variables not in the equation



Variable Partial correlation F to enter



Elevation 0.043 0.33
1976 DBH increment -0.134 3.22
Sand % A horizon -0.049 0.43
Sand % B horizon -0.093 1.55



R2 = 0.283
Overall F = 23.13










Male flowering. The pattern for male flowering was unlike that for

female flowering (Fig. 1-8). For most years, male flowering was best on

the luka soils, exactly opp-site the pattern for female flowering. Differ-

ences in flowering by soil type were significant only in 1976 and 1977.

Size of the grafts might have been a more important factor in male

flowering than in female flowering. Male strobilus production in Pinus

is usually confined to vegetatively less vigorous branches in the lower

part of the crown (Eggler 1961, Wareing 1957). It occurs on Southern

pines mainly on branches in the lower crown that produce only one cycle

of growth during the growing season (Eggler 1961, Greenwood 1979). Small

trees, whether seed grown or grafted ramets, have a relatively small

number of these less vigorous branches. Tree size would not be as

important for female flowering, as female strobili are produced on more

vigorous shoots, such as would occur over the entire crown of a smaller

graft or in the upper crown of larger grafts. This might explain the

lack of agreement between male and female flowering by soil type. The

fact that almost no male flowering occurred in the sample trees before

1976 (Fig. 1-8) supported this hypothesis, because none of these trees

would have had suppressed branches when young, regardless of soil type.

The only independent variables consistently correlated with male

flowering were associated with current size. The coefficients ranged

from r = 0.156 between 1973 male flowering and height to r = 0.537

between 1977 male flowering and D.B.H. In all years except 1976, site

elevation was not related to male flowering. In 1976 the correlation

was weakly negative (r = -0.154) which was opposite that for female

flowering.


















/ /


180 Sapl /
Ra rets / 3
/ 2

"'A


// x


1971 1972 1973 1974 1975


1976 1977 1978 1979


YERR


Figure 1-8.


Male flowering of the 180 sample ramets and the
1964 grafts by soil series. Vertical axis is
square-root scale. Asterisk indicates differ-
ences were statistically significant.

Line identities:

1- 1: luka soils (lower elevation)
2- 2: Benndale soils (middle elevation)
3- 3: McLaurin soils (higher elevation)


1964
Grafts


7
/' >
^


0 4-
1970










In the stepwise regressions, only D.B.H. was correlated signifi-

cantly with male flowering in 1973. The regression equation derived for

1977 male flowering was similar to that derived for 1977 female flower-

ing, as the size variables were the first two entered into the equation.

The equation

/1977 male strobili clusters + 0.5 = 1.7 + 4.0 D.B.H. -0.6 height

-5.7 D.B.H. increment

explained 37% of the variation in male flowering (Table 1-13). Competi-

tion index was just below the significance level required to enter the

equation.

Cone and seed yields. It was anticipated that the drier soils might

have a deleterious effect on conelet survival and seed yields (Gallegos

1978). However, that was not true. If any trend was apparent, it was

opposite to that expected; i.e., yields tended to be poorer on the luka

soils where growth was more favorable. Sound seed per cone, for instance,

varied from 10.9 on the luka soils to 20.0 on the McLaurin soils in 1976.

Similar trends were noted for conelet survival. None of the statis-

tical tests indicated significance, however, even though some of the

means differed substantially. As mentioned previously, most of the

variation in these traits was caused by variability in insect predation.

Although there was fairly strong clonal variation in these traits (Tables

1-6, 1-7, and 1-8), the environmental variation seemed largely random,

at least with respect to soil type.

Cone counts were included as an independent variable in all the

analyses, with the expectation that large cone crops might have a

deleterious effect on cone and seed yields. However, this was not true.














Table 1-13.


Stepwise regression relating 1977 male flowering as a
dependent variable with various independent variables.


Independent Regression Standard error Partial F test
variables coefficient


Intercept 1.69 3.978 0.18
1977 DBH 3.99 0.417 91.52
1977 height -0.57 0.145 15.60
1976 DBH increment -5.66 1.667 11.52







Independent variables not in the equation


Variable Partial correlation F to enter


Elevation -0.092 1.51
Sand % A horizon -0.004 0.00
Sand % B horizon 0.134 1.36
Competition index 0.134 3.20



R2 = 0.370
Overall F = 34.4











The size of the cone crop was always uncorrelated or positively corre-

lated to the cone and seed variables. The strongest example was the

positive correlation between 1978 seed weight and 1978 cone crop.

Variation in the 1978 cone crop was substantial, ranging from 0 to 425

cones per ramet. The overall correlation coefficient was r = 0.424. A

large part of this was genetic (r = 0.612), indicating that those clones

with large cone crops tended to have heavier seed.

Effects of rainfall. Summer rainfall varied considerably over the

10 years of the study (Fig. 1-9) and these variations might explain yearly

variations in flowering. Promotive effects of drought during strobilus

initiation were mentioned previously. Dewers and Moehring (1970) pro-

vide the best experimental evidence for the effects of moisture stress

on reproduction. They subjected loblolly pines to four moisture regimes:

(1) drought the entire growing season, (2) irrigated the entire growing

season, (3) drought April through June, irrigated thereafter, and (4)

irrigated April through June and drought thereafter. Treatments 1, 2,

and 3 were approximately equivalent; trees under treatment 4 produced

twice as many cones as the other treatments.

Figure 1-10 compares the timing of reproductive events in loblolly

pines with a graphical representation of Dewers and Moehring's treat-

ment 4. It was difficult to relate yearly increases in flowering to

climatic variables since flowering was expected to increase each year,

at least in the earlier years. However, some support for the hypothesis

that a rainfall pattern approximating Dewers and Moehring's treatment 4

increased female flowering can be found by comparing Figure l-9a with

Figure 1-9c. Since the effects of moisture on female flowering have






100 A. FEN,.LE FLOWERING


\ _,S


-- 5


S'


69 70 71 72 73 74 75 76 77 78 79


B. MALE FLOWERING







L,..5-- --


5


,S
75


\5


69 70 71 72 73 74 75 76 77 78 79



C. RAINFALL


Figure 1-9.


