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United States Department of Agriculture

Agricultural Research Service

2011 Annual Report

1a.Objectives (from AD-416)
Objective 1: Elucidate the role of fungal extracellular enzymes as virulence factors important in postharvest decay of fresh fruit including the effect of pathogen modification of the host environment on virulence factors.

Objective 2: Evaluate potential control strategies targeting fungal extracellular enzymes to reduce postharvest decay of fresh fruit. Sub-objective 2.A. Optimize the application of recombinant antibodies targeting extracellular enzymes of P. expansum and P. solitum to reduce postharvest decay of pome fruits. Sub-objective 2.B. Determine the effect of antioxidants and their analogs on decay development.

1b.Approach (from AD-416)
To elucidate the role of fungal extracellular enzymes as virulence factors in postharvest decay of apple and pear fruit, we will first compare the ability of several strains of a highly virulent and a weakly virulent pathogen of the same genus to produce extracellular enzymes (such as polygalacturonases and cellulases) during fruit infection and in response to fungal modification of the host/pathogen microenvironment. 'Golden Delicious' apple and 'Anjou' pear fruit will be infected with P. expansum or P. solitum and we will extract, purify, and characterize the extracellular enzymes produced by these organisms using standard procedures. We will develop and utilize recombinant antibodies specific for binding to and inactivating enzymes produced by the pathogens in vivo and in vitro. The antibodies will allow us to determine which specific enzymes play a major role in virulence of Penicillium species on pome fruit. Strategies incorporating recombinant antibodies against virulence factors, antioxidants known to have anti-fungal activity, and mild stress treatments will be tested for their ability to control postharvest decays of pome fruits caused by Penicillium species.

3.Progress Report
Maintaining the quality of apple and pear fruit by eliminating decay in long-term storage is critical to prevent postharvest losses. ARS scientists at Beltsville, MD, have determined that Penicillium solitum is capable of decaying apple fruit by making them more acidic and producing a protein (polygalacturonase) that is responsible for softening the fruit tissue. This information may be used by plant pathologists to design new disease control strategies that alter the fruit surface and or inhibit fruit decay.

Resistance to blue mold has been evaluated in a collection of wild apple fruit trees located in Geneva, New York. We have identified 19 of 452 different wild apple fruit that are resistant to the fungus that causes blue mold (Penicillium expansum). Of these nineteen, four were resistant from year to year which is a valuable characteristic as these same fruit can then be used for further study. This information will be beneficial to plant breeders and molecular geneticists interested in characterizing and/or incorporating resistance into commercial apple cultivars.

Understanding the basic mechanisms that the blue mold fungus (P. expansum) uses to cause apple and pear fruit decay are important for uncovering new ways to halt postharvest decay. We have determined that P. expansum can grow and produce an enzyme responsible for tissue maceration (polygalacturonase) on a wide variety of nutrient sources and that a single enzyme is produced in the presence of apple pectin. This fundamental information on enzyme production may aid other scientists in designing new postharvest decay control strategies.

ARS scientists at Beltsville, MD, have kept in close communication with the apple and pear fruit growers and packers. We have sampled decayed fruit from storage bins in their state-of-the-art storage facility. These fungi will be used to characterize their sensitivity to commonly used postharvest fungicides. It is important to conduct fungicide sensitivity tests to determine if they are developing resistance to the chemicals used to control decay in storage. This information will directly benefit other scientists and the packing industry as it may lead to fungicide management implications.

1. Low temperature storage of apple fruit delays blue mold decay. We demonstrated that storing fruit at 0°C after harvest delays decay by affecting fungal growth compared to other temperatures (5, 10, and 20°C) used for storing intact and fresh cut fruit. It was also determined that PG enzyme activity was affected by temperature which explains why tissue maceration of inoculated apple fruit was deterred. The impact of this accomplishment is that this information may then be used by other scientists to target specific biological processes in this fungus which could be used to control decay.

2. Purification of Polygalacturonase (PG) from P. expansum and P. solitum-decayed apple and pear fruit. We extracted and purified PGs from P. expansum and P. solitum-decayed pear and apple fruit tissue. We found that both fungi produced a single enzyme in decayed tissue that differ in their abilities to function at various pHs and also at various incubation temperatures. We also demonstrated that the purified PGs are capable of macerating host tissue. The impact of this accomplishment is that this knowledge may be applied either through genetic manipulation of the host (apple) or by identifying PG inhibitors that may be applied to the fruit surface to block decay.

Review Publications
Vico, I., Jurick Ii, W.M., Camp, M.J., Janisiewicz, W.J., Conway, W.S. 2010. Temperature suppresses decay on apple fruit by affecting Penicillium solitum conidial germination, mycelial growth and polygalacturonase activity. Plant Pathology Journal. 9(3):144-148.

Jurick Ii, W.M., Janisiewicz, W.J., Saftner, R.A., Vico, I., Gaskins, V.L., Park, E., Forsline, P.L., Fazio, G., Conway, W.S. 2011. Identification of wild apple germplasm (Malus spp.) with resistance to the postharvest decay pathogens Penicillium expansum and Colletotrichum acutatum. Plant Breeding. 130:481-486.

Last Modified: 4/19/2014
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