Abiotic elicitation of indole phytoalexins and resistance to Leptosphaeria maculans within Brassiceae

Forty three accessions of Brassica species and one each of Sinapis and Raphanus were assessed for (i) resistance to Leptosphaeria maculans according to a coty-ledon-inoculation test and (ii) indole phytoalexin accumulation following abiotic elicitation with CuCl2. Five indole phytoalexins were determined in the lines following elicitation. Brassilexin, cyclobrassinin and cyclobrassinin sulphoxide were found within at least some lines of all species, whereas brassinin was only detected in B. oleracea and B. napus and methoxybrassinin within these two species and B. rapa and B. carinata. None of the five indole phytoalexins could be found in Raphanus sativus or Sinapis alba. The accumulation of large amounts of specific phytoalexins could be correlated with the presence of the different Brassica genomes. Lines possessing the B genome (B. nigra, B. juncea and B. carinata) which accumulated high amounts of brassilexin, displayed a hypersensitive resistance to Infection whereas the majority of lines of B. oleracea, B. napus and B. rapa which did not accumulate large amounts of brassilexin, were susceptible. However, a B. nigra and a B. rapa line which only accumulated low amounts of brassilexin were highly resistant to the pathogen. Neither the accumulation of the Other phytoalexins nor the total accumulation of indole phytoalexins could be related to resistance to L. maculans.