Association mapping in Brassica napus (L.) accessions identifies a major QTL for blackleg disease resistance on chromosome A01
Variation in the responses of selected genotypes of spring rape to infection by a wide range of isolates of Leptosphaeria maculans was analyzed in this study. Differences in severity of disease damage to seedlings between host and pathogen genotypes were highly significant. Interactions between host and pathogen were also highly significant. The generally resistant cultivar Wesreo was susceptible to a number of isolates whereas the normally susceptible cultivars Zollern-gold and Ceska were resistant to some isolates. Overall, however, Wesreo was resistant to a far greater number of isolates than were the susceptible genotypes. Significant differences in severity of disease damage were also observed between groups of isolates from different sites. All host genotypes were resistant to a substantially greater proportion of isolates from certain sites than from others. Interactions were again detected in that the ranking of sites on the basis of the proportion of isolates causing severe damage varied between host genotypes. The significance of host-pathogen interactions in the B. napus-L. maculans relationship is discussed with special reference to current views on the nature of horizontal resistance.