68 69 70 71 72 73 74 75 76 77 78


YEAR

Yearly variation in flowering compared to early spring
and late growing season rainfall. A. Female Flowering.
B. Male Flowering. C. Rainfall


Line identities:
180 sample ramets
1964 grafts
Average early growing season (April, May, June)
rainfall
Average late growing, season (July, August, September)
rainfall


10


250T


100
I


4--4:
m:










been fairly well documented in the literature, it is more important to

consider the effects of rainfall on male flowering, for which there is no

literature.

Some workers (e.g., Giertych 1967) have claimed that treatments such

as fertilization and hormonal applications might have opposite effects on

male flowering from that on female flowering. However, since male and

female strobili initiate and differentiate at different tines, a treatment

applied at one time might affect their development differently. Consequent-

ly, Greenwood and Schmidtling (1980) reported that such treatments as

fertilization, subsoiling, or hormone application might promote both male

and female flowering if the treatments are properly timed.

Considering the fact that male flower initiation occurs in early

summer and female flower initiation occurs in late summer (Fig. 1-10), it

is reasonable to assume that if drought could influence both male and

female flowering, it should occur at different times. The opposite, or

at least unrelated yearly variation in male flowering compared to female

flowering, can be explained by differences in rainfall patterns. Rain-

fall in 1970 was characterized by low early summer rain and higher late

summer rain (Fig. 1-10c). This was followed in 1971 by a good pollen

crop (Fig. 1-10b, 1964 grafts) and a poor female flower crop (Fig. 1-10a).

The rainfall pattern in 1972 was opposite that of 1970, with higher early

summer rain and lower late summer rain. This pattern was followed by

a poor pollen crop (Fig. 1-10b) and a good female flower crop (Fig. 1-10a),

which was exactly opposite the 1971 pattern.














-o-.ir i













Year 2
Seed Fall



+


Avg.


Figure 1-10.


Pricordia i',it 'a i .






Anthesis Conelet Formaticn





Ernbr'.-?
Cone Grc-t": Fertitiization Deveio e Seed Fall
I 1 i 1 I







Irrigation .. ............. .
Drought Stress



Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
MONTH


Approximate timing of reproductive events in loblolly
pines (above) compared to Dewers and Moehring's (1970)
best cone inducing treatment (below). Timing of repro-
ductive events approximated from Greenwood (1979),
Greenwood and Schmidtling (1980), Eggler (1961), Dorman
and Barber (1956), and Sarvas (1962).










The greatest contrast, not only in rainfall pattern but also in

male and fer-le flowering, was between 1976 and 1978. There was a very

large female flower crop and a poor pollen crop in 1976, whereas 1978

was characterized by a very good pollen crop and poor female flower

crop (Figs. 1-10a and b). These two crops were preceded by rainfall

patternsthat were exactly opposite (Fig. 1-10c); i.e., higher early

summer rain followed by lower late summer rain in 1975, and lower early

summer rain followed by higher late summer rain in 1977.

Greenwood (1978) felt that the critical factor determining flowering

was the existence of a quiescent bud for a sufficient length of time

during the growing season to allow differentiation of primordia. Since

male strobili are formed earlier than female, growth in male flowering

buds would need to cease earlier than female flowering buds. This

normally occurs, as male flowers are often found on branches that had

only one cycle of growth the previous growing season (Eggler 1961,

Greenwood 1979). An early growing season drought might discourage

growth on buds normally expected to produce two or perhaps three cycles,

allowing them to differentiate male strobili. This would not necessarily

encourage female strobili if early drought is followed by abundant rain

in late season, as this often causes renewed growth in buds located in

the upper crown (Schmidtling and Scarbrough 1970) and suppresses female

flowering due to late season bud growth. This could explain the opposite

nature of the yearly variation in male flowering as compared with female

flowering in this study.

A drought early in the growing season appears to favor male flower-

ing, while a drought late in the growing season favors female flowering.









Moisture stress might exert its effect simply by limiting vegetative

growth. Because of changes in rainfall patterns, this would cause not

only yearly variation in flowering, but would also affect site variation

caused by water availability.

Conclusions

Genetic Variation

Large genetic variation exists in fruitfulness in loblolly pines,

with heritabilities ranging from 0.4 to 0.6, indicating that about half

the observed variation is inherent. The biological significance of the

substantial clonal variation is not clear. It seems to contradict the

hypothesized advantage of sexual reproduction under natural forest condi-

tions (i.e., high genetic variability through recombination), since only

a few genotypes would produce a major portion of the reproduction.

Year x clone interactions in male and female flowering would return

some of this variability to the system, because individual trees do not

consistently produce a major part of the seed or pollen every year.

The asynchrony in yearly variation between male and female flowering of

clones provides further yearly variation. As a consequence, large genetic

variation occurs among seed crops.

Evidence from Figure 1-2 shows that this large genetic variation

might not be very important under natural forest conditions. Under

increasing competition, environmental effects seem to increase. However,

high genetic variation might be obtained under some natural conditions

where competition is minimal, such as after a fire, storm, or insect

epidemic where only a few trees are left standing.










,eh-ner or not the high genetic variability is an artifact of

orchard management, it is surely an important factor in tree improvement

for two reasons. First, the number of clones included in many orchards

might be -uch too small. In a 20-clone orchard, there is a good chance

that only four or five of them make a significant contribution to orchard

production. This provides a very narrow genetic base, and also increases

the probability of inbreeding. Second, many clones never produce enough

seed or pollen to justify the expense of maintaining them in an orchard.

If pollen production is used as a criterion, the prospect for identifying

the poorest clones at an early stage is not promising. Clones which are

fruitful early continue to be fruitful. But some that show little

reproductive activity in early years become fruitful later on. Strong

year x clone interactions also make it imperative that fruitfulness be

assessed over a period of several years. This information would normally

be available for cones and seed, but not for pollen which is infrequently

measured. If controlled pollinations for progeny tests are carried out

in the orchard, these data could be easily obtained by assessing relative

production when pollen is collected.

Another consequence of year x clone interactions is the unreliability

of open-pollinated tests of orchard clones, if seeds from different crops

are used in different tests. What might appear as family x site or

family x planting year interactions could be partly due to pollen crop

x year interactions, which cause large differences in male parentage

from year zo year. The same kind of variation could be expected in

various kinds of "check" lots collected in different years.











