GENETIC-ANALYSIS AND IDENTIFICATION OF AMPLIFIED FRAGMENT LENGTH POLYMORPHISM MARKERS LINKED TO THE ALM1 AVIRULENCE GENE OF LEPTOSPHAERIA-MACULANS

A gene-for-gene interaction was previously suggested by mapping of a s ingle major locus (LEM 1) controlling cotyledon resistance to Leptosph aeria maculans isolate PHW1245 in Brassica napus cv. Major. In this st udy, we obtained further evidence of a gene-for-gene interaction by st udying the inheritance of the corresponding avirulence gene in L. macu lans isolate PHW1245. The analysis of segregating F-1 progenies and 14 test crosses suggested that a single major gene is involved in the in teraction. This putative avirulence gene was designated alm1 after the resistance locus identified in B. napus. Amplified fragment length po lymorphism (AFLP) markers were used to generate a rudimentary genetic linkage map of the L. maculans genome and to locate markers linked to the putative avirulence locus. Two flanking AFLP markers, AC/TCC-1 and AC/CAG-5, were linked to alm1 at 3.1 and 8.1 cM, respectively. Identi fication of markers linked to the avirulence gene indicated that the d ifferential interaction is controlled by a single gene difference betw een parental isolates and provides further support for the gene-for-ge ne relationship in the Leptosphaeria-Brassica system.