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 Title Page
 Table of Contents
 Credits
 Introduction
 Cause and development of the...
 Definition of the problem
 Methods of experimentation
 Resistant strains from commercial...
 Resistant strains from crosses
 Discussion
 Summary














Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 226
Title: Development of strains of cigar wrapper tobacco resistant to blackshank (Phytophthora nicotianae Breda de Haan)
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027325/00001
 Material Information
Title: Development of strains of cigar wrapper tobacco resistant to blackshank (Phytophthora nicotianae Breda de Haan)
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 45 p. : ill. ; 23 cm.
Language: English
Creator: Tisdale, W. B ( William Burleigh ), 1890-
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1931
 Subjects
Subject: Tobacco -- Disease and pest resistance -- Genetic aspects   ( lcsh )
Phytophthora nicotianae   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references.
Statement of Responsibility: by W.B. Tisdale.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
 Record Information
Bibliographic ID: UF00027325
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924073
oclc - 18176426
notis - AEN4677

Table of Contents
    Title Page
        Page 1
    Table of Contents
        Page 1
    Credits
        Page 2
    Introduction
        Page 3
    Cause and development of the disease
        Page 4
    Definition of the problem
        Page 5
    Methods of experimentation
        Page 6
        Page 7
        Page 8
    Resistant strains from commercial varieties
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
    Resistant strains from crosses
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
    Discussion
        Page 40
        Page 41
        Page 42
    Summary
        Page 43
        Page 44
        Page 45
Full Text



Bulletin 226 March, 1931


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
Wilmon Newell, Director






DEVELOPMENT OF STRAINS OF

CIGAR WRAPPER TOBACCO

RESISTANT TO BLACKSHANK

(PHYTOPHTHORA NICOTIANAE

BREDA DE HAAN)


By W. B. TISDALE





TABLE OF CONTENTS
Page
Cause and Development of the Disease.......... ... .. ... .. 4
Definition of the Problem ....... ....... ... .... .. .. ..... ...... .. 5
Methods of Experimentation.. ..... ........... .... 6
Resistant Strains from Commercial Varieties. ... .......... ...... .. .... ........ 9
B ig C uba .. ............. .. .. .... ...... .......... .... 10
Little Cuba ........ ... .. ..... ....... .. .. .... ........... ............ 16
Santiago .................. 17
D ubek ....................... ...............18
Resistant Strains from Crosses ................ ................ ... 18
N o 1 .............. .......................... .. ............ 19
R ....... 23
301 ... ......... ....... ............ 27
94 ....................... .. 35
O their C roses ...................... .. .... ........... ... ............ .......................... 40
D discussion ... ........ .......... .... ... .................... 40
Sum m ary ............... ..... ........ ............ .. .. ............ ................. 43




TECHNICAL BULLETIN

Bulletins will be sent free upon application to the
Agricultural Experiment Station
GAINESVILLE, FLORIDA







Bulletin 226 March, 1931


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
Wilmon Newell, Director






DEVELOPMENT OF STRAINS OF

CIGAR WRAPPER TOBACCO

RESISTANT TO BLACKSHANK

(PHYTOPHTHORA NICOTIANAE

BREDA DE HAAN)


By W. B. TISDALE





TABLE OF CONTENTS
Page
Cause and Development of the Disease.......... ... .. ... .. 4
Definition of the Problem ....... ....... ... .... .. .. ..... ...... .. 5
Methods of Experimentation.. ..... ........... .... 6
Resistant Strains from Commercial Varieties. ... .......... ...... .. .... ........ 9
B ig C uba .. ............. .. .. .... ...... .......... .... 10
Little Cuba ........ ... .. ..... ....... .. .. .... ........... ............ 16
Santiago .................. 17
D ubek ....................... ...............18
Resistant Strains from Crosses ................ ................ ... 18
N o 1 .............. .......................... .. ............ 19
R ....... 23
301 ... ......... ....... ............ 27
94 ....................... .. 35
O their C roses ...................... .. .... ........... ... ............ .......................... 40
D discussion ... ........ .......... .... ... .................... 40
Sum m ary ............... ..... ........ ............ .. .. ............ ................. 43




TECHNICAL BULLETIN

Bulletins will be sent free upon application to the
Agricultural Experiment Station
GAINESVILLE, FLORIDA








BOARD OF CONTROL
P. K. YONGE, Chairman, Pensacola BAYMER F. MAGUIRE, Orlando
A. H BLENDING, Leesburg FRANK J. WIDEMAN, West Palm Beach
W. B. DAVIS, Perry J. T. DIAMOND, Secretary, Tallahassee

STATION EXECUTIVE STAFF
JOHN J. TIGERT, M.A., LL.D., President R. M. FULGHUM, B.S.A., Asst. Editor
WILMON NEWELL, D.Sc., Director IDA KEELING CRESAP, Librarian
H. HAROLD HUME, M.S., Asst. Dir., Re- RUBY NEWHALL, Secretary
search K. H. GRAHAM, Business Manager
S. T. FLEMING, A.B., Asst. Dir., Admin. RACHEL McQUARRIE, Accountant
J. FRANCIS COOPER, M.S.A., Editor

MAIN STATION-DEPARTMENTS AND INVESTIGATORS


AGRONOMY
W. E. STOKES, M.S., Agronomist
W. A. LEUKEL, Ph.D., Associate
G. E. RITCHEY, M.S.A., Assistant*
FRED H. HULL, M.S., Assistant
J. D. WARNER, M.S., Assistant
JOHN P. CAMP, M.S.A., Assistant
ANIMAL HUSBANDRY
A. L. SHEALY, D.V.M., Veterinarian in
Charge
E. F. THOMAS, D.V.M., Asst. Veterinarian
R. B. BECKER, Ph.D., Associate in Dairy
Husbandry.
W. M. NEAL, Ph.D., Assistant in Animal
Nutrition
C. R. DAWSON, B.S.A., Assistant Dairy
Investigations
CHEMISTRY
R. W. RUPRECHT, Ph.D., Chemist
R. M. BARNETTE, Ph.D., Associate
C. E. BELL, M.S., Assistant
J. M. COLEMAN, B.S., Assistant
H. W. WINSOR, B.S.A., Assistant
H. W. JONES, B.S., Assistant
COTTON INVESTIGATIONS
E. F. GROSSMAN, M.A., Assistant
PAUL W. CALHOUN, B.S., Assistant


ECONOMICS, AGRICULTURAL
C. V. NOBLE, Ph.D., Agricultural Economist
BRUCE McKINLEY, A.B., B.S.A., Associate
M. A. BROOKER, M.S.A., Assistant
ECONOMICS, HOME
OUIDA DAVIS ABBOTT, Ph.D., Head
L. W. GADDUM, Ph.D., Biochemist
C. F. AHMANN, Ph.D., Physiologist
ENTOMOLOGY
J. R. WATSON, A. M., Entomologist
A. N. TISSOT, M.S., Assistant
H. E. BRATLEY, M.S.A., Assistant
L. W. ZIEGLER, B.S., Assistant
HORTICULTURE
A. F. CAMP, Ph.D., Horticulturist
HAROLD MOWRY, B.S.A., Associate
M. R. ENSIGN, M.S., Assistant
A. L. STAHL, Ph.D., Assistant
G. H. BLACKMON, M.S.A., Pecan Culturist
C. B. VAN CLEEF, M.S.A., Greenhouse
Foreman
PLANT PATHOLOGY
W. B. TISDALE, Ph.D., Plant Pathologist
G. F. WEBER, Ph.D., Associate
A. H. EDDINS, Ph.D., Assistant
K. W. LOUCKS, M.S., Assistant
ERDMAN WEST, B.S., Mycologist


BRANCH STATION AND FIELD WORKERS
L. O. GRATZ, Ph.D., Asso. Plant Pathologist in charge, Tobacco Exp. Sta. (Quincy)
R. B. KINCAID, M.S., Assistant Plant Pathologist (Quincy)
W. A. CARVER, Ph.D., Assistant, Cotton Investigations (Quincy)
RAYMOND M. CROWN, B.S.A., Field Asst., Cotton Investigations (Quincy)
JESSE REEVES, Farm Superintendent, Tobacco Experiment Station (Quincy)
J. H. JEFFERIES, Superintendent, Citrus Experiment Station (Lake Alfred)
GEO. D. RUEHLE, Ph.D., Assistant Plant Pathologist (Lake Alfred)
W. A. KUNTZ, A.M., Assistant Plant Pathologist (Lake Alfred)
B. R. FUDGE, Ph.D., Assistant Chemist (Lake Alfred)
W. L. THOMPSON, B.S., Assistant Entomologist (Lake Alfred)
R. V. ALLISON, Ph.D., Soils Specialist in charge Everglades Experiment Sta. (Belle Glade)
R. W. KIDDER, B.S., Foreman, Everglades Experiment Station (Belle Glade)
R. N. LOBDELL, M.S., Assistant Entomologist (Belle Glade)
F. D. STEVENS, B.S., Sugarcane Agronomist (Belle Glade)
H. H. WEDGEWORTH, M.S., Associate Plant Pathologist (Belle Glade)
B. A. BOURNE, M.S., Associate Plant Physiologist (Belle Glade)
J. R. NELLER, Ph.D., Associate Biochemist (Belle Glade)
A. DAANE, Ph.D., Associate Agronomist (Belle Glade)
FRED YOUNT, Office Assistant (Belle Glade)
M. R. BEDSOLE, M.S.A, Assistant Chemist (Belle Glade)
A. N. BROOKS, Ph.D., Associkte Plant Pathologist (Plant City)
R. E. NOLEN, M.S.A., Field Assistant in Plant Pathology (Plant City)
A. S. RHOADS, Ph.D., Associate Plant Pathologist (Cocoa)
C. M. TUCKER, Ph.D., Associate Plant Pathologist (Hastings)
H. S. WOLFE, Ph.D., Associate Horticulturist (Homestead)
L. R. TOY, B.S.A., Assistant Horticulturist (Homestead)
STACY O. HAWKINS, M.A., Field Assistant in Plant Pathology (Homestead)
D. G. A. KELBERT, Field Assistant in Plant Pathology (Bradenton)
FRED W. WALKER, Assistant Entomologist (Monticello)
D. A. SANDERS, D.V.M., Associate Veterinarian (West Palm Beach)
M. N. WALKER, Ph.D., Associate Plant Pathologist (Leesburg)
W. B. SHIPPY, Ph.D., Assistant Plant Pathologist (Leesburg)
C. C. GOFF, M.S., Assistant Entomologist (Leesburg)
J. W. WILSON, Ph.D., Assistant Entomologist (Pierson)
*In cooperation with U. S. Department of Agriculture.