Environmental Variation

The original observation that environmental conditions which

favored growth did not necessarily favor flowering was reinforced upon

examination of the data. Tree size and overall vigor were important in

determining the size of the flower crop, but continuous growth in the

year of initiation was unfavorable for large flower crops. Limited

quantities of moisture, especially at critical times during the growing

season, seemed important, and probably caused cessation of vegetative

growth and allowed reproductive development.

There seemed to be more underlying similarities between male and

female flowering than previously supposed. Genetic and environmental

factors favoring female flowering appeared to influence male flowering

as well. However, pollen production seems to be inadequate during early

stages of an orchard.

The difference in the timing of initiation, however, might make it

difficult to manage a seed orchard for optimum production of both male

and female strobili. Continuous drought stress would affect the over-

all vigor of the tree and reduce flowering. May through June stress

appeared to increase male flowering, while July through August stress

increased female flowering. May through August stress might increase

both but would be optimum for neither. If an orchard is to be managed

(including irrigation) for both male and female flowering, it might be

necessary to subdivide the orchard. The perimeter, or perhaps a

portion windward to the prevailing winds at time of pollination, could

be managed for pollen production and the rest for female flowering.










The results of this research indicate that the ideal orchard should

be situated on a well-drained to drought site, with an irrigation system.

In the establishment phase and for 3 or 4 years thereafter, water, ferti-

lizers, etc., should be provided to maximize growth to produce a tree

large enough to provide good crops of female and male strobili. After

the establishment phase, vigorous growth will no longer be necessary or

desirable. In the long run, larger trees would make harvesting more

difficult. In the short run, vigorous growth would take place at the

expense of flowering.

When orchard ramets are 4 or 5 years old, irrigation should be

provided as needed, except for July and August, in that portion to be

managed for female flower production. After the orchard ramets are 6 to

7 years old, the part of the orchard managed for pollen production should

be irrigated except during May and June. The additional period of

optimum growth allows larger trees, which would be necessary for pollen

production. Application of fertilizers should also be timed appropriately:

June for the pollen production portion and August for the seed production

portion. Other management practices such as mowing, subsoiling, and

thinning may also be necessary, as will good insect control.















SECTION II
INHERITANCE OF PRECOCITY IN LOBLOLLY PINE
AND ITS RELATION TO GROWTH

Precocious flowering as well as abundant fruiting has obvious

advantages in breeding programs and in the production of improved seed

(Green and Porterfield 1962, Matthews 1963). It is possible the pre-

cocious flowering has already been selected for unintentionally, as

tree breeders develop cultivated varieties from wild strains. Controlled

mating and artificial regeneration may tend to multiply genes that favor

seed production at an early age. This seems to have occurred in Scots

pine, as the "Nye Branch" variety (Gerhold 1966) flowers precociously.

It is important to distinguish between fruitfulness and "ripeness

to flower." Fruitfulness, which was treated at length in the first part

of this dissertation, is a quantitative trait, as it consists of counts

of reproductive structures. "Ripeness to flower," and precocity, the

early expression of "ripeness to flower," are qualitative traits; i.e.,

either the tree has flowered or it has not. This concept also supposes

that once flowering occurs, it is not reversible, even though flowering

may not occur in subsequent years for various reasons.

Trees that direct a great deal of photosynthetic energy into repro-

ductive development at an early age probably do so at the expense of

growth (Ronberger 1967). The study of the inheritance of fruitfulness

and precocity is, therefore, important not only because of its obvious

involvement with seed production and breeding strategy, but also because

of its possible involvement with .growth.










The present study was undertaken with two objectives in mind:

(1 to determine the heritability of precocity and fruitfulness in

loblolly pine seedlings, and (2) to explore the genetic relationship

between fruitfulness, precocity, and growth.

Literature Review

Most woody plants are unable to flower until they attain a stage

or condition known as "ripeness to flower" (Klebs 1918). Normally a

mature tree is considered as having attained this stage and, in most

cases, does not revert to the juvenile condition when propagated

vegetatively (Schaffalitzky de Muckadell 1959). Vegetative propagation

is the favored reproductive method for establishing seed orchards,

because propagules from mature trees normally flower much sooner than

seedlings of the same species (Barber and Dorman 1964).

All of the treatments and conditions which promote flowering in

mature trees, such as fertilization, crown release, subsoiling, and

drought stress, are effective in young trees as long as they have

attained this "ripeness to flowering." However, these treatments do

not seem to be effective prior'to this stage of development (Robinson

and Wareing 1969).

The stimulation of fruitfulness in woody plants therefore appears

to be divided into two areas: increasing the number of flowers in

mature trees, and shortening the juvenile phase to bring about "ripeness

to flower." Precocity and fruitfulness may very well be related, though

the former is a qualitative trait and the latter quantitative. No

information seems to be available as to the relationship between these

two traits in pines, but in pear and apple seedlings precocity and

eventual productivity were unrelated (Visser et al. 1976).









Ability to shorten the juvenile phase could have great utility in

tree breeding programs, since controlled crosses could be made early in

the life cycle of a tree. This would allow a rapid turnover of genera-

tions and an increase in genetic gain. For instance, Greene (1969)

reported potentially large volume gains by breeding precocious loblolly

pines.

Processes governing the phase change from purely vegetative growth

to reproductive growth have been the subject of a great deal of experi-

mentation. Aside from being a feature of advancing age, phase change

seems to be correlated with height in Virginia pines (Bramlett 1971) and

loblolly pines (Schmidtling 1969). Robinson and Wareing (1969) concluded

that the primary factor governing phase change was not dependent upon the

plants passing through a certain number of growing seasons or attaining

a certain size. They experimented with cuttings taken from Ribes nigrum

L. seedlings of various ages, none of which had flowered. They found that

the minimum size for flowering was less for cuttings from older seedlings

than from younger seedlings. They then concluded that phase change

occurred after the plant had passed through a certain minimum number of

mitoses following embryo formation. This was correlated with, but not

determined by, attaining a certain size.

Whether phase change is governed by age, size, or mitotic divisions,

there does seem to be large genetic variation in this trait both between

and within species. Mergen and Koerting (1957) found that flowering

normally begins after about the 5th year in slash pine, but Smith and

Konar (1969) found female strobili in cotyledon stage seedlings of that

species.










