1a. Objectives (from AD-416)
The objective of this project is to develop novel, biologically-based disease-control strategies for temperate fruit crops in order to reduce the use of chemical pesticides. This will be done by identifying microbial antagonists that are effective against latent and wound-induced infections of stone fruit, determining the genetic factors that make the brown rot pathogen so virulent by comparing host response to pathogenic and non-pathogenic organisms, and determining the role of fungal polygalacturonases as a virulence factor for postharvest infections of pear and peach.
1b. Approach (from AD-416)
The project will utilize a broad range of approaches to develop new biologically-based methods of postharvest disease control. Naturally-occurring yeasts and bacteria will be isolated from stone fruit and screened for activity against latent and wound-induced infections of stone fruit caused by the brown-rot organism, Monolinia fructicola. As part of the evaluation, select microbes will be tested for their ability to degrade melanized fungal structures such as appressoria using a model membrane system. Subtractive-suppressive hybridization of cDNA libraries will also be utilized to better understand the genetic basis of resistance mechanisms in stone fruit. This will be done by comparing host response at different developmental stages to both pathogens and non-pathogens. Lastly, the role of fungal polygalacturonases (PGs) as a virulence factor will be studied by utilizing recombinant antibody technology. The effect of the recombinant antibodies on conidial germination and the infection process will be evaluated.
3. Progress Report
The microflora of nectarine fruit have been isolated over a two-year period and identification of yeast and bacterial isolates is near completion. Thirteen species of yeast have been identified using both genotypic and phenotypic methods. Bacterial strains are being identified using nutritional profiles and fatty acid composition. This research falls within NP 303 – Plant Diseases, Component 4B: Pathogen, Plant, and Antagonist Interactions. Some plant pathogens produce infection structures (appressoria) that are very resistant to chemical fungicides. An artificial membrane system composed of fruit waxes is being developed that will be used to study the interaction between the appressoria of the brown rot pathogen (Monilinia fructicola) and biocontrol agents. The system has been shown to be effective for studying pear and apple pathogens. This research falls within NP 303 – Plant Diseases, Component 4B: Pathogen, Plant, and Antagonist Interactions. In order to develop effective biocontrol strategies, more information is needed about how pathogens interact with their hosts and avoid innate resistance mechanisms. Tissue samples have been collected from peach fruit wounded, wounded-inoculated with a pathogen, and wounded-inoculated with a non-pathogen. Identification of the expressed genes (ESTs) in each of the samples is in progress. This research falls within NP 303 – Plant Diseases, Component 4B: Pathogen, Plant, and Antagonist Interactions. A fungal enzyme (polygalacturanase) involved in the breakdown and infection of fruit tissues has been isolated. Polyclonal antibodies directed against the enzyme have been developed and shown to inhibit the fungal enzyme in a test tube (in vitro). This research falls within NP 303 – Plant Diseases, Component 4B: Pathogen, Plant, and Antagonist Interactions.
5. Significant Activities that Support Special Target Populations
Janisiewicz, W.J., Saftner, R.A., Conway, W.S., Forsline, P.L. 2008. Preliminary evaluation of apple germplasm from Kazakhstan for resistance to blue mold decay caused by Penicillium expansum after harvest. HortScience.43(2):420-426.