DEVELOPMENT OF STRAINS OF CIGAR WRAPPER
TOBACCO RESISTANT TO BLACKSHANK (PHY-
TOPHTHORA NICOTIANAE BREDA DE HAAN)

By W. B. TISDALE

Blackshank is the most destructive disease of shade-grown
tobacco in the Florida-Georgia district. So far it has not proved
to be of equal economic importance with flue-cured tobacco in
that district because of the long-time rotation system used and
of the availability of large acreages of land on which this crop
has never been grown. However, flue-cured tobacco is quite
susceptible to the disease and when it is planted on infested land
or on land which becomes infested during the growing season,
the crop is often a total failure. The disease was reported in
1930' to be quite serious locally with flue-cured tobacco in North
Carolina. Prior to that time the disease had been reported only
from Alabama, Florida, Georgia, and Virginia in the United
States." Outside of the United States blackshank occurs in
most of the older tobacco-growing countries located in the tropics
or sub-tropics. It appears therefore that the disease is becom-
ing a serious problem in the culture of all types of tobacco in
countries and localities having a long growing season of rela-
tively high temperature.
A study of the disease was begun in Gadsden County in 1922
and the general facts regarding the cause and nature of the
disease and the preliminary results with control measures were
discussed in previous reports." Since that date the work has
been continued with encouraging advances in control measures,
especially through disease resistance. The purpose of this paper
is to describe the methods used in the development of resistant
strains of cigar wrapper tobacco and to record the salient results
of the experimental work.
Before discussing the details of this experimental work the
cardinal points in connection with the nature and destructive-
ness of the disease will be given.
1In letters from F. A. Wolf and R. F. Poole.
'Tisdale, W. B., and J. G. Kelley. A Phytophthora disease of tobacco.
Fla. Agr. Exp. Sta. Bul. (Tech.) 179:159-218. 1926. illus.
"Tisdale, W. B. Tobacco diseases in Gadsden County in 1922 with sug-
gestions for their prevention and control. Fla. Agr. Exp. Sta. Bul. 166:
77-118. 1922. illus.
'Wingard, S. A., and James Godkin. Tobacco diseases in Virginia and
their control. Va. Agr. Exp. Sta. Bul. 90:3-31. 1924. illus.






Florida Agricultural Experiment Station


CAUSE AND DEVELOPMENT OF THE DISEASE
Blackshank of tobacco is caused by the soil-inhabiting fungus
Phytophthora nicotianae Breda de Haan. This fungus has been
found to attack roots, basal portions of the stalks and, under
certain conditions, the leaves of tobacco plants at any stage of
growth. In Florida blackshank is chiefly in evidence in the field
after transplanting, although it may appear occasionally in the
plant bed, especially if the bed is flooded by drainage water from
infested fields after the plants are well advanced. Its failure
to appear regularly in the plant beds in Florida is because the
temperature is usually too low for infection to occur while the
seedlings are in the beds. In certain countries tobacco seed is
sown at a time when the soil temperature is favorable for in-
fection by Phytophthora nicotianae. Under such conditions the
disease may be a limiting factor in the production of tobacco
seedlings. It has been reported to be especially destructive in
plant beds in Porto Rico.'
Plants usually succumb to attacks of the disease within a few
days, if they are transplanted to infested soils late in the season
after the soil temperature is relatively high. On the other hand,
if the plants are transplanted in the tobacco district of Florida
before April 1, they grow vigorously until they are from 10 to
18 inches high before showing signs of the disease. This is be-
cause the parasite is unable to invade the host aggressively
until the soil temperature reaches 20C. and above. The optimal
temperature for development of the disease has not been de-
termined but information obtained indicates that it is several
degrees above 200C.
Under conditions of high humidity and favorable temperature
the fungus attacks the stems and leaves of tobacco seedlings and
produces a characteristic dark, wet rot similar to late blight of
potato. With older plants the disease is primarily a dry rot
of the roots and basal portion of the stem, although the lower
leaves may be attacked during prolonged rainy periods. The
fungus usually attacks first the tap-root or main laterals and
rapidly invades and kills all parts of the root system and the
lower portion of the stalk. This leads to sudden wilting and the
progressive browning and death of the aerial parts of susceptible
plants within a few days. Less susceptible plants may wilt dur-
"Nolla, J. A. B. The black shank of tobacco in Porto Rico. (Abstract)
Phytopath. 19:93-94. 1929.







Bull. 226, Development of Resistant Cigar Tobaccos 5

ing the day and recover at night for some time and finally persist
in a stunted condition and blossom prematurely.
When the soil is once infested, the fungus seems capable of
persisting almost indefinitely after the land has been abandoned
for tobacco culture. The results of several trials have shown
that the fungus is present in sufficient amount after six or eight
years to cause heavy loss when the land is planted again to a
susceptible variety. On the other hand, trials in certain fields
have indicated that the infestation was materially reduced after
a period of from one to three years. Furthermore, differences
in severity of the disease have been observed on certain types
of soil from year to year, but all the factors which may cause
this erratic behavior have not been ascertained. Although the
possible variation in the pathogenicity of the parasite has not
been overlooked, cultures of the organism isolated from diseased
tobacco plants growing in different types of soil and in different
localities have proved equally pathogenic in inoculation experi-
ments.
In any event, the period of survival in the soil is too long for
any rotation system to be practical with tobacco grown under
slat shade. Furthermore, the various methods of soil treat-
ment have proved equally impractical for eradicating the para-
site. On account of the numerous agencies which may dissem-
inate the parasite from field to field and the rapid progress of
the disease in a field once the soil has become infested, the culture
of susceptible varieties of shade tobacco is fraught with great
risk on farms or in localities which have infested areas. It is
therefore natural that with the increasing importance of the
disease a keen demand has arisen for resistant strains conform-
ing in type and quality to the demands of the trade.

DEFINITION OF THE PROBLEM

As already noted' 7, resistant strains of the local variety, Big
Cuba, have been secured by selecting and propagating self-pol-
linated individuals that survived on uniformly infested soils. By
the same method resistant strains of a Cuban variety (Little
Cuba), a variety (Dubek) from Russia, and a variety (Santi-
ago) from Java have been developed, but none of these varieties

"Tisdale, W. B., and J. G. Kelley. Loc. Cit.
'Tisdale, W. B. Progress in the control of black shank of tobacco through
disease resistance, (Abstract) Phytopath., 19:93. 1929.







Florida Agricultural Experiment Station


is satisfactory for growing under local conditions. On the other
hand, no progress has been made in the development of resistant
strains of the variety known as Connecticut Round Tip and sev-
eral others which possess desirable quality for cigar wrappers,
as no individuals survived on uniformly infested soil.
Connecticut Round Tip was introduced from Connecticut into
Florida in 1921 and from the first the yield and quality of leaf
produced proved superior to the local variety, Big Cuba. Im-
mediately, the acreage of the Round Tip was increased and that
of Big Cuba was decreased in proportion until in 1924 practically
the entire acreage was planted to Round Tip. This general
planting of Connecticut Round Tip was concomitant with a
severe epidemic of blackshank which resulted in a complete
failure of the crop in many fields and a very heavy reduction in
yield for the entire district. This disastrous epidemic of black-
shank convinced the growers that it was very hazardous to make
further attempts to grow Connecticut Round Tip on old shade
lands. Many growers planted the crop under cloth shade on new
land each year, but the quality of leaf proved less desirable in
many cases and the crop did not always escape loss from the dis-
ease. Since a market had been created for the Connecticut Round
Tip type and quality of leaf, the jobber and manufacturer offered
the grower no encouragement to return to the Big Cuba type.
Therefore, the problem presented was to secure a resistant strain
which would produce a good yield of leaf that would meet the
demands of the trade. The greatest possibility for accomplish-
ing this result seemed to lie in crossing the resistant strains of
mediocre quality of leaf or low yield with susceptible strains of
good yield and superior quality of leaf.

METHODS OF EXPERIMENTATION

Tobacco blossoms are self-pollinated but when grown in the
open they may be cross-pollinated by insects and humming birds.
Therefore, in selecting plants to perpetuate certain characters,
it is only necessary to protect the blossoms from cross-pollina-
tion. This was conveniently done by covering the inflorescence
with a 12-pound sulphite paper bag until the seed were mature.
As a rule, fewer seed were obtained from plants thus treated
than from unbagged plants, but in most instances ample
seed were obtained from each plant for extensive tests. There
was no apparent reduction in vigor of the plants resulting from







Bull. 226, Development of Resistant Cigar Tobaccos 7

selling, even though some strains had been selfed repeatedly for
eight generations. However, there were some deviations in
growth habits from the commercial variety. One of the chief
reasons for these deviations probably is that the commercial
varieties are usually not uniform for leaf characters and the
disease reduced the plants to a very small group within which
the original selections were made, thus leaving little opportunity
to select for conformity to the original predominant type of the
commercial variety.
The initial selections of Big Cuba were made in a commercial
field in which blackshank was very severe. Seed from each self-
pollinated plant were saved separately and planted the following
season on a steam-sterilized bed. A 6-inch board was placed on
edge between adjacent lots of seed to prevent mixing. Seedlings
from each lot were transplanted to thoroughly infested soil in
adjacent rows. Seed of the best plants from the most resistant
rows were again saved and the process was repeated until a
highly resistant strain was developed. Except for certain de-
tails, this method was employed with the progenies resulting
from crosses.
In all the work, plants as near the same size as possible were
used for field trial and whenever possible all strains tested in one
field were transplanted on the same day. Whenever the number
of plants was sufficient, the tests were duplicated each year on
two different fields. The soils used in the trials belonged to the
Norfolk and Tifton series and in most cases the plots were lo-
cated on both types each year. The land was fertilized and cul-
tivated according to general practices. Rows of the commercial
Big Cuba or Connecticut Round Tip variety were planted across
the field at intervals for checks. The prevalence of blackshank
among the selections was recorded at intervals of 10 to 14 days
throughout the growing season. External condition of the plants
above ground only was used to determine the percentage of
blackshank during the growing season. After the first year one
or two primings of leaves were kept from the most resistant
selections for comparing quality. This made possible the elim-
ination of the strains unsuited for cigar wrappers.
The results obtained on the two fields in any one year did not
always check, although the selections which were most resistant
in one field usually showed highest resistance in the other. The
results shown in the tables are the average of the results obtained
in the two fields.