There are several accounts of 1-year-old pine seedlings producing

reproductive structures. Nursery-grown seedlings of P. tabulaeformis

Carr. and P. mugo Turra produced male strobili at 1 year (Righter 1939,

Mergen and Cutting 1957), and a P. rigida D. Don seedling of the same age

produced female strobili (Namkoong 1960). Johnson and Critchfield (1978)

found functional male and female strobili on P. contorta x banksiana

hybrids at 1 year of age and presented evidence for the inheritance of

precocity.

Precocious flowering was found to be inherited in Scots pine by

Gerhold (1966) and in jack pine by Jeffers and Nienstaedt (1972), but

they did not determine the mode of inheritance or its relationship to

growth. Teich and Holst (1969) found that one form of precocity was

related to a cone cluster trait, and that a simple dominant gene was

involved in its inheritance, with a possible involvement of cytoplasmic

inheritance. Wright et al. (1966) found substantial variation between

provenances in precocity, but low family (within provenance) variation,

and no relationship between precocity and growth.

In Virginia pine, which normally flowers at an early age, Bramlett

(1971) found high narrow-sense heritability of fruitfulness in seedlings,

and that flowering trees averaged taller than nonflowering trees. In

another study, Bramlett and Belanger (1976) found that fruitfulness was

highly heritable, but negatively correlated with height in parent-progeny

correlations. In both cases, however, precocity was not measured

directly. Flower counts in young seedlings, really more a measure of

fruitfulness, were used.










In contrast to Bramlett's work, Varnell et al. (1967) found fruit-

fulness to have low narrow-sense heritability (h2 = 0.13). Again their

study measured fruitfulness and not precocity. Unfortunately, most of

the authors of papers dealing with the heritability of fruitfulness

(Bramlett 1971, Bramlett and Belanger 1976, Varnell et al. 1967) relied

on counts of strobili which, even in young trees, would contain com-

ponents of both ripeness (contrast between zero and one or more flowers)

and fruitfulness (number of flowers in flowering trees). The two traits

are obviously related, in the sense that one must occur before the other

can be expressed. But they may be governed by separate genetic and

environmental factors. At the other extreme, the two traits may be one

and the same, the precocious trees being those with genomes for heavy

fruitfulness.

Different answers to the question of how precocity is inherited may

be obtained if counts of reproductive structures are used as opposed to

proportion of trees flowering. In an analogous situation dealing with

fusiform rust in loblolly pine, somewhat different results were obtained

when proportion infected was used rather than number of galls (Blair 1970).

Visser et al. (1976) were able to deal with this problem by using

age at first flowering as their precocity criterion. Their precocity

trait was not related to the eventual fruitfulness of the seedlings,

suggesting that genetic control was separate for the two traits. This

kind of analysis is not possible in pines, or most other conifers, since

flowering may never occur in many of the trees under plantation conditions

in a relatively long (10 years) experiment.







70

This necessitated treating "ripeness to flower" as a threshold trait,

and using measures of number of trees flowering rather than age at first

flowering. Relationships among precocity, fruitfulness, and growth are

important in tree breeding programs and have not been adequately determined.

Materials and Methods

Data from two experiments are included in this study, a 10-parent

diallel and a half-sib progeny test.

Diallel. The 10 parents of the diallel were randomly selected

loblolly pines located on the Harrison Experimental Forest in south

Mississippi. These parent trees were crossed in all possible combina-

tions, excluding selfs. The resulting seed were sown in the nursery

in the spring of 1966, and the 1-year-old seedlings were bar-planted in

January 1967 on the Harrison Experimental Forest. Spacing was triangu-

lar, with 9 feet (2.74 m) between rows and 10.39 feet (3.17 m) between

trees in the rows. The experimental design was a randomized complete

block of eight replications with eight trees per plot. Scions from the

parent trees were grafted on potted seedling rootstocks in January of

1967, and the surviving grafts were included in the planting. The grafts

did not grow as well as the seedlings initially, averaging only 1.9 meters

tall at age 3 versus 2.2 meters for the seedlings. In the spring of the

2nd year, each graft was mulched with pine straw and fertilized with 7

pounds (3 kg) of 8-8-8 N-P205-K20 fertilizer. As a result, the grafts

averaged 5.5 meters tall at age 5 versus 3.8 meters for the seedlings.

They were 11.3 meters tall at age 10 versus 10.6 meters for the seedlings.









Female flowers were counted on seedlings and grafts each spring

from 1969 through 1975 (ages 2 through 8 years from planting) except

1973, when measurements on the grafts were not made. Heights were

measured at ages 3, 5, and 10 years, diameters at 5 and 10 years, and

crown width at age 5.

Flowering data were analyzed as binomial traits (zero or one, "ripe-

ness to flower") where a tree was considered "ripe" if ic had flowered

in a given year or in any previous year. These traits were analyzed

untransformed, both on an individual tree basis and on a plot mean basis.

Analysis of a similar trait, fusiform rust, was carried out satisfactori-

ly in this manner (Sohn 1977). Average number of flowers, square-root

transformed, was also analyzed.

The flowering data from the grafts were used only for parent-progeny

regressions. The data from the seedlings were analyzed by a general

least squares analysis program for diallels, "DIALL" (Schaffer and Usanis

1969), on an individual tree basis and a plot mean basis.

The assumptions for the analysis of variance and the genetic variance

expectations are the usual ones for nonrelated, random parents from a

diploid population (Cockerham 1963). Effects accounted for with degrees

of freedom (d.f.) adjusted for missing plots are shown in Table 2-1.

Negative components of variance were handled as recommended by

Thompson and Moore (1963); i.e., a mean square smaller than a prede-

cessor mean square, and whose component was included in it, was pooled

with the predecessor and the result equated to both expectations.









Heritability (h2) estimates were calculated by the formula:

h2 4 o2GCA where the phenotypic variance =
Phenotypic variance

2GCA + 2 + 02
GCA SCA wp
When plot means were analyzed, heritability was computed as:

2 2
0GCA where phenotypic variance = GCA +
Phenotypic variance

O SCA + 2p/8.

Table 2-1. Form of analysis of variance and covariance for the diallel
experiment.



Source D.F. Expected mean squares

Blocks 7

General combining
ability (GCA) 9 o2 + C2 CA + C3 2GCA

Specific combining
ability (SCA) 35 2 p + C1 2SCA

Error 1361 a2wp
(276)1 (a2p)


1Error degrees of freedom are adjusted for missing data.

