GLUCOSE PHOSPHATE ISOMERASE POLYMORPHISMS DISTINGUISH WEAKLY VIRULENT FROM HIGHLY VIRULENT-STRAINS OF LEPTOSPHAERIA-MACULANS

Of 92 isolates of Leptosphaeria maculans from six countries, 68 contained a single isozyme of glucose phosphate isomerase (GPI) that moved 70 mm after 11 h of starch gel electrophoresis and 24 contained a single isozyme of GPI that moved 65 mm. Isolates with fast or slow isozymes of GPI were classified as electrophoretic type (ET) 1 or 2, respectively. The mean lesion length produced by ET2 isolates inoculated into stems of canola (double haploid plants derived from Brassica napus cv. Westar) differed significantly from that of ET1 isolates. However, lesion lengths of the most virulent of the ET2 isolates and of the least virulent of the ET1 isolates were not significantly different and cluster analysis of lesion lengths did not separate the collection of isolates into two groups coincident with electrophoretic type. Similarly, neither optical density nor pH of spent culture medium divided the isolates into two distinct groups. Only GPI isozyme polymorphisms separated the collection unequivocally into two groups, ET1 and ET2, which had the general characteristics of the highly virulent and weakly virulent strains of L. maculans.