Florida Agricultural Experiment Station


A very simple and easy method was used in making crosses.
Some of the first blossoms which appeared were used for most
of the crosses. The emasculating and pollinating operations
were performed on the day before the blossoms were ready to
open. Pollen from blossoms of the same stage of development
as the ones pollinated was used. At that time the anthers were
not ruptured but the pollen was mature and could be removed
easily and applied to the stigma with a sharp pointed scalpel or
forceps. This method was very successful and required the min-
imal time for the operation. Pollen from blossoms one day older
gave equally successful results, but there was danger of obtain-
ing mixed pollen unless the blossoms had been bagged previously.
The cross-pollinated blossoms were protected with a bag which
was left in place until the seed were harvested. In order to
expedite the work the Fi plants, except those from the first cross,
were grown in the greenhouse during the winter months on
steam-sterilized soil. The F and subsequent generations were
tested in the field on thoroughly infested soil, except in one or
two instances, as indicated in the text, a few plants were grown
in the greenhouse during the winter.
As a rule, several different types of plants appeared in the sec-
ond generation, and in some cases the individuals which ap-
parently possessed the most desirable leaf characters succumbed
to the disease before they reached maturity. In practically every
instance some of the F plants began to show signs of the dis-
ease within a few weeks after transplanting, while others suc-
cumbed at intervals throughout the growing season. Many
plants which showed no signs of the disease during the growing
season were found to have part of the root system dead when the
seed were harvested. In most instances of this nature, infec-
tion appeared to have developed after the plants were mature.
The root systems of all selected plants were examined at the
time the seed were harvested and, as a rule, seed were saved for
further trial only from those which showed no root infection.
Whenever a plant was outstanding for desirable leaf characters,
seed were saved from it, even though part of the roots were dis-
eased. The progenies of several such plants proved as resistant
as those of plants with healthy root systems.
No effort has been made to study the ratio of inheritance of
the resistant character since, at the time most of the crosses
were made, it was apparent that none of the parent strains used
were homozygous for the resistant character. Because of the






Bull. 226, Development of Resistant Cigar Tobaccos 9

urgent demand for a resistant strain or variety of the cigar
wrapper type, special consideration has been given to the in-
dividuals and their progenies which showed greatest promise in
this respect. Progenies of crosses which possessed undesirable
qualities for cigar wrappers were discarded as soon as the quality
could be determined, even though they were highly resistant.

RESISTANT STRAINS FROM COMMERCIAL VARIETIES

Since the beginning of the work, seed of different varieties
of tobacco grown in the United States and many from several
foreign countries have been obtained from time to time and
tested on infested soil. These included varieties of virtually all
of the different commercial types of Micotiana tabacum Linn.,
one wild variety from Guatemala and one from Matacumbe Key,
Florida, and one variety of Nicotiana rustica Linn. These tests
were conducted in an effort to determine whether any resistant
varieties existed in nature so they might be used as a basis,
through crossing, for developing a resistant strain suitable for
cigar wrappers when grown under local conditions.
Nicotiana rustic proved highly resistant from the beginning.
On the other hand most of the varieties of Nicotiana tabacum
tested, except the ones from which resistant strains have been
obtained and discussed in this paper, were almost completely
susceptible. All efforts to cross Nicotiana rustica with varieties
of Nicotiana tabacum were unsuccessful. With certain varieties
of Nicotiana tabacum a few plants remained healthy in the first
test but their progenies succumbed when planted on infested soil,
showing that the few plants merely escaped infection the first
year. On the other hand, an occasional plant of the local variety
Big Cuba, Little Cuba (Cuban), and Santiago (Java) remained
healthy on infested soil throughout the season and the progenies
of several of these selfed individuals showed increased resistance
in the first and subsequent generations. However, completely
resistant strains of these varieties have not been obtained after
selecting for several years, although several of the strains
showed no symptoms of disease until the approach of harvest
season. The susceptible varieties used as checks usually showed
100 percent blackshank before that time.







Florida Agricultural Experiment Station


BIG CUBA
The Big Cuba variety of cigar wrapper tobacco is said to have
originated from a cross between Sumatra and Cuban varieties
which were grown extensively in Gadsden County before 1900. It
was the main variety grown under shade from about 1909 to
1923. Many of the growers had saved their own seed from year to
year and as a result there were noticeable differences in the color,
size, and number of leaves among the strains from different
farms. In order to facilitate the identification of selections
from different sources they were given different stock numbers.
Thus, the letter, as A, E, H, P and Se, in the progeny number
represents the source of the selection. The first number, as
22, represents the year the seed was saved and the third number
is the number of the individual plant in the series.
The initial selections of Big Cuba for resistance were made
in 1922 in two commercial fields in which blackshank was very
severe and uniformly distributed. Also, four plants were se-
lected on non-infested soil that year because they showed out-
standing leaf characters. The progenies of these selected plants
were tested for resistance to blackshank in 1923 in infested
soil. A report of the first three years' results with these selec-
tions is given in a previous publication" but in order to show the
general progress in the development of resistant strains, they
are included in Table I with the data obtained through 1930.
The relative resistance and general characters of growth of
this resistant strain may be seen in Fig. 1. The leaf characters
are quite uniform, although they differ in certain details from the
commercial variety of Big Cuba from which it was developed.
As may be seen in Fig. 2', the angle formed by the lateral veins
and midrib is almost a right angle. It has been reported that
leaves possessing this character cannot be stripped satisfactorily
by machinery. Another objection which has been given by cigar
manufacturers against Big Cuba and the resistant strain is that
the cured leaf is sleazy and breaks badly after it is wrapped on
cigars. Because of these two undesirable characters there is
only a small demand for Big Cuba tobacco. However, the quality
of the resistant strain appears as good as that of the commercial
variety when grown under similar conditions.

'Tisdale, W. B., and J. G. Kelley. Loc. Cit.
"All pictures used in this bulletin to illustrate leaf characters were made
on the same scale.







Bull. 226, Development of Resistant Cigar Tobaccos


Fig. 1.-Resistant Big Cuba tobacco (left and right) and susceptible Con-
necticut Round Tip (center) in Phytophthora-infested soil in 1927.
Photographed after most of the leaves had been harvested.


PIG ClUf-,


Fig. 2.-The fifth (left) and tenth leaves from a plant of the resistant
strain P of Big Cuba tobacco. Note that angle formed by lateral
veins and midrib is almost a right angle.


M-:*








Florida Agricultural Experiment Station


TABLE I-OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES OF STRAINS
SELECTED FROM THE BIG CUBA VARIETY OF TOBACCO WHEN GROWN IN
INFESTED SOIL.
S Condition at End of Season
SNo. of
Generation Progeny Number Plants Healthyl Diseased
Tested Percent Living Dead
S Percent Percent
1923

Commercial Stock.. Big Cuba (check) 520 18 59 23
First....................I P-22- 1 ................. 456 6 64 30
P-22- 3 ............... 112 81 14 5
P-22- 4 ............- 43 88 12 0
E-22- 2 .....---....-- 431 74 21 5
E-22- 3 .................. 71 5 61 34
E-22- 4 .................. 148 7 40 53
E-22- 6 .................- 61 23 66 11
E-22-10 .................. 287 35 33 32

SE-22-14 .................. 400 76 17 7
SE-22-15 .................. 58 7 55 38
SE-22-16 .................. 150 15 53 32
I E-22-18 .................. 113 15 65 20
SE-22-19 ................. 62 14 37 49

SE-22-21 .................. 457 42 35 23
E-22-22 ................. 62 39 42 19
E-22-24 .................. 64 7 45 48
E-22-27 .................- 607 29 38 33
E-22-28 .................. 376 9 47 44

E-22-34 ................. 278 15 51 34
E-22-35 ....-............. 84 90 5 5
E-22-36 ................ 259 8 52 40

A-22- 5* ..... ...... 64 88 10 2
A-22-22" ............... 96 0 40 60
H-22-16* ............... 153 72 18 10
SSe-22-12* ............. 28 61 32 7

*These selections were made on uninfested soil.
1924

Commercial Stock.. Big Cuba (check) 586 4 3 93
Second....--..........- I P-23- 1 ........ |. 157 23 4 73
P-23- 4 .................. 205 34 2 64
P-23- 6 ................. 180 36 12 52
P-23- 8 .................. 154 26 7 67
P-23- 9 .................. 96 34 0 66

I P-23-10 ..-..--....-... 178 30 8 62
P-23-11 ................ 179 43 7 50
I I 1
A-23- 3 ....... ...... 205 19 3 78
A-23- 4 ........._.. 177 12 7 81
SA-23-16 .................. 229 0 3 97
I








Bull. 226, Development of Resistant Cigar Tobaccos 13

TABLE I-OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES OF STRAINS
SELECTED FROM THE BIG CUBA VARIETY OF TOBACCO WHEN GROWN IN
INFESTED SoIL.-Continued


Generation Progeny Number I


SHo-23-1 ..............I
Se-23-3 ...............
H1-23- 2 .......-....---
H-23- 3 ........

E-23- 2 ................
E-23- 4 ..............
SE-23- 8 ................
E-23-14 ............
E-23-15 .............

E-23-16 ..................
E-23-21 ..............
E-23-27 .................
SE-23-34 ...............
E-23-42 .................
E-23-43 ................


i
I


Commercial Stock.. Big Cuba (check)
Third............. P-24- 1 .........
IP-24- 3 .. ...
P-24- 6 ............
SP-24- 8 .......... .....

P-24-19 .. .........
P-24-32 ...... ..........
P-24-33 .................
P-24-41 ............
P-24-44 ... ...

P-24-51 ...... ....... .
SP-24-52 ...............
SP-24-54 ............
P-24-61 .. ...

E-24- 1 ..........
E-24- 2 ..............
E-24- 6 ..................
I E-24- 7 ..................
E-24-22 7 .......
A-24-22 |
SA-24-24 ............
SA-24-26 ..................
I A-24-27 ...............
A-24-30 .- ....
SA-24-35 -.........
SA -24-36 ...... ..........

SH -24- 1 ..................
SH -24- 8 .................


SCondition at End of Season
No. of I
Plants Healthy Diseased
Tested percent ILiving Dead
Percent Percent
151 23 6 71
209 4 3 93
211 1 2 97
215 8 0 92

164 12 5 83
175 5 3 92
165 10 5 85
211 10 2 88
178 8 6 86

170 16 2 82
167 3 2 95
120 5 3 92
186 11 4 85
166 1 0 2 98
178 3 2 95







Florida Agricultural Experiment Station


TABLE I-OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES OF STRAINS
SELECTED FROM THE BIG CUBA VARIETY OF TOBACCO WHEN GROWN IN
INFESTED SoIL.-Continued

| I Condition at End of Season
SNo. of _
Generation Progeny Number I Plants Healthy Diseased
STested Percent Living Dead
SPercent Percent

Fourth.............. P-25-3* ................. 111 57 16 27
P-25-4* ................ 296 56 12 32
P-25-5* ........-........ 290 63 14 23
I P-25-8* .................. 241 54 11 35
P-25-10* ............ 148 56 18 26
P-25-11* ............. 221 70 14 16
SP-25-12* ............. 212 56 19 25
SP-25-14* ................ 106 42 8 50

*Parents of these selections were grown in greenhouse during winter
of 1924-25 in sterilized soil from seed of progeny P-24-1 and P-24-4.

