Morphology, pathogenicity and isozyme variation amongst French isolatesof Leptosphaeria maculans recovered from Brassica juncea cv. Picra



The characteristics of 36 isolates of Leptosphaeria maculans originating from cv. Picra were investigated using cultural, pathogenicity and isozyme analyses in comparison with six known isolates of A- and B-groups. Picra-related isolates were similar to the three known B-group isolates from Brassica napus using a cultural test. Two known B-group isolates and 29 of the 36 Picra-related isolates tested were aggressive on cv. Picra, whereas all the three known A-group isolates were not. All the 42 isolates tested were aggressive onthe B. napusB. juncea recombinant line MX and on B. napus cv. Westar. Phosphoglucose isomerase analysis showed two different patterns, separating A-group known (fast band) from B-group known isolates (slow band). All cv. Picra isolates displayed the slow band. Considerable differences in isoesterase patterns were found between known A- and B-group isolates. Isolates recovered from cv. Picra displayed six different electrophoretic patterns, including that of the known B-group isolates. Clusters of the 42 isolates, generated by UPGMA analysis based on similarity coefficients of electrophoretic types, matched the previous classification into A- and B-groups, although two atypical Picra-related isolates with a singular pattern clustered with the A-group. The importance of these isolates for blackleg epidemiology and resistance breeding is discussed.