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represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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Copyright 2005, Board of Trustees, University
?5^- ; ....... "" *- -"*-;
O ) Progress in Breeding for Combined Resistance ,- .
to Diseases in Tomatoes
R. B. Volin-
I. Introduction and objectives.
Disease organisms which infect the plant and fruit of tomato cause considerable
loss in yield and fruit quality. Producers must apply expensive chemicals ifoOr:
control which often are less than effective. Chemical applications are-also.--.
becoming closely regulated by control agencies and less and less popular with
the consuming public. The objectives of this project are to select and assemble
disease resistant breeding stocks for use in the Florida tomato breeding program
and to gain knowledge pertaining to the genetics of disease resistance.
II. Resistance to Verticillium wilt was located in an early tomato accession named
'Peru Wild' and reportedly was conditioned by a single dominant factor referred
to as the "Ve" gene (2,3). Numerous varieties with the Ve gene have been devel-
oped including the early 'Loran Blood', 'VR Moscow', 'H 1350', 'Porte' and
several "VF" stocks from California. Since their release researchers have re-
ported isolates of V. albo-atrum which are pathogenic on stocks carrying the Ve
gene (1,4). Current research suggests that resistance is polygenic and
An arduous screening program for resistance has been under way for some time
at the AREC in Homestead. The results of infecting tomato seedlings of a num-
ber of breeding lines and cultivars with Verticillium albo-atrum inoculum are
shown in Figure 1. The averages are from data collected over a period of from
two to seven seasons. Since none of the screening was done under controlled
environment, fluctuating weather conditions contributed to the wide variability
within varieties. Pathogen isolates were variable in composition and concen-
tration. Another factor which may contribute to the high variability is an
uncertain number of quantitative genes conditioning resistance within a given
Research is currently under way to determine the genetics of Verticillium re-
sistance in Florida tomato breeding lines. Stocks exhibiting a high degree of
susceptibility have been combined with those highly resistant. A study and
analysis of the progeny, under controlled environmental conditions, will lend
information about the inheritance of resistance.
A preliminary effort was made to determine if pathogen isolates differ in viru-
lence. Testing was done under greenhouse conditions. Four tomato cultivars
were used as differential varieties. Roots of week-old seedlings were dipped
in a mycelium-conidial suspension of each isolate containing ca. 106 conidia
per ml. Response was recorded 2 weeks after transplanting in the greenhouse.
The results did not clearly indicate the presence of different strains :or
virulence factors within the pathogen (Table 1). The Homestead isolate was,
however, less pathogenic on all varieties. Another comparison should be made
utilizing a growth chamber, additional host cultivars and replicated treatments.
1/ Assistant Plant Pathologist, University of Florida, IFAS, Agricultural Research
and Education Center, Homestead, Fla. 33030.
SIII. Resistance to grey leafspot.
Resistance to grey leafspot, caused by Stemphyllium solani, has been present
in all the Florida varieties since Manalucie was released in 1953. A high
degree of resistance is demonstrated as well as history of stability against
The genetics of resistance in tomato to S. solani is not well understood. It
has been reported by some to be conditioned by one dominant gene yet others
have reported the inheritance more complex (4).
A group of crosses have been selected to be used in a study of the inheritance
of resistance. It is hoped this study will provide knowledge basic to the
continued incorporation of resistance in Florida breeding stocks.
IV. Resistance to the "old land" complex.
Studies on the pathogen causing tomato decline on land after successive cropping
are continuing. Field evaluation coordinated with controlled temperature
studies in the greenhouse indicate a number of tomato types may be resistant or
in some cases tolerant to the malady (Table 2). Some of the most promising
fresh market breeding lines and established cultivars have been crossed with
these types. Since the resistant types all produce very small fruit, recovery
of acceptable fruit traits in progeny may be slow and laborious requiring numer-
ous backcrosses. It may be possible however to locate sources of resistance to
other diseases in these studies.
* V. Additional areas of importance.
A lengthy description of additional areas of research would be unnecessary and
quite preliminary. This is because work was recently initiated or it receives
less than primary consideration. A brief listing includes the following:
1. Nature of and incorporation of resistance to early blight, Alternaria
2. Nature of and .incorporation of resistance to bacteria spot, Xanthomonas
3. Study of the prevalence of and assay resistance to target leaf spot,
4. Obtain tomato stocks with resistance or tolerance to Potato Virus Y.
VI. Literature Cited
1. Alexander, L. J. 1962. Susceptibility of certain Verticillium resistant
tomato varieties to an Ohio isolate of the pathogen. Phytopathology 52:
2. Doolittle, S. P. 1954. The use of wild Lycopersicon species for tomato
disease control. Phytopathology 44:409-414.
3. Schaible, L. O., 0. S. Cannon and V. Waddoups. 1951. Inheritance of
resistance to Verticillium wilt in a tomato cross. Phytopathology 41:
4. Walter, J. M. 1967. Hereditary resistance to disease in tomato. Ann.
Rev. Phytopathol. 5:131-162.
Table 1. Response of tomato cultivars
to isolates of Verticillium
Isolate % plants showing wilt symptoms-/
source VR Moscow Tropic Red Top Walter Average
Ohio2/ 7.9 17.5 92.1 100.0 54.3
Okra 7.9 11.1 96.8 96.8 53.2
Walter2/ 6.4 7.9 92.1 93.6 50.0
SC 6592- 6.4 6.4 90.5 92.1 48.8
Avocado 7.9 12.7 87.3 85.7 48.4
Homestead 242/ 1.6 1.6 47.6 66.7 29.4
Control 0 0 0 0 0
Average 6.3 9.5 84.4 89.2
SResponse was recorded
2 weeks after week-old seedlings were
2/ Culture isolated from tomato.
Table 2. Tomato accessions resistant or tolerant to the "old land"
P.T~ Niimbnr andl orivin
263,719 Puerto Rico
P.T.. lumber and origin
272,813 El Salvador
272,840 El Salvador
272,870 El Salvador
Lycopersicon f. pyriforme
L. esculentum x L. hirsutum
L. esculentum x L. pimpinellifolium
L. peruvianum var. humifusum
Evaluations were made by Dr. R. T. McMillan, Jr., Associate Prof.
of Plant Pathology, and Mr. Jorge Parrado, Laboratory Technician
P I Number and oric-,~-in P.I Number and origin--
a ,' *
Fig. 1. Average percent resistance of seedling tomato cultivars or breeding
lines to Verticillium over two to seven seasons. The range in per-
centage for each selection is given as a single horizontal line.
PERCENT OF PLANTS RESISTANT
-- ._ i