Glucosinolates and disease resistance in oilseed rape (Brassica napus ssp. oleifera)

The hypothesis that enhancing the level of glucosinolates in leaves of oilseed rape would increase resistance to two fungal pathogens was tested. Thirty-three Brassica napus lines with variable leaf glucosinolate contents were assessed for susceptibility to infection by Leptosphaeria maculans and Alternaria spp. under field conditions. The data clearly showed that there was not a simple positive relation between glucosinolate content and resistance, and that the hypothesis can be refuted. The level of Alternaria infection of both leaves and pods was positively correlated with glucosinolate content, while for L. maculans there was no significant relationship between the two variables. It is suggested that these pathogens have become specialists on glucosinolate-containing taxa in an analogous way to insect herbivores.