Gulf Coast Research and Education Center
14625 C.R. 672, Wimauma, FL  33598
(813) 634-0000  SC514-6890
Fax (813) 634-0001
 Jack Rechcigl, Center Director

Diseases of Vegetable Crops

The disease forecasting systems Blightcast and Downcast accurately predict the occurrence of late blight in tomato and downy mildew in cucurbits, respectively, in southwest Florida.  Effective control measures were developed for Fusarium wilt and Fusarium crown rot (F. oxysporum f. sp. lycopersici) of tomato based on preplant soil fumigation and manipulation of host and pathogen nutrition.  New pathogenic races of Fusarium wilt and Verticillium wilt (Verticillium albo-atrum) were discovered and control strategies developed.  In the 1990s, Phytophthora blight (Phytophthora capsici ) was identified as a major pathogen of most important cucurbit and solanaceous crops across the state.  Recent research has focused on characterizing the survival, dissemination, and fungicide resistance of P. capsici, and development an integrated approach to its management.
 
The disease forecasting systems Blightcast and Downcast accurately predict the occurrence of late blight in tomato and downy mildew in cucurbits, respectively, in southwest Florida. Effective control measures were developed for Fusarium wilt and Fusarium crown rot (F. oxysporum f. sp. lycopersici) of tomato based on preplant soil fumigation and manipulation of host and pathogen nutrition. New pathogenic races of Fusarium wilt and Verticillium wilt (Verticillium albo-atrum) were discovered and control strategies developed. In the 1990s Phytophthora capsici (Phytophthora blight) was identified as a major pathogen of most important cucurbit and solanaceous crops across the state. Recent research has focused on characterizing the survival, dissemination, and fungicide resistance of P. capsici, and developing an integrated approach to its management.
 
Bacteria. Significant progress was made on understanding the etiology and management of bacterial spot (Xanthomonas campestris pv. vesicatoria) and bacterial speck (Pseudomonas syringae pv. tomato) of tomato and bacterial spot of pepper (X. campestris pv. vesicatoria). Ecological studies of Xanthomonas were made possible by the development of selective media and other laboratory techniques that permitted monitoring indigenous populations of the pathogen. New races of Xanthomonas including copper-resistant strains were identified and control measures established. Nutritional and chemical studies including identifying the advantageous combination of dithiocarbamate fungicides and copper have lead to more effective control of both bacterial spot and bacterial speck.
 
In the 1980’s several sources of resistance to bacterial spot of tomato were identified, which have been used in the tomato breeding program in Florida and in commercial breeding programs throughout the world. This resistance was associated with a hypersensitive response and was the first known source of this type of resistance in tomato. Several other bacterial diseases were identified in the 1980s. Tomato pith necrosis was first identified in Florida and California in the same year. Another bacterial disease which resulted in foliar blighting of tomato and pepper during the cool, wet spring was identified as being caused by Pseudomonas viridiflava. More recently in the late 1990s, a novel strategy was initiated to use bacteriophages (virus particles that infect and destroy bacterial cells) specific to X. campestris pv. vesicatoria to control the bacterial spot disease of tomato. Considerable success has occurred and vegetable transplant houses are currently using this strategy to control bacterial spot.
 
Viruses. A virology research program was established at GCREC in 1991 in response to the presence of a new whitefly-transmitted geminivirus, tomato mottle virus, which caused significant yield losses in the tomato industry. The primary focus of this program has been the identification, characterization, and management of whitefly-transmitted geminiviruses. Rapid and sensitive reagents for detection of tomato mottle virus were developed, and studies were conducted to determine the host range and to characterize the epidemiology of the virus. Trials evaluating insecticides for vector management were conducted to identify those that can be used to manage virus incidence. The results of these studies were used to develop successful management recommendations for tomato mottle virus. This virus is no longer a problem in Florida.
 
A newly introduced exotic whitefly-transmitted geminivirus, tomato yellow leaf curl virus, was identified in Florida in 1997. This virus causes yield losses in tomato and can infect other crops as well. Studies were conducted to identify the host range and to understand the means by which the virus spreads. Preliminary recommendations for its management were made immediately following the identification of the virus, with improved recommendations being made as studies were completed.

Studies were conducted on whitefly-transmitted geminiviruses in the Caribbean area to give Florida growers advance warning of possible virus introductions. Viruses identified for the first time are potato yellow mosaic virus in tomato in Guadeloupe and Martinique, tomato yellow leaf curl virus in tomato in the Dominican Republic and Jamaica, and several unnamed viruses from Guadeloupe and the Dominican Republic. In 1993, this program cooperated in the identification of bean golden mosaic virus, a new whitefly-transmitted geminivirus of bean in south Florida. This virus is a major limiting factor in bean production throughout the American tropics and subtropics. New sources of resistance to bean golden mosaic virus have been identified, e.g. Phaseolus acutifolius provides immunity in fresh market bean.
 
In addition to the development of integrated practices for management of these viruses, major emphasis has been placed on the development of resistant varieties through the use of genetic engineering. Tomato breeding lines were transformed with mutated genes from tomato mottle virus that were designed to interfere with virus replication and prevent systemic infection. Highly resistant tomato mottle virus and high-yielding breeding lines were developed.
 
However, the appearance of the highly virulent tomato yellow leaf curl virus has precluded their release, and research efforts have shifted to the development of lines with resistance to both tomato mottle and tomato yellow leaf curl viruses. Recently resistance to tomato yellow leaf curl has been developed and research is underway to combine the two resistances into highly resistant, high yielding varieties for Florida production.