A Phytoalexin Type of Reaction in the Botrytis Infection of Leaves of Bean (Vicia faba L.)

Abstract

Botrytis fabae and B. cinerea produce discrete brown lesions on the leaves of bean (Vicia faba); but in high humidity the lesions caused by B. fabae spread although those caused by B. cinerea do not. Attempts to explain this difference in terms of interactions between the cell-wall hydrolysing enzymes of the fungi and the phenolic compounds of the host failed¹. Müller² suggested that abnormal metabolites, called phytoalexins, are formed when plant cells are invaded by fungi. Phytoalexins are fungitoxic and may be part of the defence system of the plant. Cruickshank and Perrin³ isolated from infected pea tissue a phytoalexin, called pisatin, which was fungistatic at the concentrations in which it appeared in the infection drops. Non-pathogens of peas caused the formation of pisatin in concentrations above its ED₅₀ value, and pathogens that of pisatin below its ED₅₀ value toward the fungi in these two groups in vitro⁴.