1926

Commercial Stock.. Big Cuba (check) 225 2 4 94
Fifth................. P-26-1 ................. 95 84 4 12
P-26- 2 .................. 215 62 4 34
P-26- 3 ........... 203 46 6 48
P-26- 4 ................. 204 4 2 94
) P-26- 5 ................ 203 72 7 21
IP-26- 7 ............- 90 80 4 16
IP-26- 9 ......... ......... 208 70 11 19
SP-26-12 ............. 205 63 15 22
1 P-26-13 ............- 209 65 9 26
P-26-23 ............ 96 70 6 24

1927

Commercial Stock. Conn. Round Tip
S (check) .............. 282 0 0 100
Sixth ........---- ....I P-27- 5 --..-..--- ..... 500 69 11 20
IP-27- 7 .................. 471 71 9 20
P-27- 9 ........... 95 98 1 1
P-27-10 ..----- 477 82 0 18
P-27-13 ................ 478 74 8 18
P-27-15 ..........- 464 86 2 12

1928

Commercial Stock.. Conn. Round Tip
(check) ............. 662 0 2 98
Seventh............... P-27-20 ................ 73 93 4 3
P-27-23 ............... 73 97 0 3
P-27-26 .................. 277 94 0 6







Bull. 226, Development of Resistant Cigar Tobaccos 15

TABLE I.-OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES OF STRAINS
SELECTED FROM THE BIG CUBA VARIETY OF TOBACCO WHEN GROWN IN
INFESTED SOIL.-Continued


Generation IProgeny


P-27-27
IP-27-29
P-27-32
P-27-33
[ P-27-37
P-27-38
SP-27-39
SP-27-40
SP-27-41


Number


I Condition at End of Season
No. of I
SPlants IHealthy I Diseased
Tested Percent Living Dead
S Percent Percent

S 212 88 2 10
S 226 90 4 6
S 125 94 2 4
.1 66 95 0 5
S 170 92 6 2
94 93 4 3
S 106 100 0 0
S 79 89 2 9
99 95 5 0


Commercial Stock..l Conn. Round Tip
I (check) ............ 273 0 0 100
Eighth............ P-28- 2 ................. 70 99 1 0
P-28- 4 ..... ....... 89 89 9 2
1P-28-10 ............- 203 87 7 6
SP-28-11 .................. 109 92 2 6
I P-28-14 ................ 197 90 5 5
I P-28-15 --..........-.... 206 90 4 6
P-28-17 .................. 203 90 8 2

1930

Ninth... ......-..... P-29- 2 ............... 60 72 18 10
[ P-29- 5 --.... 65 65 20 15


It may be observed from the results given in Table I that the
progress made in the isolation of resistant strains of the Big
Cuba variety was very gradual. Also, there was some variation
in the degree of resistance from year to year after the fifth
generation. This was especially noticeable in 1930 when the
two selections tested showed much lower resistance than in 1928
or in 1929. It so happened that the rainfall was light and pre-
vailing temperatures were high during the growing season of
1930. The same conditions existed in 1925. However, none of
the strains had shown a high degree of resistance prior to 1925.
It is possible, therefore, that the unfavorable conditions for
growth of the tobacco plant also exerted an injurious effect upon
the resistant character. This theory is supported by the high






Florida Agricultural Experiment Station


percentage of plants which showed symptoms of the disease in
those years but were not killed.
It may be observed also that all of the original selections ex-
cept those from one source were dropped after the third year.
Other selections were made in commercial fields from time to
time but in most cases their progenies showed either little or
no resistance or inferior quality of leaf, and the results of the
tests are not shown.
LITTLE CUBA
This variety of tobacco was originally introduced from Cuba
and was grown extensively in the State until the development of
artificial shade in 1896. The quality of leaf of this variety is
considered very good, but on account of the small number and
size of leaves, resulting in low yield, it could not be grown profit-
ably under shade and its culture was discontinued except on small
acreages. Although this variety had been grown in the State
for years and
propagated from
m a s s selected
seed, it was fair-
ly uniform for
leaf characters.
The original
selections of Lit-
tle Cuba for re-
sistance to black-
shank were made
in 1923 in a 5-
acre commercial
field i n which
there were evi-
dences of only
slight blackshank
Fig. 3.-The fifth (left) and tenth leaves from a infection. T h e
plant of resistant Little Cuba tobacco. Note
that angle formed by lateral veins and midrib progeny of one of
is slightly more acute than that of resistant Big t h e s e selected
Cuba.
plants was tested
on infested soil in 1924. At the end of the season 80 percent of
the plants were living and 50 percent were healthy.
Several selections were made from this strain but only two
of them were tested in 1925. The tests were made on two farms







Bull. 226, Development of Resistant Cigar Tobaccos 17

and in each case both selections showed a high percentage resist-
ance to blackshank, averaging 85 percent living and 74 percent
healthy.
The trials of this strain in 1926 included a similar Cuban
variety (Havanensis), the seed of which was obtained from
Cuba in the summer of 1925. Several selections were tested that
year in the same field used in 1925. The results of these trials
and those obtained in 1927 are shown in Table II. The general
leaf characters of this variety are shown in Fig. 3.
TABLE II.-OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES OF STRAINS
SELECTED FROM THE "LITTLE CUBA" VARIETY OF TOBACCO WHEN GROWN
IN INFESTED SOIL.

I Condition at End of Season
SNo. of I
Generation Progeny No. I Plants Healthy I Diseased
I Tested Percent Living Dead
I I Percent I Percent
1926

Commercial Stock...! Big Cuba (check) I 512 4 1 2 94
Commercial Stock... Havanensis .......... 149 68 5 27
Third........................ L. C. 25- 1 ............. 199 67 1 3 30
L. C. 25- 3 ........... 105 43 5 52
L. C. 25- 4 ........-... 211 75 2 23
L. C. 25- 6............. 202 65 5 30
L. C. 25- 7.............. 214 58 1 10 32
L. C. 25- 8.............. 153 66 I 7 27
L. C. 25-10.............. 148 54 8 38
L. C. 25-11........... 200 47 4 49
L. C. 25-12............ 109 20 1 7 73
L. C. 25-13............. 210 71 6 23

1927

Commercial Stock.. Conn. Round Tip ]
S (check) ............I 319 0 0 100
Second......................- Hav. 26- 2..............j 178 85 4 11
SHav. 26- 3..............1 125 90 5 5
Fourth.................. L. ........... L.C. ........ 72 83 3 14
L. C. 26-12 ............ 73 88 1 11
________________________ I
Only one of the resistant strains of the Little Cuba variety was
planted each year after 1927 because of the small number and
size of the leaves. It was planted to cross with certain other
varieties.
SANTIAGO (JAVA)
In 1927 seeds of several varieties of tobacco were obtained
from Java through the United States Bureau of Plant Intro-






Florida Agricultural Experiment Station


duction. Plants of these varieties were tested on blackshank-
infested soil in the summer and fall of that year. All varieties
except Santiago proved completely susceptible to the disease
and only two plants of that variety remained healthy and vig-
orous. These two plants were self-pollinated and their progenies
when tested on infested soil in 1928 showed 78 and 84 percent
healthy plants, respectively, at the end of the season. Three
plants which possessed the largest leaves were selected from the
most resistant strain and their progenies were tested in 1929 on
infested soil. At the end of that season two of the strains
showed 96 percent healthy plants and the third one 94 percent.
Although this variety produced a leaf which possessed fair
quality for cigar wrappers, it was considered unprofitable to
grow under Florida conditions because of the small number and
size of the leaves and no further tests were made. However, it
was crossed with other varieties in an effort to combine its re-
sistance with larger leaves.
DUBEK (RUSSIA)
In 1926 seeds of several varieties of tobacco were obtained
from Russia and they were planted in infested soil in 1927. Most
of them resembled Turkish varieties but no information was
supplied concerning their origin or purpose for which grown.
All of these varieties, except Dubek, succumbed very quickly to
blackshank. At the end of the season 78 percent of the plants
of Dubek were living and 66 percent of them were healthy.
Although the variety showed no possibilities for cigar wrappers,
a few of the plants were self-pollinated and the progeny of one
of them was tested on infested soil in 1928. This selected strain
proved very resistant to blackshank; 100 percent of the plants
were living and 96 percent were healthy at the end of the season.
The leaf characters were very uniform and the average number
of leaves per plant was 32. Since the leaves were entirely too
small for cigar wrappers, the strain was not given further trial.
However, it has been crossed with other varieties and the prog-
enies are being tested for resistance and quality of leaf.
RESISTANT STRAINS FROM CROSSES
During the course of these studies numerous crosses have been
made between several different varieties and strains of tobacco.
The progenies of several of the earlier crosses were either com-
pletely susceptible to blackshank or the quality of the leaf was






Bull. 226, Development of Resistant Cigar Tobaccos 19

not suitable for cigar wrappers. The tests of such strains ex-
tended over a period of from one to four years only. Further-
more, several crosses have been made during recent years but
the progenies have not been tested sufficiently to determine their
resistance to blackshank and quality of leaf. Consequently, re-
sults of the tests with such strains are not included in this report.
Only the resistant strains which have shown some possibility for
cigar wrappers are discussed. Although most of these strains
have been grown commercially to some extent and certain ones
have proved fairly satisfactory for resistance and quality, the
tests have not been made over a sufficient number of years to
warrant the recommendation of any particular strain. Fur-
thermore, the showing made by progenies of some of the more
recent crosses indicates that they may be superior to the resist-
ant strains now in commercial use and will supersede them as
soon as their value can be established. None of the strains has
been given a variety name, and all are discussed under the num-
ber used to designate the Fi, as Nos. 1, 94, and 301.

NO. 1
The first artificial crosses in connection with the experiments
herein reported were made in 1923 between Big Cuba and Con-
necticut Round Tip. In these crosses Big Cuba was the male
parent and Connecticut Round Tip the female. The Big Cuba
plants used in the crosses were growing on infested soil and were
individuals of the most resistant strain tested that year. The
Connecticut Round Tip was growing on uninfested soil. Ten
crosses were made and the hybrid seed were assigned the num-
bers 1 to 10", inclusive.
The F1 progenies of these crosses were tested in 1924 in the
field in thoroughly infested soil. All plants from eight of the
crosses succumbed to the disease and only a few plants of the re-
maining two, numbers 1 and 6, survived. These plants were
self-pollinated and the F. progenies were tested on infested soil
in 1925. Although the percentage resistance of the F2 was low,
seed were saved from the few healthy plants for testing the F,

"Throughout this paper the initial figure, as 1, 6, and 94, of the progeny
number designates the number assigned to the hybrid seed for the F1 plants.
Later generations appear as 1-1, 6-1 and 94-1 for F2 and 1-1-1 to 1-1-3 or
as many individuals as were selected in the series for Fa. Each year the
progeny number increases by one figure, the figure being appended on the
right. By this method the progeny number indicates the generation of the
plants being grown.







Florida Agricultural Experiment Station


progeny. Seed from one of the F2 selections were planted in the
greenhouse during the winter of that year, and the progeny of
one of the greenhouse plants was tested in 1926 alongside of
sister strains of the parent. The results of these and succeeding
trials are shown in Table III.

TABLE III.-OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES FROM
CROSSES BETWEEN A RESISTANT STRAIN OF BIG CUBA AND SUSCEPTIBLE
CONNECTICUT ROUND TIP TOBACCO PLANTS WHEN GROWN IN THE FIELD
IN INFESTED SOIL.


Generation Progeny


Commercial Stock...
Second....................


Condition at End of Season
INo. of I
Number IPlants I Healthy I Diseased
Tested J Percent I Living ] Dead
IPercent I Percent


Big Cuba (check)
1-1 ............ ............
6-1 -----------
6-3 .....-.......
Conn. Round Tip
(check) .............


