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United States Department of Agriculture

Agricultural Research Service

2009 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 control of Fusarium wilt in watermelon. Plant populations ranged from 75,000 to 175,000 plants/acre. Excessive spring rains greatly delayed incorporation of plant biomass at the appropriate time, resulting in unsatisfactory results. Five rootstocks composed of gourd and squash were tested to determine resistance to two wilt-inducing pathogens of watermelon. Each of the rootstocks was found to be highly resistant to the Fusarium wilt (race.
2)and Verticillium wilt pathogens in greenhouse trials. Although each of the rootstocks was determined to be highly resistant to both pathogens, there was limited colonization of the root and crown of the rootstocks with no adverse effects. The activity levels of ten cell wall degrading enzymes (CWDE) were measured in Bacillus sp. lesions in honeydew melon fruit. Xylanase, pectin methylesterase, and beta mannanase were the only enzymes whose activities were elevated in the lesion. The activities of enzymes that destroy structural integrity such as polygalacturonase, pectin lyase, and cellulase, were low and exhibited no difference between healthy tissue and the lesion. These observations are consistent with the physical appearance and behavior of the lesions. A manuscript is in preparation. The physical properties of the mature form of CmPGIP are identical to those of the immature form. It is likely that the difference in binding affinities of the two forms to fungal polygalacturonase is the result of a small number of amino acid substitutions at or near the binding site on the CmPGIP. Attempts to purify sufficient quantities of the mature form of CmPGIP to prove this are underway. Approximately 100 Serratia marcescens isolates were characterized by Fatty Acid Methyl Ester (FAME) analysis to evaluate the sensitivity of FAME for identifying isolates that cause the Cucurbit Yellow Vine Disease (CYVD) and those isolates from other niches that do not cause CYVD. Statistical analysis of the data is underway. Genetic resistance to race 2W powdery mildew was found in watermelon and resistant lines are being released. Recombinant inbred lines with differential expression for resistance to powdery mildew race 1W and race 2W are almost fully developed. Genetic studies of inheritance of race 1W and race 2W powdery mildew resistance is nearly completed and manuscripts are in preparation.

1. 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. Genetic resistance to race 1W and race 2W Powdery Mildew was found in watermelon. Inheritance of these genes was elucidated and manuscripts are in preparation or have been submitted to report this data. Incorporating this resistance into improved commercial cultivars will help control this disease without pesticide use and will slow the spread of this disease.

2. Some dsRNAs decrease reproductive potential in Monosporascus cannonballus: Thousands of acres of melons are grown in southern parts of Texas, Arizona, and California on land that is infested with the fungus known as Monosporascus cannonballus. The population of this fungus can increase following multiple crops of melons on the same land and severely limit production. A research consortium consisting of scientists at the University of Valencia, Spain; East Central State University, Oklahoma; and the South Central Agricultural Research Laboratory in Lane, Oklahoma, demonstrated that the mere presence of dsRNA in M. cannonballus is not involved in degeneration of the fungus. However, the presence of certain dsRNAs appears to be associated with reduced ability for fungal reproduction. The potential impact of this research is enhanced plant resistance to the fungus, reduced spore production, and therefore reduced disease potential of the pathogen using RNAi technology.

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

6.Technology Transfer

Number of Web Sites Managed1

Review Publications
Cluck, T.W., Biles, C.L., Dugan, M., Jackson, T., Carson, K., Armengol, J., Garcia-Jimenez, J., Bruton, B.D. 2009. Association of dsRNA to down-regulation of perithecial synthesis in Monosporascus cannonballus. Open Mycology Journal. 3:9-19.

Bruton, B.D., Fish, W.W., Roberts, W., Popham, T.W. 2009. The influence of rootstock selection on fruit quality attributes of watermelon. Open Food Science Journal. 3:15-34.

Last Modified: 9/21/2014
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