2010 Annual Report
Polygalacturonases are enzymes that are produced by the brown rot pathogen of stone fruit and play a role in virulence. The development of antibodies directed against these enzymes produced by the pathogen is being pursued as a strategy to manage this major postharvest disease of stone fruit. Significant progress has been made in selecting clones expressing antibodies with good affinity to the polygalacturonases prouced by the brown rot pathogen, Monilinia fructicola.
The simple compound, beta-aminobutyric acid (BABA), was demonstrated to induce resistance to brown rot infection in mature peach fruit. Both disease incidence and lesion diameter were reduced in treated samples by 50% compared to untreated, inoculated wounds. The ability to use BABA in combination with yeast antagonists to improve biocontrol efficacy is being evaluated.
The importance of reactive oxygen species (ROS) in plant defense responses against certain pathogens is well documented. There is some evidence that microbial biocontrol agents also induce a transient production of ROS in a host plant which triggers local and systemic defense responses to pathogens. Using laser scanning confocal microscopy, it was observed that the application of M. fructicola and Candida oleophila into citrus and apple fruit wounds correlated with an increase in H(2)O(2) accumulation in host tissue. Living yeast cells were detected in fruit wounds at this time point indicating the ability of M. fructicola to tolerate host ROS, which has been reported to be an intrinsic characteristic of efficient yeast antagonists. Results indicate that the yeast-induced oxidative response in fruit exocarp may be associated with the ability of specific yeast species to serve as biocontrol agents for the management of postharvest diseases.
An apple germplasm collection is maintained at the USDA-ARS-PGRU in Geneva, New York. This collection represents a diverse apple gene pool and was evaluated for resistance to blue mold and bitter rot. Resistance to blue mold was confirmed in select accessions over multiple years. Maturation patterns and quality indices for soluble solids and acidity, which may also affect pathogenicity, were highly variable and reflect the genetic diversity of the germplasm collection. Resistance in four accessions to bitter rot (caused by fungus Colletotrichum acutatum) and two accessions resistant to both diseases are reported for the first time.Janisiewicz, W.J., Conway, W.S. 2010. Combining biological control with physical and chemical treatments to control fruit decays after harvest. Stewart Postharvest Review. 6(1):1-16.
Jurick II, W.M., Vico, I., Gaskins, V.L., Garrett, W.M., Whitaker, B.D., Janisiewicz, W.J., Conway, W.S. 2010. Purification and biochemical characterization of polygalacturonase produced by Penicillium expansum during postharvest decay of ‘Anjou’ pear. Phytopathology. 100(1):42-48.
Vero, S., Garmendia, G., Gonzalez, M., Garat, F., Wisniewski, M.E. 2009. Aureobasidium pullulans as a biocontrol agent of postharvest pathogens of apples in Uruguay. Biocontrol Science and Technology. 19:1033-1049.