1926


Commercial Stock..
Tvhi; A


I
Conn. Round Tipl
(check) ..............
1_1-1


204 0 0 100
127 41 19 40


r ---------------------.I.----------- --.. .......
1-1-3 -- 153 25 8 67
1-1-3g* ...------..... 208 36 6 58
S6-1-1 .. .... 217 31 4 65

*Parent of this strain was grown in greenhouse during winter of 1925-
26. In this case the letter "g" was added instead of another generation
number.


Commercial Stock...

Fourth-..................---.


Conn. Round Tip
(check) .............. 319 0
1-1-2-1** ............ 215 0
1-1-3-1 .........-- 122 42
1-1-3-4 .........----- 82 43
1-1-3-5 ...........--.---. 127 59

1-1-3g-1 --..--- -- 112 48
1-1-3g-2 .-.---- 120 64
1-1-3g-4 .............. 71 77
1-1-3g-5 ------ -- 204 83
6-1-1-1 ............. 194 82
6-3-2-1 .................. 199 39


**Parent of this strain was grown in greenhouse
1926-27.


during winter of


I ~


I






Bull. 226, Development of Resistant Cigar Tobaccos 21

TABLE III.-OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES FROM
CROSSES BETWEEN A RESISTANT STRAIN OF BIG CUBA AND SUSCEPTIBLE
CONNECTICUT ROUND TIP TOBACCO PLANTS WHEN GROWN IN THE FIELD
IN INFESTED SOIL-Continued.

I Condition at End of Season
No. of I
Generation Progeny Number I Plants Healthy Diseased
I Tested Percent I Living IDead
I Percent Percent
1928

Commercial Stock..I Conn. Round Tip!
S (check) ............ 212 0 5 95
Fifth.....-.............- ... 1-1-3-4-1 ........ 46 98 0 2
1-1-3-5-2 ................ 108 92 2 6
1-1-3-5-6 ..-..........- 84 73 3 24
1-1-3g-5-3 ............. 25 100 0 0
1-1-3g-5-4 .............. 92 96 0 4
6-1-1-1-1 ...... 264 89 4 7
S6-3-2-1-1 ............... 187 68 | 14 18
I 6-3-2-1-2 ............... 160 33 | 34 33
I 6-3-2-1-3 ........-....... 160 39 37 24
I 6-3-2-1-5 ................ 148 65 10 25

1929

Commercial Stock._. Conn. Round Tip
| (check) .................. 273 0 0 100
Sixth-- -............ ..- .... 1-1-3g-5-4-1 .......... 201 95 1 4
S1-1-3g-5-4-2 ..... 197 98 1 i 1
1-1-3g-5-4-3 ...... 202 98 0 2
1-1-3g-5-4-4 ......... 193 99 0 1

i 6-3-2-1-1-1 ............ 35 94 0 6
i 6-3-2-1-2-1 ............ 44 89 11 0
6-3-2-1-5-2 ............ 80 1 100 0 0
S6-3-2-1-5-3 .------- 31 | 100 0 0
I 6-3-2-1-5-4 ..-......... 114 93 0 7

1930

Commercial Stock... Conn. Round Tip I
I (check) .............. 333 0 0 100
Seventh.................... 1-1-3g-5-4-2-3 ...... 65 86 12 2
S1-1-3g-5-4-2-4 ......- 66 92 3 5
S1-1-3g-5-4-4-1 ...... 64 83 10 7
1-1-3g-5-4-4-2 ...... 64 91 0 9


As may be seen from Table III, many of the Fs and Fe selec-
tions of No. 1 were practically 100 percent resistant to black-
shank in 1928 and in 1929 (Fig. 4), but all of the F, selections
tested in 1930 showed some susceptible plants. It is also notice-
able that there was no sudden segregation into resistant and






Florida Agricultural Experiment Station


susceptible strains, but rather a gradual increase in degree of
resistance from year to year. The F. and F. selections from
these crosses appeared very uniform for leaf characters and
there were only slight differences in leaf characters between the
sister selections of each cross. However, there were marked
differences in the leaf characters between the No. 1 and No. 6
strains. The leaves of the No. 6 strain were unsuited for cigar
wrappers, because they were narrow in proportion to the length
and strongly tapered toward each end and when cured the color
was dark. The leaves of the No. 1 strain are considerably larger
than either parent when grown under similar conditions, but the
general shape and venation of the leaf are intermediate between
the two (compare figures 2, 5, and 6). The strain averages only
21 leaves per plant, but the large size of the leaves insures a
heavy yield. The leaf is thin and light colored when cured, but
the veins are somewhat coarse, as would be expected from the
size of the leaf.


Fig. 4.-Two selections of the resistant strain No. 1 in Phytophthora-in-
fested soil in 1929. Photographed after about one-third of the leaves
had been harvested.
This No. 1 strain was tested on a small commercial scale for
the first time in 1930. The yield and color of the cured leaf was
reported as being fairly satisfactory, but it was reported to have






Bull. 226, Development of Resistant Cigar Tobaccos 23

a coarse texture and an unusually bitter taste. The strain will
be tested further to determine whether this bitter principle is an
inherent character. If this should be the case, the strain would
be worthless for cigar wrappers.





















Fig. 5.-The fifth (left) and tenth leaves from a plant of Connecticut
Round Tip tobacco. The acute angle formed by the lateral veins and
midrib of this variety is said to be very desirable.
R
In 1924 the owner of a farm on which one of the test plots was
located set one row-325 plants-of Connecticut Round Tip
through perforated mulch paper. This row was adjacent to a
row of partially resistant Big Cuba. The mulch paper appeared
to have no effect whatever on the rate of development of black-
shank, since all of the plants were dead by the end of the season.
However, one plant matured some seed before it died. The
leaves of this plant were typical of the Connecticut Round Tip
variety, as far as was determined. The seed were saved and
assigned the letter R to designate it as a selection of Connecticut
Round Tip. The inflorescence had not been bagged.
In 1925, 224 plants from this selection were tested in the
field for resistance to blackshank. By the time the plants had
attained a height of one foot it was evident that only a few of
them possessed characters typical of the Connecticut Round Tip






Florida Agricultural Experiment Station


variety. The others possessed leaf characters somewhat similar
to Big Cuba. This was especially true of the upper leaves of the
mature plants. As the season advanced the plants which most
closely resembled Connecticut Round Tip succumbed to black-
shank, while a number of the others remained healthy and vig-
orous. At the end of the season 54 percent of the 224 plants were
living and 45 percent were healthy. Therefore, it was assumed
that the plant was pollinated with pollen from the partially re-


Fig. 6.-The fifth (left) and tenth leaves from a plant of the resistant
strain No. 1. The angle formed by the lateral veins and the midrib
is slightly less acute than that of the Connecticut Round Tip variety.

sistant strain of Big Cuba growing adjacent to it in 1924. This
assumption was supported in 1926 by the fact that typical Big
Cuba plants appeared in the FZ progeny of one of the selected
seed plants. Several selections of the strain were grown in the
F= in 1926 and in succeeding generations successively through
1930 in infested soil and the results are shown in Table IV. This
strain was numbered and handled as a selection instead of a
cross because nothing definite was known concerning the pollina-
tion.







Bull. 226, Development of Resistant Cigar Tobaccos 25

TABLE IV.-OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES FROM A
PROBABLE NATURAL CROSS BETWEEN PARTIALLY RESISTANT BIG CUBA AND
SUSCEPTIBLE CONNECTICUT ROUND TIP TOBACCO PLANTS WHEN GROWN
IN THE FIELD IN INFESTED SOIL.


Generation Progeny Number


Commercial Stock...

Second......... ......


Condition at End of Season
No. of I
Plants Healthy I Diseased
Tested Percent Living Dead
SIPercent Percent


Conn. Round Tip
(check) -.. ... 258 0 1 99
R-25-1 .................. 71 90 0 10
R-25-2 .............. 204 44 6 50
R-25-3 ......... ..... 210 76 1 23
R-25-4 ...... ........... 150 76 1 23
______ I I


Commercial Stock...'

Third ........---........


Conn. Round
(check) ....
R-26-1 ....
R-26-2 ..........
R-26-3 .......
R-26-4 .......
R-26-6 ........
R-26- 7 -
R-26- 9 .......
R-26-13 ........
R-26-15 .........
R-26-16 .--
R-26-20 ......

R-26-21 .......
R-26-22 .......
R-26-24 .......
R-26-25 ........
R-26-26 .........


Tip










....----..
........I


1928

Commercial Stock I Conn. Round Tip
S (check) ......... 662 0 2 98
Fourth...................... R-27-lg* .- 116 80 11 9
R-27-6g* ............ 100 73 14 13
IR-27-8g* ........... 25 100 0 0

R-27-2 ................. 238 85 4 11
SR-27-5 ....-.............. 42 95 | 0 5
R-27-7 ......-..........- 80 87 1 12
SR-27-8 ................... 81 89 0 11
R-27-9 ...... .............. 78 73 0 27


*Parents of these strains were grown
of 1927-28.


in greenhouse during the winter


Commercial Stock...!

Third ........................







26 Florida Agricultural Experiment Station

TABLE IV.-OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES FROM A
PROBABLE NATURAL CROSS BETWEEN PARTIALLY RESISTANT BIG CUBA AND
SUSCEPTIBLE CONNECTICUT ROUND TIP TOBACCO PLANTS WHEN GROWN
IN THE FIELD IN INFESTED SIL-Continued.


Generation


Progeny No.


1R-27-12
R-27-14
R-27-16
R-27-17
R-27-19

R-27-20
R-27-23
R-27-26
R-27-28
R-27-29

R-27-31
R-27-35
R-27-38
R-27-39
R-27-40


No. of
Plants
Tested


271
39
92
58
154

126
137
46
78
92

138
172
74
220
279


Condition at End of Season

Healthy I Diseased
Percent I Living Dead
I Percent I Percent

94 0 6
90 0 10
89 6 5
95 3 2
72 5 23

75 0 25
90 1 9
89 0 11
67 0 33
84 0 16

92 1 7
84 1 15
77 3 20
92 3 5
82 10 8


1929

Commercial Stock... Conn. Round Tip
(check) .............. 96 0 4 96
Fifth........................ -28-1 ...... .. 51 65 15 20
R-28-2 .................... 65 83 9 8
R-28-3 .......--....-----. 47 81 12 7
1 -28-4 .--................ 82 70 21 9

R-28-10 .................. 97 88 5 7
R-28-12 .................. 254 94 0 6
R-28-13 .................. 164 92 7 1
SR-28-14 .................. 55 95 3 2
SR-28-15 ....----.............. 124 81 9 10

1930

Sixth.....................-- ..- R-29- 1 ....-- .... 135 61 7 32
I R-29-10 .-............... 253 78 4 18
I R-29-11 ................. --- 262 72 7 21
I R-29-15 ....-....--..-----....... ----256 78 3 19






Bull. 226, Development of Resistant Cigar Tobaccos 27

It may be observed from Table IV that certain selections of R
were highly resistant to blackshank in 1928 and in 1929 and that
these resistant selections were obtained in a shorter period of
time than was required to obtain a resistant strain from the
No. 1 cross discussed previously. The leaf characters are shown
in Fig. 7 and the growth characters in infested soil are shown
in Fig. 8. In many respects the leaves resemble Connecticut
Round Tip, the main differences being that the leaf is broader at
the "heel"; the lateral veins form a little more acute angle with
the midrib and the leaf is a little broader in proportion to the
length. This strain was tested on a small commercial scale in
1929 and 1930. The quality of leaf proved very good under
slat and combination shade but was not so good under cloth alone.


