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United States Department of Agriculture

Agricultural Research Service

2008 Annual Report

1a.Objectives (from AD-416)
The overall objective of this project is to develop novel basic and applied solutions within an integrated/organic framework for reducing disease and insect losses in cucurbit crops while producing safe, nutritious products for consumers. The specific objectives include: .
1)identify and develop systems for suppression of soilborne diseases using grafting and/or biofumigant crops to formulate novel control strategies applicable to organic and conventional vegetable speciality crops; .
2)elucidate virulence parameters of selected pre- and postharvest pathogen populations, define the role of polygalacturonase-inhibiting protein (PGIP) as a plant pathogen defense mechanism, and use this information to develop integrated methodologies for natural control of cucurbit diseases in conventional and organic production; .
3)characterize strains of Serratia marcescens from different ecological niches with special reference to the phloem-inhabiting strain that causes cucurbit yellow vine disease; .
4)develop behavior-based alternative controls for insect vectors of CYVD and other key insect pests of vegetable crops; and.
5)identify and develop disease-resistant germplasm and inbred lines for release to the seed industry.

1b.Approach (from AD-416)
Because plant-pest/host relationships are inherently difficult to study, more precise methods of quantifying pathogen virulence and of understanding insect behavior are prerequisite in formulating and measuring effective pest control strategies. This project's overall approach is to develop technologies necessary to devise integrated systems for conventional and organic producers to control disease and insect pests of watermelon, cantaloupe, and other specialty crops. Biofumigant crops (mustard) and biocontrol microbes will be integrated into the cropping system along with resistant germplasm for suppression of soilborne diseases. Grafting plants onto resistant rootstock will be part of a diverse approach for developing sustainable farming systems.

3.Progress Report
As an alternative to methyl bromide fumigation, Indian mustard was planted in field plots alone and in combination with: a) chicken litter organic matter, b) mustard meal, c) humic acid/humates, and d) multi-component microbials, for the control of Fusarium wilt in watermelon. (NP303, Component 4, Problem Statement 4A, 4B, and 4C) Watermelon was grafted onto gourd rootstock to evaluate Fusariumm wilt control and fruit quality. (NP303, Component 4, Problem Statement 4A and 4C) Isolates of Fusarium oxysporum were tested in greenhouse studies to establish virulence parameters and race identification of strains. Laboratory experiments were undertaken to develop bioassay system for identifying toxins produced by F. oxysporum f. sp. niveum. (NP303, Component 2, Problem Statement 2A) Laboratory experiments were undertaken to separate the functional form of cantaloupe PGIP expressed predominantly in mature fruit from the functional form expressed in immature fruit. (NP303, Component 2, Problem Statement 4B) Laboratory experiments were undertaken to develop and to establish criteria for strain identification in 50 isolates of the Cucurbit Yellow Vine Disease (CYVD) strain of Serratia marcescens using fatty acid methyl esters. (NP303, Component 2, Problem Statement 2A) Biolog analysis was initiated for additional characterization of CYVD strains and to evaluate its potential for strain identification. (NP303, Component 2, Problem Statement 2A) Citrullus colocynthus X C. lanatus crosses were made to determine if resistance to CYVD is physiological or due to altered insect feeding preference. (NP303, Component 2, Problem Statement 2A) Squash bugs (male, female, or both) were placed in traps near watermelon and squash to determine if there was differential attraction in squash bugs based on sex. Various types of plastic mulches were utilized to determine the effects on squash bug feeding behavior and incidence of CYVD. Insect populations were quantified in the plastic mulch studies. Kaolin was evaluated to determine the effect on squash bug feeding behavior. (NP303, Component 2 and 4, Problem Statement 2A and 4B) Genetic resistance to race 2 powdery mildew was found in watermelon and resistant lines will soon be released. Recombinant inbred lines with differential expression for resistance to powdery mildew race 1 and 2 are being developed. (NP 303, Component 5A, Problem Statement 3B)

1. Bioassay for Fusarium oxysprorum toxins developed: Improved knowledge of the biological mechanism by which Fusarium oxysporum f. sp. nevium causes wilt in watermelon will allow design of more direct and "greener" approaches to combat this disease. One approach to understanding the disease is to know the chemical nature of the toxins secreted by the fungus once it invades the plant through the plant roots. Scientists at the South Central Research Laboratory in Lane, OK, have developed a bioassay for Fusarium toxins using watermelon seedlings. By employing this bioassay together with separation techniques, the fungal-secreted compounds that are toxic to the plant can be enumerated. Knowledge of the chemical structure of these compounds may then be utilized to develop treatments for Fusarium wilt in watermelon. (NP 303, Component 2, Problem Statement 2A)

2. Grafting watermelon onto gourd rootstock: The study was designed to determine the effects that grafting watermelon onto gourd or squash rootstocks has on fruit firmness, lycopene content, and total soluble solids (TSS). Scientists at the South Central Research Laboratory in Lane, OK, determined that watermelon fruit, using Cucurbita ficifolia or Cucurbita maxima x Cucurbita moschata hybrid as the rootstock, consistently had higher fruit firmness values. In these studies, grafted watermelon did not enhance nor reduce lycopene content or TSS. The different rootstocks used in these studies demonstrated a high tolerance to both Verticillium dalhiae and Fusarium oxysporum f. sp. nevium. However, there was limited colonization by both pathogens. Grafting holds promise as a mechanism to control many soilborne diseases and improve fruit quality in watermelon. (NP 303, Component 4, Problem Statement 4A)

3. Powdery Mildew resistant watermelon developed. Powdery Mildew on watermelon, which appeared in the U.S. in early 2000, can have an economic impact for many watermelon growers and seed companies. Recombinant inbred lines with differential expression for resistance are being development by a scientist at the South Central Agricultural Research Laboratory, Lane, OK. Genetic resistance to race 2 Powdery Mildew were found in watermelon; resistant lines will soon be released. The recombinant inbred line will be used to map resistance genes and the development of molecular markers for resistance screening. Incorporating this resistance into improved commercial cultivars will help control spread of this disease. (NP 303, Component 5A, Problem Statement 3B)

5.Significant Activities that Support Special Target Populations
Provided disease identification techniques, monitoring of disease development, and supplied pest management strategies for African-American and Hispanic farmers.

Mentored a Native American student during the summer Choctaw Nation work program.

6.Technology Transfer

Number of Non-Peer Reviewed Presentations and Proceedings4
Number of Newspaper Articles and Other Presentations for Non-Science Audiences2

Review Publications
Bruton, B.D., Fish, W.W., Langston, D.B. 2008. First report of Fusarium wilt caused by Fusarium oxysporum f. sp. niveum Race 2 in Georgia watermelon. Plant Disease. 92(6):983.

Davis, A.R., Levi, A., Tetteh, A., Wehner, T., Russo, V.M., Pitrat, M. 2007. Evaluation of watermelon and related species for resistance to race 1W powdery mildew resistance. Journal American Society Hortscience. 132(6):790-795.

Taylor, M.J., Bruton, B.D., Fish, W.W., Roberts, W. 2008. Cost benefit analyses of using grafted watermelon transplants for Fusarium wilt disease control. Acta Horticulturae. 782:343-350.

Last Modified: 9/10/2014
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