02wp = Variance component due to error. DIALL computed this by sub-
traction, so it was a pooled error term containing both within-
and among-plot variance.

02 = Variance component due to among-plot error in analyses based
on plot means.

O2SCA= Variance component due to specific combining ability.

o2GCA= Variance component due to general combining ability.

The variance component coefficients Cl, C2, C3, determined by DIALL,

were C1 = 30.8, C2 = 32.8, C3 = 249.1 for individual tree analysis,

and CI = 7.2, C2 = 7.4, C3 = 58.2 for plot mean analysis.










The DIALL program computes the standard deviation of the variance

components as
S2 a (MSi)2
S.D. = -
DFi + 2

where the ai are the coefficients of the linear combination of the mean

squares used to estimate the component (Anderson and Bancroft 1952).

Genetic correlations based on GCA components were calculated also.

Half-sib test. This experiment is of interest primarily because

three of the families were selected for precocity. The test consisted

of open-pollinated progeny of 24 trees, 21 of which were selected for

the National Forest System's Southern Region Tree Improvement Program.

Seed from the select trees were collected from the ortets,which were

located in Mississippi, Alabama, Texas, North Carolina, and South

Carolina.

The three trees selected for precocity were from a fertilizer study

located on the Harrison Experimental Forest. Out of 4,000 loblolly pines

in the study, 12 flowered 2 years after outplanting and 63 flowered after

3 years. All were on fertilized plots (Schmidtling 1971) and the enhanced

flowering appeared to be related to attaining a certain height (Schmidtling

1969). The trees used in the present study were subjected to further selec-

tion, as only 3 of the total of 75 precocious trees produced enough seed

in the 9th year to be included in this study. One of these (Pre-l) had

flowered at age 2, the other two (Pre-2 and Pre-3) at age 3. All three

precocious trees were larger than the plot means at 2 years of age as

well as at 9 years of age when seed were collected (Table 2-2). The fact

that they were taller than average at age 9 might have had an important

role in determining their fruitfulness, as there was intense competition

in the original stands at the 10 x 10 foot (3 x 3 m) spacing.













Table 2-2. Height and diameter of the three precocious parent
trees used in the half-sib study compared to the means
of the 100-tree plots where they were located.





Tree Second year Ninth year Ninth year
height height D.B.H.


m m cm

Pre-1 Select tree 0.94 12.2 20.3

Plot mean 0.77 11.7 16.7


Pre-2 Select tree 0.76 -1 19.1

Plot mean 0.64 10.1 14.9


Pre-3 Select tree 0.73 11.7 15.5

Plot mean 0.68 11.1 15.4




Top broken










Seed collected from the 24 families were sown in the nursery in the

spring of 1970, and the 1-year-old seedlings bar-planted in the winter

of 1970-1971 at two locations on the Harrison Experimental Forest. Four

replications of a randomized complete block were planted at each location,

with four trees per plot and 10 x 10 foot (3 x 3 m) spacing. In spring

of 1977, female flowers, conelets (1-year-old strobili), and cones were

counted and height and D.B.H. were measured. At 4 and 5 years, fruitful-

ness was assessed by cone and conelet counts, respectively. This was

conservative, because some trees without cones or conelets might have had

flowers which aborted.

Mean number of trees flowering per plot was analyzed, and the analysis

took the form:

Source of variation D.F.

Location 1

Blocks in location 6

Families 23

Families x location 23

Error 138

The fixed model was assumed, and statistical significance was tested at

the 0.05 level of probability.










Results and Discussion

Diallel. Approximately 5% of the seedlings flowered in 1969, or

after 2 years in the field. Those are the ones that were considered

precocious. Number flowering increased to over 30% in 1970, and 80% of

the trees had shown some signs of reproduction (age 8) by 1975.

Seedlings actually started flowering before the grafts (Fig. 2-1),

as there was almost no flowering among the grafts in 1969. Undoubtedly

because of physiological maturity and special treatments the grafts

received, they subsequently flowered better than the seedlings. They

averaged over 10 female strobili each in 1974, whereas the seedlings

averaged only about 2.0 each. Yearly variation in flowering of the seed-

lings was approximately parallel to that of the grafts.

Seedlings flowering in 1969 were taller than average at age 3 (Fig.

2-2a). The difference, although statistically significant, was very

small (2.3 m versus 2.2 m for the overall average). Precocious individuals

were still slightly taller than average at age 5, but by age 10 they were

slightly shorter. Differences at ages 5 and 10 were not statistically

significant. Precocious trees continued to flower better than the

average (Fig. 2-2b). In 1973, the difference was largest, when the

precocious trees averaged 12 flowers per tree and the others averaged

only 6. Though the absolute difference varied widely, precocious trees

had about twice as many flowers in all years measured. Possibly the

precocious trees lost their initial height advantage because their energy

was diverted into reproduction.














/\
I


*r


2 3 4 5 6 7 8


RGE YERR5


Figure 2-1.


Flowering of the parent grafts and their seedling
progeny in the diallel experiment. Vertical axis
is square-root scale.


Line identities:

0 0: Grafts
* -- *: Seedlings


10 -







78





T,- .>.. 1* '
7-





t/









3 4 5 6 7 8 9 10


. C!-
#


I

I


I
' I


3 4 5 6 7
fi3 YEfl5


8 9 10


Figure 2-2.


Growth and flowering of the precocious trees
(flowering at age two) compared to the non-
precocious trees in the diallel experiment.
A. Height. B. Flowering. Vertical axis of
B is square-root scale.


Line identities:

- : Precocious
: on-precocious










The diallel analysis showed that all flowering characters exhibited

some degree of heritability (Tables 2-3 and 2-4). These heritabilities

are rather limited in application, and probably could not be used to

accurately predict gain in many breeding situations. They were undoubted-

ly biased upwards because genotype x environment interaction was not

estimated. Exact values are not important, but their relative magnitude

is of interest.

General combining ability (GCA) values for flowering were all more

than two standard deviations above zero, except for 8th-year ripeness on

an individual tree basis (Tables 2-3 and 2-4). Specific combining ability

(SCA) values for flowering traits were generally much smaller than GCA

values. They differed from zero by two standard deviations only in

three instances: 8th-year "ripeness," average number of flowers from

individual tree data (Table 2-3), and average number of flowers from plot

mean data (Table 2-4). Heritabilities ranged from 0.134 for 2nd-year

"ripeness" to 0.609 for average number of flowers on individual tree data.