Fig. 7.-The fifth (left) and tenth leaves from a plant of the resistant
strain R. Note that the leaves are broad in proportion to length and
that the angle formed by the lateral veins and midrib is more acute
than that of the Connecticut Round Tip variety.
301
The first crosses between Big Cuba and Little Cuba were made
in 1924. The strain of Big Cuba used in the crosses was an FL
progeny of the selfed selection made in 1922, which was growing
on infested soil. Only 48 percent of the plants of this strain re-
mained healthy until the end of that season. The strain of Little






Florida Agricultural Experiment Station


Fig. 8.-The resistant strain R (left) and susceptible Connecticut Round
Tip (right) on Phytophthora-infested soil in 1929. Photographed after
the first three or four leaves had been harvested.

Cuba used in the crosses had been self-pollinated and tested on
infested soil for one year only, and at the end of the season 80
percent of the plants were living and 50 percent were healthy.
The individuals of each strain used in the crosses were selected
for vigor and desirable leaf characters. Reciprocal crosses were
made between the two strains, different individuals being used
for each cross. Four crosses were made, with Big Cuba as the
female parent in two and Little Cuba in two. The hybrid seed
of which Big Cuba was the female parent were given the num-
bers 301 and 303, and those in which Little Cuba was the female
parent were numbered 302 and 304. The female parent of the
304 cross was dead by the time the seed were mature and the
seed were discarded. The second and all subsequent generations
through 1930 were tested successively in infested soil in the
field and the results of the tests are shown in Table V.







Bull. 226, Development of Resistant Cigar Tobaccos 29

TABLE V. OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES FROM
CROSSES BETWEEN THE PARTIALLY RESISTANT BIG CUBA AND LITTLE CUBA
STRAINS OF TOBACCO WHEN GROWN IN THE FIELD IN INFESTED SOIL.

| Condition at End of Season
I No. of I_________
Generation I Progeny Number Plants Healthy Diseased
I Tested I Percent ILiving Dead
S Percent Percent
1925

Commercial Stock... Big Cuba (check) 200 1 3 96
Second...................... 301- 1 .................... 196 42 13 45
S301- 2 ........... .... 200 61 18 21
301- 4 ......... ...... 197 65 13 22
302- 1 .......... ..... 202 41 20 39
302- 2 ............ 190 37 12 51
302- 3 ..... .......... 196 48 17 35
302- 4 .................. 210 22 3 75
302-10 ................... 204 39 7 54
303- 3 ............. 188 30 19 51
303- 4 .............! 209 27 1 4 69
303- 6 .................... 195 1 42 18 40
303- 8 .................. 191 | 43 17 40
303-10 ................... 210 | 42 5 53
S303-11 ...............I.. 205 25 2 73
I I I


Commercial Stock..
Third......................


I Big Cuba (check)
S301-1-1 ................
301-2-1 .................
301-2-2 .................
301-4-1 .................
301-4-2 .................
301-4-4 .................
301-4-5 .............
302-1-1 ..............
302-1-2 .................
302-2-1 ..................
302-2-2 ................-
302-2-4 ..................
302-3-1 ..................
302-3-2 ...............-
302-3-3 .................

303- 3-1 ............
303- 4-1 ...............
303- 6-2 .............
303- 8-1 ...............
303- 8-2 ..............
303-10-1 ..............
303-10-3 ..............
303-10-5 .............







30 Florida Agricultural Experiment Station

TABLE V. OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES FROM
CROSSES BETWEEN THE PARTIALLY RESISTANT BIG CUBA AND LITTLE CUBA
STRAINS OF TOBACCO WHEN GROWN IN THE FIELD IN INFESTED SOIL.
-Continued.

S Condition at End of Season
No. of
Generation Progeny Number I Plants Healthy | Diseased
Tested Percent 1 Living Dead
I Percent Percent


Commercial Stock..

Fourth...---..........































Commercial Stock...

Fifth .............


1927

Conn. Round Tip I
(check) ........... 319
301-2-2-1 .......... 226
301-2-2-2 ........... 216
301-4-1-2 .............. 198
301-4-1-3 ............- 111
301-4-1-4 .....--..... 298

301-4-4-1 ............ 206
301-4-4-3 ............ 116
301-4-5-1 ............ 892
301-4-5-2 ............. 699
301-4-5-3 ..........3. 331
301-4-5-4 .......-.... 450

302-1-1-1 .......... 752
302-1-1-2 .......... 548
302-1-1-3 .... .... 272
302-1-1-4 ........... 560
302-1-1-5 ............ 554
302-1-1-6 ....-.......- 543
302-1-1-7 ............. 559

302-2-2-1 .............. 173
302-2-4-1 ............1 277
302-2-4-2 .............. 281
302-3-1-1 ............. 276
302-3-3-1 ............- 169

303-8-1-1 ...... ... 187
303-8-1-4 .............. 217
303-8-2-1 ............I. 134
303-8-2-5 .............. 166
303-10-3-1 .......... 75
303-10-3-5 ............ 158
1928


Conn. Round Tip
(check) .............
301-4-1-2-1 ...........
301-4-1-4-1 ............
301-4-1-4-2 ............

301-4-5-1-1 ............
301-4-5-1-3 ............
301-4-5-1-4 ............
301-4-5-1-5 ..........
301-4-5-1-7 ............
301-4-5-1-8 ............


0
74
72
60
90
70

81
86
85
85
80
75

75
76
76
68
83
78
66

64
66
58
67
83

79
79
78
75
96
93


858 0
37 76
73 85
46 89

434 92
134 85
82 97
121 92
135 93
89 92


1
2
5


100
17
11
26
7
19

15
5
6
9
14
16

18
17
11
25
11
12
26

16
20
20
26
14

14
13
12
21
0
7



100
19
15
2

7
13
2
7
5
3








Bull. 226, Development of Resistant Cigar Tobaccos 31

TABLE V. OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES FROM
CROSSES BETWEEN THE PARTIALLY RESISTANT BIG CUBA AND LITTLE CUBA
STRAINS OF TOBACCO WHEN GROWN IN THE FIELD IN INFESTED SOIL.
-Continued.


Progeny No.



301-4-5-1- 9 ..........
301-4-5-1-10 ..........
301-4-5-1-11 ..........
301-4-5-1-12 ..........
301-4-5-1-13 --.....

301-4-5-2-2 ............
301-4-5-2-3 ............
301-4-5-2-4 ............
301-4-5-3-1 ............
301-4-5-3-2 ............

301-4-5-3-3 ............
301-4-5-3-4 .........
301-4-5-3-6 .......
301-4-5-3-7 ............
301-4-5-3-8 .........

301-4-5-4-3 .........
301-4-5-10-2 ........
301-4-5-10-3 .....
302-1-1-6-1 ..........
302-1-1-6-2 ............
303-8-1-4-1 ............
303-10-3-1-1 ..........


No. of
Plants
Tested


261
342
338
273
203

204
209
147
97
89

128
250
118
244
317

210
254
143
47
60
44
85


I Condition at End of Season

Healthy I Diseased
IPercent /Living Dead
SPercent Percent


Commercial Stock...

Sixth.......................


Conn. Round Tip
(check) ............
301-4-5-1-1-1 .......
301-4-5-1-1-3 ........
301-4-5-1-1-4 ........
301-4-5-1-1-6 ........
301-4-5-1-4-1 ........

301-4-5-1-7-2 ........
301-4-5-1-7-3 ........
301-4-5-1-7-4 ........
301-4-5-1-8-2 ........
301-4-5-1-9-1 ..
301-4-5-1-9-3 ...-

301-4-5-1-10-4 ....
301-4-5-1-11-1
301-4-5-1-11-2
301-4-5-1-11-3 ..
301-4-5-1-11-4 ....

301-4-5-1-12-2 ..
301-4-5-1-13-1 ...


Generation







Florida Agricultural Experiment Station


TABLE V. OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES FROM
CROSSES BETWEEN THE PARTIALLY RESISTANT BIG CUBA AND LITTLE CUBA
STRAINS OF TOBACCO WHEN GROWN IN THE FIELD IN INFESTED SOIL.
-Continued.


I Condition at End of Season
] No. of _
Generation Progeny Number 1 Plants I Healthy Diseased
STested I Percent | Living Dead
I Percent Percent

301-4-5-1-13-3 ...... 63 98 0 2
301-4-5-1-S-1 ........ 255 97 1 2
301-4-5-1-S-2 ........ 135 1 98 1 1

S301-4-5-3-7-1 ........ 96 94 1 5
301-4-5-3-7-2 ....... 113 93 1 6
S301-4-5-3-7-3 ...... 268 94 3 3
301-4-5-3-7-4 -..... 71 93 4 3
301-4-5-10-3-1 .... 81 95 1 4
S301-4-5-10-3-2 ...... 28 82 7 11
1930


Commercial Stock.

Seventh..--..... -......


. Conn. Round Tip
(check) ............
. 301-4-5-1-S-1-1 ....
301-4-5-1-S-2-1 .
301-4-5-1-1-1-1 ....
301-4-5-1-1-1-3 ...

301-4-5-1-1-1-4 ..
301-4-5-1-1-6-1 ...
S301-4-5-1-7-2-1 ....
301-4-5-1-7-2-3 ..
301-4-5-1-7-2-4 -

301-4-5-1-7-2-6 ....
301-4-5-1-7-2-7 _
301-4-5-1-7-3-1 -.
301-4-5-1-10-3-1 -
301-4-5-1-10-3-2 -

301-4-5-1-11-2-1 .
301-4-5-1-11-2-4 .
301-4-5-1-11-3-2 .
301-4-5-1-11-3-3 j
301-4-5-1-11-3-4 --

S301-4-5-1-11-4-1 .
301-4-5-3-7-3-1

301-4-5-3-7-3-3 ....
301-4-5-3-7-3-4 ....
301-4-5-10-3-2-2 .-

303-10-3-1-1-1 ......
303-10-3-1-1-3 -.....-
303-10-3-1-1-4 ......
303-10-3-1-1-5 ......
303-10-3-1-1-6 ......






