Submitted to: Journal of American Society of Horticulture Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 10, 1997
Publication Date: N/A
Interpretive Summary: While synthetic fungicides prevent colossal losses to food crops, they also are hazardous and can cause environmental pollution and damage wildlife. Naturally occurring and/or non-toxic, environmentally safe inhibitors of fungal growth and development need to be identified to reduce our dependence on traditional, albeit hazardous, fungicides. We found that a postharvest combination treatment of apples with calcium and nonhazardous, target-specific inhibitors of fungal growth and development, DFMO or DFMA, effectively controls (about 90 percent) postharvest decay caused by the two most serious postharvest pathogens of apples. Less than 10 g of inhibitor is needed to effectively treat a ton of fruit. The postharvest combination treatment with calcium and target-specific inhibitors of fungal pathogens presents apple growers with an interesting alternative to the hazardous traditional fungicide currently in use to control postharvest decay in apples.
Three polyamine biosynthesis inhibitors, alpha-difluoromethylornithine (DFMO), alpha-difluoromethylarginine (DFMA) and alpha-methylornithine (MeOrn), alone and in combination with calcium chloride, were tested for their ability to reduce in vitro growth and soft rot development in apple (Malus domestica Borkh.) fruit caused by Botrytis cinerea Pers.:Fr. and Penicillium expansum Link. All three inhibitors reduced the in vitro growth of the pathogens. Calcium had no effect on fungal growth in vitro. Pressure infiltration of millimolar concentrations of DFMO or DFMA or 2.5 percent (w/v) calcium chloride solutions into apples reduced subsequent soft rot development by both B. cinerea and P. expansum more than 40 percent. A combination treatment of Ca and DFMO or DFMA reduced decay more than 67 percent. Treatment of apples with MeOrn was less effective at inhibiting decay development. None of the inhibitors affected polyamine levels in apple cortical tissues. Some injury to the fruit surface was observed with both Ca and MeOrn treatments. Fruit treated with Ca and any of the inhibitors were less firm than those treated with Ca alone. Specific polyamine biosynthesis inhibitors in combination with calcium may prove useful in reducing postharvest decay in apples.