Values for plot mean data were higher, ranging from 0.409 for 8th-year

"ripeness" to 0.630 for average number of flowers. Thus, average number

of flowers, a quantitative trait, was highly heritable both on an individ-

ual tree basis and on a family basis. This agrees with findings from the

previous chapter. Precocity was much less heritable on an individual

basis, but was moderately heritable on a family (plot mean) basis.











Table 2-3.


Diallel statistics based on individual tree data for
flowering and growth traits. Standard deviations
are shown below general combining ability (GCA) and
specific combining ability (SCA) statistics.


Trait GCA SCA Error h2


Second-year "ripeness"1
(precocity)

Third-year "ripeness"1


Eighth-year "ripeness"1


Average number of
flowers2

Third-year height


Fifth-year height


Fifth-year D.B.H.


Fifth-year crown
width

Tenth-year height


Tenth-year D.B.H.


0.00151
0.00072

0.01270
0.00586

0.55636
0.28038

0.53342
0.23767

0.04270
0.02400

0.09017
0.05158

0.00778
0.00475

0.16969
+0.07854

0.93879
+0.47452

0.06061
0.03227


Having flowered by the year indicated
2 Over the eight years measured


0.00003
0.00034

0.00135
0.00190

0.44334
0.17952

0.09305
0.04351

0.02935
0.02442

0.10353
0.05438

0.01602
0.00583

0.05139
0.02625

0.96583
0.30519

0.08875
0.02618


0.0434


0.1929


10.0605


2.8761


2.3067


3.9821


0.2768


1.8794


10.6353


0.7316


0.134


0.238


0.201


0.609


0.072


0.096


0.104


0.323


0.299


0.275











Table 2-4. Diallel statistics based on plot mean data for
flowering and growth characters. Standard deviations
are shown below General combining ability (GCA) and
Specific combining ability (SCA) statistics.



Trait XCA SCA Error h2


Second-year "ripeness"l
(precocity)

Third-year "ripeness"


Eighth-year "ripeness"l


Average number of
flowers2

Third-year height


Fifth-year height


Fifth-year D.B.H.


Fifth-year crown
width

Tenth-year height


Tenth-year D.B.H.


0.03229
0.00113

0.01475
0.00675

0.00701
=0.00350

0.58433
0.26870

0.06173
0.03372

0.11456
0.06658

0.00783
0.00498

0.15816
0.07381

0.83071
0.43881

0.05578
0.03164


0.00020
0.00071

0.00019
0.00213

0.00448
0.00255

0.17418
0.08518

-0.00680
0.03366

0.06539
0.07578

0.0140
0.00698

-0.00639
0.02955

0.83371
0.36203

0.09542
0.03308


0.1947


0.6110


0.0453


1.3554


1.0286


1.8476


0.1299


0.9058


5.0872


0.3324


0.465


0.653


0.409


0.630


0.324


0.279


0.221


0.583


0.361


0.289


SHaving flowered by the year indicated
2 Over the eight years measured









Heritabilities of the growth variables were much lower than those

for flowering (Tables 2-3 and 2-4). Only the GCA for crown width

differed from zero by more than two standard deviations. Heritabilities

for height seemed to increase :.ith time, however. They reached 0.299 by

the 10th year for individual tree height. In contrast to flowering,

SCA values differed from zero by two standard deviations for several

characters: 5th-year D.B.H., crown width, 10th-year height, and 10th-

year D.B.H. on an individual basis, and for 10th-year height and 10th-

year D.B.H. on a family basis. These results agree fairly well with

those of Snyder and Namkoong (1978) in a longleaf pine diallel. Their

heritabilities for growth traits were in the same range as those found

here. They also noted significant SCA effects for many traits.

Genetic correlations among flowering traits were uniformly high

and positive (Table 2-5), ranging from a low of 0.780 between average

number of flowers and 2nd-year "ripeness" to a high of 1.0 between

average number of flowers and 3th-year "ripeness." Individual tree and

family correlations for each pair of traits were very close, as they

should be.

Genetic correlations between all growth variables and flowering

variables were negative except between 8th-year ripeness and 10th-year

D.B.H., which was essentially zero on a family basis (r = 0.065). Corre-

lations were generally not very strong. But uniformly negative signs

indicate that selection based on fruitfulness or precocity alone would

result in some loss in growth. The strongest genetic correlations were

between 2nd-year "ripeness" (precocity) and various growth traits. They

ranged from r = -0.127 between precocity and height at 3 years for in-

dividuals to r = -0.654 between precocity and crown width for plot means.










Table 2-5.


Genetic (GCA) correlations among flowering variables
and flowering and growth variables from the diallel
analysis. Individual tree correlations are shown
with correlations based on plot mean data below
individual tree correlations in parenthesis.


Average
2nd year 3rd year 8th year number
"ripeness" "ripeness" "ripeness" of flowers


Third-year
"ripeness"1

Eighth-year
"ripeness"'

Average number
of flowers2

Third-year height


Fifth-year height


Fifth-year D.B.H.


Fifth-year crown
width

Tenth-year height


Tenth-year D.B.H.


0.9363
(0.931)4

0.912
(0.780)

0.758
(0.826)

-0.127
(-0.292)

-0.364
(-0.467)

-0.641
(-0.640)

-0.611
(-0.654)

-0.333
(-0.391)

-0.536
(-0.544)


0.959
(0.898)

0.889
(0.870)


1.0
(1.0)


-0.116 -0.440
(-0.167) (-0.401)

-0.350 -0.532
(-0.366) (-0.367)

-0.352 -0.409
(-0.372) (-0.217)

-0.483 -0.399
(-0.514) (-0.235)

-0.348 -0.331
(-0.419) (-0.244)


-0.370
(-0.354)


-0.241
(0.065)


1Having flowered by the year indicated
2 Over the eight years measured
3 Correlation based on individual tree data
4 Correlation based on plot mean data


-0.419
(-0.526)

-0.460
(-0.537)

-0.228
(-0.348)

-0.323
(-0.400)

-0.293
(-0.395)

-0.068
(-0.100)









So even though precocious trees were significantly taller at age 3,

this correlation was environmental since the genetic portion of the

overall correlation was negative. Negative correlations between flower-

ing traits and crown width were surprising, because it seems logical to

assume that trees with larger crowns would have more cones. In this

study, however, there was no genetic evidence for such an assumption.

