POLYMORPHISM OF TOX(O) LEPTOSPHAERIA-MACULANS ISOLATES AS REVEALED BYSOLUBLE-PROTEIN AND ISOZYME ELECTROPHORESIS

Single-ascospore isolates of Leptosphaeria maculans were characterized according to their sirodesmin PL production in vitro and separated as Tox(+) and Tox(0) isolates. They were further assessed for (i) their pathogenicity on various crucifers using a cotyledon-inoculation test; (ii) their soluble protein patterns obtained by isoelectric focusing; and (iii) their profiles following polyacrylamide electrophoresis and visualization of eight isozyme systems. As compared to Tox(+) isolate s, Tox(0) isolates did not show any host specificity since they were a ble to infect cotyledons of all the analysed crucifer species. In most isozyme studies, a few or no common bands were observed between the p rofiles of Tox(0) and Tox(+) isolates. Tox(+) isolates usually display ed low, or no polymorphism whereas Tox(0) isolates displayed a high po lymorphism as all the analyses separated them into three groups corres ponding to the NA1, NA2 and NA3 subgroups previously described using R FLP techniques (Koch el al., 1991). AU the European Tox(0) isolates an alysed shared similarities with an isolate of the NAI subgroup. Three isozymes, i.e., acid phosphatase (ACP), malate dehydrogenase (MDH) and phosphoglucose isomerase (PGI) did not reveal any polymorphism within the NA1 subgroup. In contrast, glutamate oxaloacetate transaminase (G OT), esterase (EST), glucose-6-phosphate dehydrogenase (G6PDH) and shi kimate dehydrogenase (SKD) separated the NA1 isolates into two to thre e subgroups. Finally, a high degree of polymorphism between isolates o f the NA1 subgroup was shown following alkaline phosphatase (ALP) anal ysis. The possible prevalence of isolates from the NA1 subgroup within the European Tox(0) population is discussed.