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
We demonstrated that direct interactions between the fungus causing brown rot of stone fruits and potentially beneficial bacteria or yeast that occurs on the fruit surface can be studied on parafilm membranes. Many of the bacteria and yeasts that colonized fungus on the membranes provided control of brown rot when applied to fruit under laboratory conditions. The next step is to select those antagonists that are best adapted to conditions occurring during storage and handling of the fruit. Screening was continued on the apple germplasm collection maintained at the USDA-ARS-PGRU in Geneva, New York, for resistance to postharvest diseases. Two new accessions resistant to blue mold were identified: 1) an accession of Malus orientalis from the Caucus region of the former Soviet Union and 2) an accession of Malus sylvestris of an unknown origin. The identification of blue mold resistance in these accessions are in addition to the previously reported accessions of Malus sieversii. Brown rot disease (Monilinia fructicola Honey) is a major cause of Prunus spp. fruit losses in pre- and post-harvest settings. As part of an ongoing effort to develop biological approaches for managing diseases of temperate fruit crops, we are seeking to better understand the mechanisms by which M. fructicola suppresses or overcomes defense reactions in stone fruit. To identify genes specifically induced/repressed during stone fruit-postharvest pathogen interaction, a microarray analysis was conducted of peach fruit transcriptome response to compatible (M. fructicola) and non-compatible (Penicillium digitatum) pathogens. A recently developed apple microarray consisting of 40,000 70-mer-oligos was used to hybridize RNA extracted from fruit tissue 24 h after wound inoculation with a conidial suspension of M. fructicola, P. digitatum, or sterile water. Tissue from intact fruit was also analyzed. Statistical analysis of the data generated by a total of 16 microarrays showed that 1,048 genes are differently regulated in peach fruit in response to M. fructicola and P. digitatum inoculation. From those, 552 were uniquely regulated by brown rot pathogen, while P. digitatum specifically affected the expression of 493 peach genes within the first 24 h after inoculation. Genes associated with resistance responses were identified and categorized. Disruption of the resistance response was associated with a strong oxidative burst. Further understanding of how the pathogen interferes with host resistance is in progress.
1. Identified hydrogen peroxide as an effective indicator for biocontrol of postharvest rots. An increased understanding of how postharvest biocontrol systems work is essential to improve their effectiveness and commercial viability. ARS researchers at Kearneysville, WV, in collaboration with scientists at the Agricultural Research Organization (ARO), Israel, discovered that when yeast bicontrol agents are applied to wounded fruit, there is a large production of hydrogen peroxide by the yeast and the host. This burst of hydrogen peroxide, known as an oxidative burst, triggers resistance in the fruit making them less susceptible to pathogens that cause postharvest rots. This information will help in the selection of superior bicontrol agents that can be used to effectively replace the use of postharvest fungicides.
2. Identified apple germplasm with postharvest disease resistance. Postharvest decay of fruits and vegetables results in substantial economic losses to suppliers and consumers. Little postharvest disease resistance exists in commercial varieties of apple. ARS researchers at Kearneysville, WV, and Beltsville, MD, have screened apple germplasm collected from around the world and maintained at USDA-ARS, Apple Germplasm Repository, Geneva, NY, and identified several novel sources of postharvest disease resistance. These selections can be used in apple breeding programs to conduct basic research on disease resistance and highlights the importance of the genetic diversity present in the germplasm collections.
Liu, J., Wisniewski, M.E., Droby, S., Tian, S., Tworkoski, T. 2011. Effect of heat shock treatment on stress tolerance and biocontrol efficacy of Metschnikowia fructicola. FEMS Microbiology Ecology. 76:145-155.