Glucosinolates in Brassica juncea and resistance to Australian isolates of Leptosphaeria maculans, the blackleg fungus

Abstract

Volatiles released from glucosinolates (predominantly 2-propenyl glucosinolate) in tissues of Brassica juncea and Wasabi japonica are toxic to the blackleg fungus, Leptosphaeria maculans, in vitro. However, there is no relationship between blackleg resistance (in stems or cotyledons) and the level of 2-propenyl glucosinolate in seed or shoot tissue of B. juncea. A representative isolate from each of two classes of Australian isolates of L. maculans was tested: those which cause stem cankers on both B. napus and B. juncea (e.g. isolate MI), and those which cause stem cankers on B. napus but not on B. juncea (e.g, isolate C13). Even in lines of B. juncea in which levels of 2-propenyl glucosinolate were as low as those in B. napus, isolate C13 was still unable to cause stem cankers. This suggests that either 2-propenyl glucosinolate does not play a major role in blackleg disease resistance, or that isolates of L. maculans able to attack B. juncea can detoxify or evade the toxic effects of hydrolysis products from this glucosinolate.