Characterization and pathogenicity of isolates ofLeptosphaeria maculansfrom Aguascalientes and Zacatecas, Mexico1

Blackleg of crucifers caused by Leptosphaeria maculans is the most important disease of broccoli and cauliflower in central Mexico, causing up to 70% yield loss in cauliflower crops. The pathogen was isolated from broccoli crops near Aguascalientes, Ags., and Zacatecas, Zac., and culture characteristics and pathogenicity on cauliflower were examined. Colony appearance and mycelial growth on V8-juice agar, germ tube growth on water agar, and the absence of pigment production in Czapek-Dox medium were characteristic of isolates belonging to the aggressive strain. No pseudothecia formed when the Mexican isolates were paired nor when they were crossed with a tester isolate for mating type +, suggesting that all of the Mexican isolates were of mating type +. This was indirectly confirmed by the absence of the MAT-2 gene, which is associated with mating type –. Reliable inoculation techniques, based on inoculation of wounded plants with pycnidiospores, were developed for cauliflower. In seedlings whose cotyledo...