Bull. 226, Development of Resistant Cigar Tobaccos 33

As may be seen from Table V, the F2 progenies of the crosses
between partially resistant strains of Big Cuba and Little Cuba
showed relatively low resistance. However, with continued
selection and self-pollination through the F5, a highly resistant
strain was developed. Each year after 1926 certain selections
were dropped from the tests because of low resistance or un-
desirable leaf characters, or both. After 1928 all selections orig-
inating from the 302 cross were discontinued because of un-
desirable quality. The quality of the selections of 303 varied
with the season, being fair in certain seasons, and poor in other
seasons. The leaves of this strain are relatively broad in pro-
portion to the length and the lateral veins form a desirable angle
with the midrib. The average number of leaves per plant is
low but, on account of the large size of leaf, the yield would per-
haps be such that it could be grown profitably.
It will be observed that all strains of the 301 cross which have
been continued throughout the tests originated from the same
F3 individual. Certain selections of this strain have been elim-
inated because of undesirable leaf characters, low leaf number,
or lack of resistance, until the important characters of all selec-


Fig. 9.-Selections of the resistant strain 301 (left and right) and Con-
necticut Round Tip (center) in Phytophthora-infested soil in 1929.






Florida Agricultural Experiment Station


tions are more or less similar. Certain selections average one
or two more leaves per plant than others and there is usually a
slight difference in the shade of color of the green leaves. There
is also a slight difference in the angle which the leaves form with
the stalk. Furthermore, as may be observed in Table V, there
was still some difference in degree of resistance as between
selections in 1930.























Fig. 10.-The fifth (left) and tenth leaves from a plant of the resistant
strain 301. The angle formed by the lateral veins and midrib is about
the same as that of Little Cuba, the male parent.
Certain strains of 301 have been tested for two years on an
extensive commercial scale and in most cases the yield, quality,
and resistance in infested soil have been very satisfactory. Al-
though the weather conditions were not conducive to the produc-
tion of a good quality during the period of these tests, most
packers reported that the quality of 301 was as good as or better
than most crops of Connecticut Round Tip grown on new land.
Furthermore, the manufacturers have not discriminated against
it because it is a new strain of the cigar wrapper type. It suf-
fices to say, therefore, that 301 can be grown profitably in Phy-
tophthora-infested soil under Florida conditions.






Bull. 226, Development of Resistant Cigar Tobaccos 35

The quality of 301 has averaged very good for three years in
a series of fertilizer experiments on two acres of shade on the
Tobacco Station farm. Results of these tests will not be pre-
sented here, as they will be published after that experiment has
been concluded.
The seedlings of 301 reached the stage for transplanting sev-
eral days earlier than either of the parents or Connecticut Round
Tip. It matures in the field about seven to ten days later than
Little Cuba but is earlier than Big Cuba or Connecticut Round
Tip. There are certain minor objections to the 301 strain which
apparently may not be overcome by further selection. Chief
among these are the drooping habit of the leaves on the stalk
(Fig. 9) and a tendency for the leaves to turn or fold over on
the midrib during windstorms. The leaves are relatively large
(Fig. 10) and because of their tendency to droop it is difficult
to prime the lowest leaves without breaking the tips of some
of the ones immediately above. If the leaves turn on the mid-
rib their quality will be impaired unless they are turned back
to their natural position within 24 hours. This objection is over-
come largely by growing the crop under cloth or combination
shade with walls.
94
In 1926 a cross was made between selections of 301 and R and
assigned the number 94. In this cross the 301 plant was the male
parent and R the female. 'The parent plants were selected for
general vigor and desirable leaf characters. The reciprocal
cross was made using different individuals. The seed of this
cross were discarded because the root system of the female
parent was badly diseased when it was harvested. Ten other
crosses were made that year using selections of 301 in part of
them and other resistant strains in the remainder. The F2
progenies from the 11 crosses were tested in the field in infested
soil in 1927. Most of these F2 and subsequent progenies showed
a high degree of resistance to blackshank but only three of them
produced leaves of suitable quality for cigar wrappers. In this
respect the progenies of strain number 94 were outstanding and
only the results of tests with that strain will be considered in this
paper. Tests with selections of the other two strains will be
continued and reported upon later, if they should prove to be of
any commercial value. Results of the trials with the strain 94
from 1927 to 1930, inclusive, are shown in Table VI.







Florida Agricultural Experiment Station


It will be observed from Table VI that the F2, F3, and F. prog-
enies of 94 showed high resistance to blackshank. Although
several of the FS selections showed high resistance in 1930, many
of them showed more susceptible plants than any previous gen-
eration. This segregation into susceptible and resistant plants in
the F5 was more marked than was observed with any other strain
resulting from a cross.

TABLE VI.-OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES FROM A
CROSS BETWEEN RESISTANT 301 AND RESISTANT R TOBACCO PLANTS WHEN
GROWN IN THE FIELD IN INFESTED SOIL.


Generation




Commercial Stock. I

Second .....................


SCondition at End of Season
No. of I
Progeny Number Plants ) Healthy I Diseased
I Tested I Percent I Living Dead
SPercent Percent
1927

Conn. Round Tip |
(check) ..............I 286 0 2 98
94-1 .............. ....- 112 74 9 17
94-2 ----.................... I 74 73 16 11


1928

Commercial Stock. .l Conn. Round Tip
S (check) ............I 450 0 0 100
Third ........................ 94-1-1 ...................- 125 72 0 28
1 94-1-4 ............... ...| 373 91 2 7
S94-1-7 .................... 224 92 2 6
I 94-1-17 ................. 500 90 1 9
94-2-1 ................... 89 100 0 0
94-2-2 ...................- 174 99 0 1
S94-2-4 ....... ........ 108 87 2 11
94-2-5 ................... 367 88 4 8
S94-2-7 .................... 305 93 i 1 6


Commercial Stock... Conn. Round Tip
(check) ..--........
Fourth...................... 94-1-1-1 ....... .....-
S94-1-1-2 ..............
94-1-4-1 ............. I
94-1-7-1 ................
94-1-17-1 ---------

94-1-17-4 .............




S94-2-5-1 .-----
94-2-5-2 ................








Bull. 226, Development of Resistant Cigar Tobaccos 37

TABLE VI.-OCCURRENCE OF BLACKSHANK IN SELFED PROGENIES FROM A
CROSS BETWEEN RESISTANT 301 AND RESISTANT R TOBACCO PLANTS WHEN
GROWN IN THE FIELD IN INFESTED SOIL-Continued.


INo. of
Generation I Progeny Number Plants
STested


94-2-5-3
S94-2-5-5
S94-2-7-1
94-2-7-2

S94-2-7-4
94-2-7-5
S94-2-7-6
94-2-7-7
94-2-7-8


....... 72
... 63
......- 82
256

....... 257
....... 264
-...-. 124
....- 252
...... 259
1930


Commercial Stock.. Conn. Round Tip
(check) ............
Fifth..................... 94-1-1-2-1 ...........
S94-1-4-1-1 ..............
S94-1-17-1-1 ............

94-1-17-1-3 ...........
94-1-17-1-4 ..........
94-1-17-4-2 .........
94-1-17-4-3 .........
94-1-17-4-4 .........

94-2-1-1-1 ..........
94-2-1-1-2 ..............
S94-2-1-3-1 ...........
94-2-2-1-1 .........-
94-2-2-2-1 ..............

94-2-2-2-2 ............
94-2-5-2-1 ..............
94-2-5-2-2 ..............
94-2-5-2-3 ..............
94-2-5-2-4 ..............

94-2-5-3-1 .............
94-2-5-3-2 ..............
S94-2-5-3-3 ..............
94-2-5-5-1 ..............
S94-2-5-5-2 ..............

94-2-5-5-3 ............
S94-2-5-5-4 ..............
94-2-5-5-5 ..............
94-2-7-2-1 .............
S94-2-7-2-2 ..............


S94-2-7-2-3
S94-2-7-2-4


Condition at End of Season

Healthy Diseased
SPercent Living Dead
SPercent Percent

96 0 4
97 1 2
74 20 6
95 3 2

93 2 5
77 12 11
76 8 16
S 87 9 4
S 89 5 6


1 99
0 6
0 12
2 26

0 4
0 7
10 16
2 30
3 13

0 9
2 2
0 9
1 11
2 21

1 20
0 18
0 35
0 60
2 56

2 23
5 6
2 30
4 21
2 34

0 30
6 30
4 41
16 20
6 31

14 15
36 29


71 1
..............1 253 71
........-.....- 258 35 )







Florida Agricultural Experiment Station


TABLE VI.-OccuRRENCE OF BLACKSHANK IN SELFED PROGENIES FROM A
CROSS BETWEEN RESISTANT 301 AND RESISTANT R TOBACCO PLANTS WHEN
GROWN IN THE FIELD IN INFESTED SOIL-Continued.


Generation I Progeny Number


94-2-7-2-5 ..........
94-2-7-2-6 ...........
94-2-7-2-7 ............
94-2-7-2-8 .........
94-2-7-2-9 ............
94-2-7-2-10 ............
94-2-7-4-1 .............-
94-2-7-4-2 .............
94-2-7-4-3 ............
94-2-7-4-4 ..............
94-2-7-4-5 ..............
94-2-7-4-6 ..............
S94-2-7-4-8 ...........
94-2-7-4-9 .............
94-2-7-5-1 ..........---
94-2-7-5-2 ..............
94-2-7-5-3 .............

S94-2-7-7-1 .........
S94-2-7-7-3 .............
S94-2-7-8-1 ..............
S94-2-7-8-2 .............
I 94 (stock)* ...........


I
I
1
I


Condition at End of Season

Healthy I Diseased
Percent Living Dead
IPercent Percent


15


No. of
Plants
Tested


262
254
277
255
255
261
246
264

256
247
262
267
260
258
130
127
141

131
129
130
119
127


*This seed was a composite sample taken from a stock lot saved in 1929
from a commercial test by a grower.

There were noticeable differences in leaf characters among
plants of the F- selections and between sister selections in the F.
However, the selections 94-2-5 and 94-2-7 appeared very uniform
in all important morphological characters. The selection 94-2-7
possessed very desirable qualities for cigar wrapper, both in
size and shape of leaf and color and weight of the cured product.
Because of these desirable characters, a small acreage of this
selection was grown on a commercial basis in 1929. Results of
this trial, together with those of the test plots, aroused a great
deal of interest among the growers. The acreage of commercial
trials was increased in 1930 and as a whole the yield and quality
were satisfactory. In some cases the crop suffered severely
from drought and in such cases a higher percentage of black-
shank developed. The leaves of this strain possess characters
favored by cigar manufacturers.


26
32
12

29
33
11
19
12

15
12
26
14
17

12
18
35
23

21
12
15
4
19







Bull. 226, Development of Resistant Cigar Tobaccos


Fig. 11.-The fifth (left) and tenth leaves from a plant of the resistant
strain 94. The angle formed by the lateral veins and midrib is about
the same as that of Connecticut Round Tip.


Fig. 12.-Two selections of the resistant strain 94 in Phytophthora-in-
fested soil in 1929. Photographed after about one-third of the leaves
had been harvested.