Parent-progeny relations. Regression between mid-parent average

flowering (average of the two parents for each cross) and progeny average

flowering yielded a heritability of 0.518 (Fig. 2-3). This was slightly

less than the heritability found in the diallel analysis, h2 = 0.609

(Table 2-3). However, the most fruitful parents, in a quantitative sense,

were not the ones which were producing the most precocious progeny. This

was evident in Table 2-6. Parent one ranked fourth out of 10 for average

flowering, but produced the most precocious progeny, 14.7%. The correla-

tion between mid-parent average flowering of the grafts and precocity of

the progeny was only r = 0.355. This increased sharply with subsequent

measures of "ripeness" to a peak of r = 0.680 the 5th year (Fig. 2-4).

Correlations between mid-parent fruitfulness of the grafts and

various growth measures of the progeny were all negative except for the

correlation between 10th-year D.B.H. and parent fruitfulness (r = 0.134).

Correlations between parent fruitfulness and 3rd-year height, 5th-year

height, 5th-year diameter, and 10th-year height were all negative though

weak, ranging from r = -0.241 for 3rd-year height to r = -0.020 for 5th-

year diameter. Though probably not very important, correlations of that

magnitude reinforce the findings of the diallel analysis in cautioning

against selection for fruitfulness without considering other aspects.





























* *


* *


S*


i *


* b = h2 = 0.518


1 5 10 12
Average Female Strobili of M.d-parent o.


Figure 2-3.


Parent-progeny regression for average flowering,
for seven years in the diallel experiment. Both
axes are square-root scale.


0.25 _
0.5











Table 2-6.


Average flowering of the grafts compared to precocity
and average flowering of the progeny in the Diallel
planting.


Parents (grafts) Progeny
Family Average Flowering Precocious Average Flowering


No. % No.

7 14.62 12.7 2.54

9 12.04 3.2 2.05

4 4.09 5.2 1.5

1 3.52 14.7 2.35

8 3.40 6.1 1.77

6 1.93 4.4 .95

3 1.73 6.3 .91

5 1.22 1.4 .77

10 0.83 2.0 .80

2 0.65 2.9 .89


1Flowered at age two
Flowered at age two










0.80 r

0.75..

0.70

0.65.

0.60

0.55

0.50

0.45.

0.40 .


2 3 4 5 6 7 3 k:g.


RGE YERR5


Figure 2-4.


Change in correlation with time between average
fruitfulness of mid-parent and "ripeness to
flower" of progeny. Last point marked "avg" is
the correlation between mid-parent fruitfulness
and progeny average fruitfulness.


/


/
/
/
//


0.35







88

Half-sib test. About 12.5% of the trees in the half-sib test flower-

ed the 4th year (Table 2-7). Flowering increased to 15.6% the 5th year

and to 26.3% the 6th year. Results of selection for precocity were evident.

An average of 32.6% of individuals from the three precocious families

flowered by 4 years compared with an average of 9.6% of the other families.

Over 40% of Pre-1 (precocious family number one) progeny flowered by age 4.

Only one family, Bud 12, equalled flowering of the poorest precocious

family, Pre-3. Differences were statistically significant at all years

and indicated that selection for precocity will result in early flowering

progeny.

Growth of precocious selections was good, contrary to what one would

expect from the negative correlations between flowering and growth in the

diallel analysis. Precocious trees were all larger than average when

selected, however (Table 2-2). Their progeny averaged 5.7 meters tall

compared with 5.4 for the others, and 9.3 centimeters in diameter compared

with 8.6 for the others. One precocious family, Pre-2, ranked first in

diameter out of 24 families. This ranking was remarkable since the 21

nonprecocious families were intensively selected, and size was an important

selection criterion. But geographic variation may be an important factor

in this study, as 11 of the select trees were from areas of slower growing

provenance; i.e., the Tal, Ban, Tex, and Sum sources from north and central

Alabama, Texas, and South Carolina piedmont, respectively (Wells 1969, Wells

personal communication). By excluding the latter, overall mean height of

the remaining select trees was 5.88 meters and D.B.H. was 9.4 centimeters,

slightly larger than precocious selections. But dropping these from the

data does not change differences in flowering between precocious and

select trees.










Table 2-7.


Flowering and growth of the 24 families in the half-sib
study.


Tree Flowering By Age Sixth Year Sixth Year
Family 4 years 5 years 6 years Height D.B.H.


Pre 1
Pre 2
Pre 3
Tal 115
Ban 57
Ban 71
Ban 34
Bud 12
Bud 20
Bud 1
Bud 11
Fra 39
Fra 165
Fra 211
Fra 119
Hom 10
Sum 35
Sum 160
Sum 145
Sum 73
Sum 41
Tex 204
Tex 18
Cro 2
Mean


40.6
30.2
27.1
21.9
15.6
12.5
7.3
27.1
12.5
3.1
0.0
15.6
3.1
13.5
6.3
9.4
12.5
9.4
6.3
6.3
0.0
7.3
6.3
6.3
12.5


50.0
44.8
33.3
21.9
18.8
12.5
7.3
33.3
12.5
3.1
0.0
21.9
10.4.
13.5
9.4
12.5
12.5
16.7
6.3
6.3
0.0
7.3
13.5
6.3
15.6


62.5
64.6
54.2
33.3
41.7
21.9
17.7
40.6
25.0
13.5
0.0
30.2
10.4
32.3
15.6
16.7
31.3
32.3
34.4
13.5
12.5
7.3
13.5
6.3
26.3


m

5.21
6.22
5.66
4.57
4.42
5.17
4.84
5.69
5.21
5.93
5.73
6.40
5.66
6.63
5.52
5.86
4.72
5.14
4.73
5.06
5.49
4.78
5.67
6.14
5.44


cm

8.7
10.7
8.5
6.9
7.4
8.3
7.5
9.6
9.3
8.8
9.2
10.4
8.6
10.3
8.4
9.4
8.0
8.2
7.8
8.1
8.6
7.7
8.9
10.0
8.7


------------%------------









Precocious trees performed better than expected, however, considering

negative relationships that were found between growth and flowering in the

diallel. As stated previously, the two-stage selection process probably

favored fruitfulness as well as growth, since only dominant trees would be

expected to flower under the very close crown competition in which they

grew at age 9. In fact, the three precocious trees used were larger than

their neighbors at age 9 (Table 2-2).

