Circumstantial evidence for phytoalexin involvement in the resistance of peanuts to Aspergillus flavus

Abstract

Three stilbene phytoalexins, elicited by slicing and incubating imbibed peanut kernels under aerobic conditions, inhibited spore germination and hyphal extension of Aspergillus flavus with ED50 values in the range 4.9-12.8 μg ml-1. Phytoalexin yield was dependent on cultivar, conditions and duration of incubation after slicing, and crop history. The yield of phytoalexin from ten cultivars studied, after slicing and incubating at 25°C for 24 h, ranged from 28 to 935 μg per g fresh weight and was negatively correlated with dry kernel colonization by A. flavus [r = -0.868 when plotted as ln (phytoalexin concn) against ln (percentage peanut colonization)]. When the incubation period was extended to 96 h there was no such correlation. Reduced phytoalexin yields were obtained when sliced kernels of one cultivar studied were incubated in water or at 37°C, and no phytoalexin was obtained when the slices were incubated under nitrogen gas or frozen before aerobic incubation. Drought stress during pod development in four cultivars studied reduced phytoalexin yields of sliced kernels incubated at 25°C for 24 h by 17-65% compared with non-stressed controls.