Florida Agricultural Experiment Station


The lateral veins of the 94 strain form an angle with the mid-
rib (Fig. 11), which is desirable for successful stripping by ma-
chinery. Other characters of the cured leaf which constitute
quality, as firmness, elasticity, and fineness of texture, are con-
sidered excellent. Also, the yield and characters of growth in
the field have been satisfactory. The strain has not been tested
long enough to be sure that the type is fixed in any of the selec-
tions, but it seems to possess the most desirable characters for
cigar wrappers of any new strain. The seedlings reach the stage
for transplanting and mature in the field several days earlier
than the Big Cuba or Connecticut Round Tip. Growth charac-
ters of two of the sister strains growing in infested soil in 1929
are shown in Fig. 12.
OTHER CROSSES
During the last four years 36 other crosses have been made.
Most of these were between resistant strains which possessed
certain qualities desired in cigar wrappers. Although the prog-
enies of several of the crosses show indications of desirable com-
binations for the improvement in quality of leaf and resistance
to blackshank, the trials have not been continued long enough
to warrant a detailed report here.
DISCUSSION

The evidence obtained in connection with these studies leads
to the conclusion that of the numerous commercial varieties of
tobacco tested only a few show any resistance to the attack of
Phytophthora nicotianae Breda de Haan. Only a very small
percent of the plants of most of these few varieties resist the
parasite under favorable conditions for development of the dis-
ease. Such plants were usually heterozygous for resistance and
their progenies showed no uniformity in the segregation of re-
sistant and susceptible individuals. The first generation of some
of the plants showed high resistance, while others showed vari-
ous degrees of resistance. Highly resistant strains were isolated
by continuing to select the most resistant plants for several years
but the increase in degree of resistance from year to year was
gradual in most cases. Strains completely free of susceptible
plants under field conditions in the Florida-Georgia district have
not been obtained.
The commercial varieties known as Dubek (Russia) and Ha-
vanensis (a Cuban wrapper type) were the exceptions in that






Bull. 226, Development of Resistant Cigar Tobaccos 41

they showed a high degree of resistance to blackshank. How-
ever, continued selection of the resistant plants has not resulted
in completely resistant strains of these varieties when grown
under field conditions.
The information obtained does not explain satisfactorily the
failure to obtain strains of tobacco completely free from sus-
ceptible plants. It also fails to explain why so many years select-
ing and selling were required to isolate highly resistant strains
from certain varieties and crosses. However, the results indicate
that the resistant character is not governed by a simple genetic
factor and that resistance is a relative condition, since it is
affected by the environment. Assuming that the initial selected
plants were heterozygous for the resistant character, it should
be possible by selecting and selling the best plants to eliminate
the undesirable susceptible character in the second or third
generation. This should be expected particularly with diseases
such as blackshank of tobacco in which the causal parasite sur-
vives in the soil from year to year under environmental con-
ditions which are favorable for development of the disease dur-
ing a greater part of the growing season. It appears rather im-
probable that the plants selected for seed in the trial plots had
escaped contact with the parasite, since the susceptible varieties
used in the check rows almost invariably showed 100 percent in-
fection. Since, during the last three years, certain selections
were made in an effort to maintain particular leaf characters, it
is possible that in such cases the plants were selected each year
from the group which was heterozygous for the resistant char-
acter. However, during the first three years of the work plants
were selected from the Big Cuba variety for resistance regard-
less of leaf characters. Even so, five years were required to
develop a highly resistant strain of that variety.
Data obtained over a period of three years have indicated that
injury caused by the root-knot nema (Heterodera radicicola
(Greef) Mueller) may affect the degree of resistance. In several
instances the trial plot in commercial fields proved to be heavily
infested with this nema. In all such cases the same strains of
tobacco showed a lower degree of resistance than in fields with
slight nema infestation. The plants which succumbed to black-
shank late in the season usually showed severe nema injury,
while the ones which remained free from blackshank in the
same field usually showed slight injury from this cause.
Cultural methods also appear to affect resistance. In all the







Florida Agricultural Experiment Station


trials in commercial fields the plants were grown under cul-
tural practices followed by the farmer. In several instances the
farmer cultivated deep until late in the season. Under such
conditions the resistant strains showed less resistance to black-
shank than in fields where shallow cultivation was used. This
was especially noticeable in years when there was light rain-
fall during the growing season. Such cultural methods ma-
terially retard the growth of the crop, even on uninfested soil,
and it appears probable that an injurious effect would also be
exerted on the resistant character.
High temperature also may affect the degree of resistance.
The optimal temperature for growth of Phytophthora nicotianae
in culture is from 250 to 300C., but the optimal temperature for
the growth of cigar wrapper tobacco has not been determined.
The temperature under the shades reaches a maximum of 350-
400C. for several hours of the day during the latter part of
the season. Oftentimes this high temperature is accompanied
by light rainfall. Under such conditions the growth of tobacco
plants was greatly checked. Thus, it appears probable that the
high temperatures which obtain under field conditions at cer-
tain periods of the year may weaken the resistant character.
It is planned to study in the future the effect of these environ-
mental factors on the resistant character.
No evidence has been accumulated in these investigations
which shows that resistance to blackshank is linked with im-
portant type characters of tobacco or with resistance to other
diseases. Resistant strains have been obtained from several com-
mercial varieties which represent as many leaf types. Further-
more, among the numerous varieties tested for resistance to
blackshank, Connecticut Round Tip, Halladay Havana, and Xan-
thia (Turkish) have been reported to be resistant to Thielavia
root rot." All of these varieties proved 100 percent susceptible
to blackshank. Furthermore, a strain of Big Cuba resistant to
root rot which was developed in Florida was completely suscep-
tible to blackshank.
The resistant strain of Big Cuba differs from the commercial
variety in having a slightly darker green color of leaves with
undulate or ruffled margins. The apparent reason for these
deviations is that the disease reduced the plants available for
the original selections to a very small group and there was little
"Johnson, James. Breeding tobacco for resistance to Thielavia root
rot. U.S.D.A. Tech. Bul. 175:1-20. 1930.







Bull. 226, Development of Resistant Cigar Tobaccos 43

opportunity to select for the predominant type of the commercial
variety. The quality of the cured leaf of this resistant strain
and of the commercial variety is about the same when the plants
are grown under similar conditions.
Yield and "demands of the trade" are the principal factors
to be considered in connection with the introduction into com-
merce of these resistant strains. On account of the high cost of
producing tobacco under artificial shade in Florida and of the
fluctuation in price of the cured leaf from year to year, with a
rather definite upper limit, it has been estimated that a variety
which yields less than 1,000 pounds per acre is unprofitable.
Therefore, since Phytophthora nicotianae has become so gen-
erally distributed in the Florida-Georgia district, it is impracti-
cal to attempt to grow the standard susceptible variety, except
on a limited scale in certain localities. During 1929 and 1930
the blackshank resistant strains 301 and 94 were substituted in
an increasing percentage for the susceptible Connecticut Round
Tip and they produced a profitable yield on infested soil.
The demand for light colored, thin, mild, and free-burning
tobacco comes clearly from the manufacturer and consumer who
have used large quantities of Florida-grown wrappers for years.
Consequently, it would be quite unprofitable to grow a large
yield of any quality of leaf which does not meet these demands,
as both of these factors determine whether the crop can be grown
at a profit. Fortunately, the new strains 301 and 94 have been
accepted favorably by the trade and since the yield was satis-
factory the growers were enabled to continue operations. With
a few more years' experience in growing and packing these
strains, it appears probable that a higher yield per acre of the
best grades will be produced on infested soil than was formerly
obtained with the standard susceptible varieties before black-
shank occurred in the district.

SUMMARY
The nature of the disease, and the method of hybridization and
testing progenies of tobacco in the field for resistance to black-
shank, are described.
The P strain is a resistant selection from Big Cuba, a com-
mercial variety of cigar wrapper tobacco which was grown under
shade almost exclusively from 1909 to 1922. After selecting and
selfing for six years, a strain was obtained which showed a high






Florida Agricultural Experiment Station


degree of resistance to blackshank in thoroughly infested soil.
This resistant strain resembles the parent variety in its main
features and quality of leaf, although under certain conditions
the cured leaf is slightly more sleazy.
In like manner resistant strains have been developed from the
Little Cuba (Cuba), Dubek (Russia), and Santiago (Java)
varieties.
The quality of Little Cuba is considered very good but it cannot
be grown profitably under shade in Florida because of the low
yield. Dubek and Santiago are not cigar wrapper varieties and
the yield is low. The resistant strains of these three varieties
closely resemble the parent varieties in all the main characters
that were compared.
Number 1 is a new resistant strain resulting from a cross
between a partially resistant strain of Big Cuba and susceptible
Connecticut Round Tip. After selecting and selling for six gen-
erations from the cross, progenies were obtained which showed
a high degree of resistance under conditions favorable for de-
velopment of the disease. The leaves of this strain are larger
than those of either parent but in the main characters they re-
semble Big Cuba more than Connecticut Round Tip. The main
characters appear to be fixed, although the strain is not com-
pletely resistant when grown in the field. The color of the cured
leaf is good, but it is fairly coarse and has a bitter taste.
R is a new resistant strain resulting from a suspected cross
between a resistant strain of Big Cuba and susceptible Connecti-
cut Round Tip. After selecting and selfing for five generations,
progenies were obtained which showed great uniformity in
growth characters and were highly resistant to blackshank. The
shape, size, and quality of leaf are similar in the main features
to Connecticut Round Tip. This variety has not been tested ex-
tensively under slat shade but it appears to have possibilities
for a good wrapper tobacco.
Number 301 is a new strain resulting from a cross between
resistant Big Cuba and resistant Little Cuba. After selecting
and selfing for six generations, progenies were obtained which
were uniform for the important growth characters and resist-
ance to blackshank. The leaf characters represent a blend of
those of both parents. The maturity is intermediate. The seed-
lings reach the stage for transplanting from seven to ten days
earlier than Big Cuba and Connecticut Round Tip. This strain
has been tested two years on an extensive commercial scale and






Bull. 226, Development of Resistant Cigar Tobaccos 45

in most cases the quality proved to be very good. Undesirable
characters of this strain are manifest in the drooping position
of the leaves on the stalk and turning of the leaves on the midrib.
Number 94 is a new strain resulting from a cross between 301
and R. After selecting and selfing for four generations, prog-
enies were obtained which showed uniformly high resistance
to blackshank in thoroughly infested soil. Tests have not been
continued a sufficient number of years to be sure the type is
fixed, although some of the selections appear uniform for leaf
characters. The shape and size of the leaf of this strain are
somewhat similar to Connecticut Round Tip and the yield will
probably be as great under most conditions. It is about the
same as 301 in earliness of seedlings and maturity of leaf. So
far, the quality of cured leaf has been superior to that of any
other variety tested. Further selections are being made from
the best progenies and they will be multiplied for trial on a com-
mercial scale as soon as the trials justify releasing them.
Three of the resistant strains have been released for com-
mercial growing. These are P, 301, and 94. However, there is
little demand for the P strain because of certain undesirable
morphological characters and inferior quality. The quality of
both 301 and 94 is very good but 94 has fewer objectionable
growth characters.




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