Conclusions

Precocious flowering appears to be moderately heritable, and selec-

tion for this trait can reduce the age of first flowering. Fruitfulness

appears to be highly heritable, and the broad-sense heritability estimates

of the previous chapter for fruitfulness appear to be on the low side.

They probably are biased downward by rootstock effects. Estimates of

broad-sense heritability include all genetic variation and should there-

fore be the upper limit for narrow-sense heritability. The narrow-sense

heritability estimate of 0.609 from the diallel analysis for average

flowering on an individual tree basis is higher than many of the

estimates for broad-sense heritability from the previous chapter. A

broad-sense estimate from Table 2-3 would be:

h2 = 4(GCA + SCA)/phenotypic variance = 0.715

which is greater than any of the estimates from the clonal data.

The previous chapter concluded that size and overall vigor were

positively related to flowering, but that prolonged vegetative growth

discouraged reproductive development. Reproductive biologists tend to

think in terms of "a transition" from vegetative growth to reproductive

growth as part of an overall reproductive strategy (Cohen 1976). Obviously

this does not happen in most forest trees, as growth and reproduction occur







91

within the same growing season. There is no complete transition from

vegetative to reproductive growth as occurs in most herbaceous annuals.

Greenwood (1978) feels that the primary reason seedling pines do not

flower is that they grow almost continuously during the growing season.

He feels that a "quiescent" bud must be formed early in the season to

allow strobilus initials to form.

Thus, whether one views the commencement of reproduction as a change-

over from vegetative growth or as a process where a reduction in vegetative

growth allows reproduction, a negative correlation between reproductive

growth and vegetative growth should be expected. Although this study was

limited by the fact that the conclusions are mainly based on an intensive

analysis of only 10 parents, the expected negative relationship between

growth and repoduction does seem to have a genetic basis in loblolly pines,

which would seem to mitigate against selection based on flowering alone.

The greater height of the precocious trees at age 3 was apparently an

environmental relationship. The genetic correlations between precocity

and all growth variables, including height at 3 years, though weak, were

negative.

The fact that precocity and growth are only weakly correlated suggests

that one could select for both of these traits simultaneously in a breeding

program. The use of genetically induced precocity for obtaining large

gains in growth by shortening generation time, however, hardly seems

feasible.















SU2MARY AND CONCLUSIONS

Genetic Variability

Genetic variability in fruitfulness is certainly an important

consideration in planning loblolly pine tree improvement programs. It

is evident from this study that a relatively small proportion of orchard

clones produce most of the progeny. Most of the genetic variation is

additive, indicating that the use of seedling seed orchards would do

little to solve the problem. In terms of genetic variability, the

effective number of clones in a seed orchard may be less than half the

actual number and could be further reduced by differences in reproductive

phenology. In addition, the negative relationship between cone production

in the parent trees and growth of the progeny indicates not only that few

clones will be producing most of the seed, but that these are not the

best clones with regard to progeny growth.

Under these conditions, early progeny testing assumes even more

importance than previously. Including more selections in breeding

programs also appear warranted. The ideal solution to the problem

would be to find a way to increase flowering in the unfruitful clones.

Unfortunately, the more fruitful clones are the ones which respond best

to treatments such as fertilization. Beers' (1974) suggestion for

fertilizing clones individually by "prescription" based on their previous

response in seed production should, perhaps,be modified to include progeny

test information in the form of an index similar to a selection index.










Relative response to fertilizers, in terms of increase in pounds of

seed produced by each clone, would be included as well as relative

growth of their progeny, to optimize economic gain.

Using precocious individuals to shorten generation time and in-

crease genetic gain should be carried out with caution. In some breeding

programs, selection as early as age 7 is being practiced. It would be

tempting, but risky, to choose trees above average in growth from progeny

tests primarily because they flower early. If precocious individuals are

selected which are very much above average in growth, however, the risks

are probably not great, since the heritability of precocity is only

moderate to weak. Also, the genetic correlation with growth is not

strong. Selection based on precocity alone seems to be clearly un-

warranted.

Environmental Variability

There is ample evidence from previous studies showing that abundant

production of seed reduces vegetative growth. The converse also appears

to be true; i.e., reduced vegetative growth enhances the production of

seed. The best conditions for vegetative growth appear to be less than

optimum for reproductive growth. Some sites which have been carefully

chosen for seed orchards may be too good. Previously, it was assumed

that the best sites for vegetative growth would be the best for seed

production, but it is apparent that conditions which favor cessation of

growth early in the season are best for flowering.







94


Silvicultural treatments such as fertilization and irrigation need

to be optimized to favor vegetative growth in the establishment phase,

as size is very important in determining fruitfulness. After the orchard

is in production, these silvicultural treatments need to be changed to

optimize reproductive growth. This may require an adjustment in the

attitude of seed orchard managers.















LITERATURE CITED


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research. McGraw-Hill, New York. 399 p.

Andersson, E., and H. H. Hattemer. 1975. Growth and flowering of pri-
mary and secondary grafts of Scotch pine. Silvae Genet. 24:49-54.

Barber, J. C., and K. W. Dorman. 1964. Clonal or seedling seed orchard?
Sil-ae Genet. 8:11-17.

Barnes, B. V. 1969. Effects of thinning and fertilizing on production
of western white pine seed. U.S.D.A. For. Serv., Intermt. For. and
Range Exp. Stn. Res. Pap. INT-58, 14 p.

Barnes, R. L., and G. W. Bengtson. 1968. Effects of fertilization,
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Becker, W. A. 1967. Manual of procedures in quantitative genetics.
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Beers, W. L., Jr. 1974. Industry's analysis of operational problems
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rust in loblolly pine. Ph.D. Thesis, N.C. State Univ., Raleigh, 87 p.

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Bramlett, D. L. 1971. Correlations between reproductive and vegeta-
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Bramlett, D. L., and R. P. Belanger. 1976. Fertilizer and phenotypic
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