GENETIC-CHARACTERIZATION OF AVRLM1, THE FIRST AVIRULENCE GENE OF LEPTOSPHAERIA-MACULANS

Specific interactions of the fungal pathogen Leptosphaeria maculans wi th Brassica napus cultivars were observed when the cultivars were inoc ulated with isolates belonging to pathogenicity groups (PG) PG3 and PG 4. PG3 isolates induced resistance responses on cotyledons or leaves o f cv. Quinta, whereas PG4 isolates caused sporulating lesions on this cultivar. In contrast, both pathotypes caused disease symptoms on cvs. Westar and Glacier. The genetic basis of cultivar specificity was stu died using tetrad analysis after in vitro crosses between one PG3 and one PG4 isolate. For the genetic study, the use of random amplified po lymorphic DNA (RAPD) as genetic markers was assessed. Of 61 primers, 1 0 generated reproducible polymorphisms. Of these, 9 generated 18 RAPD markers displaying a 2:2 segregation ratio within the 10 analyzed tetr ads. A 2:2 segregation ratio for avirulence/virulence to cv. Quinta al so was observed in the progeny. Consequently, the single genetic locus controlling cultivar specificity on Quinta was considered the first a virulence gene described in L. maculans and was designated AvrLml.