1a. Objectives (from AD-416):
1: Develop effective biologically based systems for managing postharvest disease of temperate fruit crops. 1.A. Establish a biocontrol system to control brown rot of stone fruits. 1.B. Determine the cytological aspects of resistance in wild apple fruit from Kazakhstan to blue mold. 1.C. Develop a biocontrol management system for gray mold and anthracnose of strawberry high-tunnel production utilizing UV-C and microbial antagonists. 2: Develop knowledge base on the biology of postharvest biocontrol systems for use in selecting superior antagonists and to improve the overall efficacy of biocontrol agents. 2.A. Determine the effect of yeast induced reactive oxygen species (ROS) on host resistance. 2.B. Determine mechanisms associated with biocontrol of brown rot of stone fruits.
1b. Approach (from AD-416):
Research is focused on reducing the need of using postharvest fungicides in fruit production. It includes developing postharvest biological control of brown rot latent infections of stone fruits, basic studies on biocontrol systems, explaining the cytological basis for the resistance of Malus sieversii (‘Kazak’) apples to blue mold, and using LED lights to reduce gray mold and anthracnose of strawberries in high tunnel cultures. The seasonality of fruit availability allows the project to address the different objectives. Biocontrol studies on stone fruits will be conducted in early summer, resistance research on Kazak apples in the fall, and biocontrol studies on strawberry during the winter. Biocontrol of latent infections will include scale-up tests under simulated commercial conditions and research explaining the mechanism of biocontrol. Resistance studies of ‘Kazak’ apples will focus on characterizing the biochemistry of wound responses. Strawberry research will involve determining the effect of different UV-LED wavelengths on survival of B. cinerea and Colletotrichum spp., and epiphytic microflora, its effect on plants, and the use of selected LED in combination with antagonists to reduce gray mold and anthracnose. Basic research on yeast-based biocontrol systems will determine the effect of reactive oxygen species (ROS) on the efficacy of yeast antagonists and the ability of yeast ROS to induce defense systems in apple. This research will give growers alternative biological tools to combat fruit diseases, improve the efficacy of biocontrol systems, and in the case of the Kazak work, provide new information for the basis of postharvest disease resistance in apple germplasm that can be used in breeding programs.
3. Progress Report:
The healing ability of fruit wounds were determined for wild apples from Kazakhstan and Central Asia. We found that some of these apples have remarkably fast healing ability that prevented decay causing fungus from penetrating fruit wound, the normal entry for the fungus, and causing fruit decay. The speed of the resistant reaction coincided with an increase in production of reactive oxygen species (ROS), molecules that are involved in plant resistant reactions to invading fungi. Ultraviolet light (UV-C) was used to kill fungi that can cause decay of strawberry fruit. Under laboratory conditions using certain manipulations in applying UV-C, we achieved a much better kill of the fungi than using a standard irradiation method. Since the UV-C irradiation at high doses can be damaging to plants, results of our research allowed us to lower the amount of UV-C irradiation of plants below a threshold that causes injury and at the same time be strong enough to kill the fungus. Developing alternative approaches to disease control is a critical objective of NP-303, Plant Diseases, due to consumer demands to lower exposure to chemicals and reduce the impact of agriculture on the environment. In the past decade, USDA-ARS has identified several species of yeasts that can be used as biocontrol agents against postharvest diseases of fruit. Despite these options, use of these products remains limited partly due to variable performance. Therefore, there is a need to better understand the biology of biocontrol systems (host-pathogen-biocontrol agent) in order to increase their efficacy under a wide array of environmental conditions. In the present study, the expression of an apple disease resistance gene (PR-8) in response to the grey mold pathogen (Botrytis cinerea) was examined and whether the secretion of the coded protein could enhance the biocontrol activity of a yeast was evaluated. The PR-8 gene from apple was cloned and put in a yeast expression system. Results indicated that PR-8 is upregulated in response to the grey mold pathogen and is also stimulated by a yeast biocontrol agent. Futhermore, when the gene was expressed in a yeast, the yeast inhibited the grey mold pathogen both in a test tube system and in apple fruit. This information will be used to develop strategies to increase natural resistance in harvested apple fruit and increase the efficacy of yeast biocontrol agents.
Janisiewicz, W.J., Jurick II, W.M., Vico, I., Peter, K.A., Buyer, J.S. 2012. Culturable bacteria from plum fruit surfaces and their potential for controlling brown rot after harvest. Postharvest Biology and Technology. 76:145-151.