ME WISNIEWSKI¹, S DROBY², A EL-GHAOUM ¹ and CL WILSON¹

¹Appalachian Fruit Research Station, USDA-ARS, 45 Wiltshire Road, Kearneysville, WV 25430, USA; ² Dept. Postharvest Science, ARO, The Volcani Center, PO Box 6, Bet Dagan 50250, Israel

Background and objectives
Problems associated with the long-term, extensive use of synthetic pesticides have led to intensified research efforts worldwide to develop alternative control methods that are both effective and also safe for humans and the environment.

In recent years, new avenues of research have been proposed in order to facilitate the development of safer technologies for post-harvest disease control. Among the proposed alternatives, the use of naturally occurring, antagonistic microorganisms has been the most extensively studied, and substantial progress in moving this technology from laboratory to practical application has been achieved. The main hurdle facing this technology in becoming a viable, practical option for the control of post-harvest diseases is its variable efficacy. To provide consistency in performance and economically acceptable levels of control, the addition of low levels of a fungicide (10% of the commercial concentration) has been recommended in combination with the biological preparation. Clearly, there is a need to enhance biocontrol activity by means other than the addition of synthetic fungicides. This present research was aimed at evaluating the use of materials (other than post-harvest fungicides) used routinely as food preservatives to potentially enhance the biocontrol activity of yeast biocontrol agents.

Antifungal food additives have been used for years to control fungal spoilage of foods. They find wide use because they are efficient, cost-effective, readily soluble and have low mammalian toxicity. Food additives are basically chemicals that prevent or interfere with mould growth. These chemicals include: organic acids, salts, fatty acids, antibiotics, essential oils, herbs and spices and various antioxidants.

Results and discusion
An initial in vitro assay was used to rapidly screen a large number of potential inhibitory compounds against spore germination and hyphal growth of Botrytis cinerea and Penicillium digitatum. The compounds that were most effective in the lab bioassay were then tested for their efficacy to inhibit infection and development of P. expansum and B. cinerea on apples and P. digitatum on citrus. In these tests, an evaluation of both the protective and curative activity of the promising compounds was assessed. In many cases, no correlation was found between inhibitory activity obtained in vitro and on the fruit. Among the materials having inhibitory activity against Penicillium and Botrytis, in both in vitro and fruit assays, were sodium bicarbonate, nordihydroguaiaretic acid, poly-D-lysine and poly-D-arginine. A combination of sodium bicarbonate and poly-D-arginine or poly-D-lysine was the most effective in providing both protective and curative activity against P. expansum and B. cinerea on apples. On citrus, however, sodium bicarbonate alone proved to be effective in inhibiting P. digitatum. The use of these materials to enhance the activity of yeast biocontrol agents will be also addressed.