Accumulation of a phytoalexin in Brassica spp in relation to a hypersensitive reaction to Leptosphaeria maculans

Abstract

A phytoalexin was isolated from the leaves of Brassica juncea cv. Aurea inoculated with Leptosphaeria maculans. Its purification and quantification were carried out by reversed-phase and silica HPLC. The molecular formula of this phytoalexin is C 9H 6N 2S. It prevented spore germination and hyphal growth of L. maculans at 12 μg ml −1 in water. Accumulation of this phytoalexin was also obtained with sprays of AgNO 3 or CuCl 2 solutions. It was not detected in healthy plant tissues, and the effect of cycloheximide suggests that its accumulation is associated with induced plant metabolism. Kinetics of phytoalexin accumulation were compared in B. juncea cv. Aurea (hypersensitive to L. maculans) and B. napus cv. Brutor (susceptible to L. maculans) with CuCl 2 as a non-specific elicitor. The phytoalexin was detected in B. juncea 6 h after challenge and in B. napus 18 h after challenge. Moreover, B. juncea always accumulated more phytoalexin than did B. napus (4 to 10 times more 48 h after elicitation).