Polymorphism of Tox0Leptosphaeria maculans isolates as revealed by soluble protein and isozyme electrophoresis.
Single-ascospore isolates of L. maculans were characterized according to their sirodesmin PL production in vitro and separated as Tox+ and Tox0 isolates. They were further assessed for their pathogenicity on various crucifers using a cotyledon-inoculation test; their soluble protein patterns obtained by isoelectric focusing; and their profiles following PAGE and visualization of 8 isoenzyme systems. When compared with Tox+ isolates, Tox0 isolates did not show any host specificity since they were able to infect cotyledons of all the analysed crucifer species. In most isoenzyme studies, a few or no common bands were observed between the profiles of Tox0 and Tox+ isolates. Tox+ isolates usually displayed low, or no polymorphism whereas Tox0 isolates displayed high polymorphism as all the analyses separated them into 3 groups corresponding to the NA1, NA2 and NA3 subgroups previously described using RFLP techniques. All the European Tox0 isolates analysed shared similarities with an isolate of the NA1 subgroup. The isoenzymes acid phosphatase, malate dehydrogenase and phosphoglucose isomerase [glucose-6-phosphate isomerase] did not reveal any polymorphism within the NA1 subgroup. In contrast, glutamate oxaloacetate transaminase [aspartate aminotransferase], esterase, glucose-6-phosphate dehydrogenase and shikimate dehydrogenase separated the NA1 isolates into 2-3 subgroups. Finally, a high degree of polymorphism between isolates of the NA1 subgroup was shown following alkaline phosphatase analysis. The possible prevalence of isolates from the NA1 subgroup within the European Tox0 population is discussed.