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Copyright 2005, Board of Trustees, University
STAGES IN CONELET
DEVELOPMENT IN SLASH PINE
D. L. Rockwood
Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
John T. Woeste, Dean for Extension
STAGES IN CONELET DEVELOPMENT IN SLASH PINE
D. L. Rockwood
Assistant Professor, School of Forest Resources and
Conservation, University of Florida, Gainesville 32611
Correct timing of application of pollen is crucial to the success
of much breeding work in slash pine (Pinus elliottii Engelm.). One
application, mass-pollination of seed orchards to produce inter-
specific hybrids or yield progeny having only certain male parents
is dependent on properly synchronized pollen dissemination. A
more common procedure, controlled-crossing by applying specific
pollen to one or more isolated female conelets, is a necessary part
of slash pine breeding.
This circular describes the stages of conelet development that
relate to successful pollination. The photographs of these stages in
conjunction with techniques described elsewhere should enable
the seed orchard manager or tree breeder to utilize the limited
time of conelet receptivity effectively. Also, climatic and genetic
factors affecting pollination are discussed.
To illustrate the stages of development, female flowers on one
tree were observed during Winter, 1977. The tree was located near
Gainesville, Florida, in a clone bank maintained by the Coopera-
tive Forest Genetics Research Program (CFGRP I at the University
of Florida. Observations commenced on January 14 and continued
STAGES OF DEVELOPMENT
The development of conelets with respect to the pollination
process has been divided into 4 stages (2,4):1 Stage I the female
flower buds elongate, Stage II the developing conelets emerge
from the bud, Stage III conelet scales are open and conelets
are receptive, and Stage IV conelet scales close and pollination is
impossible. Our photographs illustrate these stages and addition-
ally show the changes of color that conelets undergo during
development. An excellent summary of control pollination tech-
niques given originally by Mergen, et al., (3) is presented by
1Numbers in parentheses refer to Literature Cited
Figure 1. a) Female flower buds on January 14, 1977: Stage I.
Figure 1. b) Female flower buds on January 28, 1977: late Stage I.
Female flower buds, situated below the vegetative bud-tip,
typically are recognizable in December. One, two, or occasionally
more flower buds will occur near a branch tip. Our first photo-
graph shows three flower buds in Stage I easily identifiable with
Figure 1. c) Conelet emergence on February 1, 1977: early Stage II.
Figure 1. d) Conelets on February 11, 1977: late Stage II.
their whitish bud scales (Figure la). The female flowers stayed in
Stage I for another 2 weeks (Figure Ib). For control-pollinations,
bagging of flowers should be completed during this stage. Stage II
commenced with the conelets emerging from the buds (Figure Ic).
Figure 2. a) Female conelets with opening scales on February 14, 1977:
early Stage III.
Figure 2. b) Female cone-
lets on February 16, 1977:
Figure 2. c) Female cone-
lets on February 17, 1977:
late Stage IlI.
Figure 2. d) Closed conelets: Stage IV.
Conelets continued to emerge for about 19 more days (Figure Id).
Note that conelet scales are still closed, and the conelets are
In Stage III, conelet scales open to nearly right angles with the
axis of the conelet. The conelets appear pinkish (Figures 2a, b, c).
At the peak of Stage III, the ovules may be seen at the base of the
conelet scales. Stage III will last a very short time; pollen must be
applied during this stage.
Stage IV is characterized by a swelling of the conelet scales with
subsequent closing of the conelet (Figure 2d). Conelets lose the
pinkish color common to Stage III. Pollination at this time is not
possible as pollen cannot enter the conelet. Pollination bags can be
removed without fear of contamination from other pollen sources.
CLIMATIC INFLUENCES ON CONELET DEVELOPMENT
Temperatures during the winter have a significant influence on
conelet development. Usually pollination occurs in north Florida
in late January or early February, and the time required to go
from Stage I to Stage IV is about 15 days (2). Cold temperatures
will suppress development and defer effective pollination time.
The winter of 1977 was unusually cold in Gainesville, and the
one tree observed was not receptive until mid-February. Nearly
three weeks were needed for the conelets to move from Stage I to
Stage IV. Winter, 1978, was even more severe, and slash pines were
generally not receptive until mid-March.
The seed orchard manager or tree breeder must anticipate the
peak receptivity in order to effectively coordinate his efforts.
Climatic data, specifically, daily maximum temperatures, may
be utilized by the technique presented by Boyer (1) to develop a
target period for peak pollen shed of slash pine and other southern
pines. Once close to the target date for pollen shed, frequent ob-
servations of conelet receptivity of the involved trees should be
made to identify the actual time of receptivity.
TREE-TO-TREE VARIATION IN CONELET DEVELOPMENT
A considerable degree of genetic variation in flowering time in
slash pine has been noted in the CFGRP. We have repeatedly
observed a large number of clones and found that classifications
such as early, average, and late flowering are consistent from year
to year. The difference in time of receptivity of an early clone
compared to a late clone may be as much as three weeks.
Anyone planning a large-scale pollination program involving
several clones should know in advance what the relative flowering
times of the clones are. With this information, more efficient
schedules for bagging and pollination are possible.
1. Boyer, W. D. 1978. Heat accumulation: an easy way to anti-
cipate flowering of southern pines. J. For. 76:20-3.
2. Dorman, K. W. 1976. The genetics and breeding of southern
pines. USDA For. Serv. Agr. Handbook No. 471, 407p.
3. Mergen, F., H. Rossoll, and K. B. Pomeroy. 1955. How to con-
trol pollination of slash and longleaf pine. USDA For. Serv.
Southeast. For. Exp. Sta. Pap. 58, 14p.
4. Snow, A. G., Jr., K. W. Dorman, and C. S. Schopmeyer. 1943.
Developmental stages of female strobili in slash pine. J. For.
This publication was printed at a cost of
$498.90, or 99.9 cents per copy, to identify
factors influencing pollination timing of slash
pine to improve breeding work with the
Single copies are free to residents of Florida and may be ob-
tained from the County Extension Office. Bulk rates are
available upon request. Please submit details of the request to
C. M. Hinton, Publication Distribution Center, IFAS Building
664, University of Florida, Gainesville, Florida 32611.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Cooperative Extension Service, IFAS, University of Florida
and United States Department of Agriculture, Cooperating
K. R. Tefertiller, Director