PATHOTYPE AND MOLECULAR CHARACTERIZATION OF MYCOSPHAERELLA GRAMINICOLA ISOLATES COLLECTED FROM TUNISIA ALGERIA AND CANADA
M. Medini, S. Hamza
Septoria leaf blotch, caused by Mycosphaerella graminicola, is one of the most devastating diseases of wheat worldwide. Forty two isolates of M. graminicola, collected from Tunisia, Algeria, and western Canada were characterized according to their virulence behavior and their molecular patterns. Virulence was assessed through the inoculation of four durum wheat and four bread wheat cultivars. Isolates were differentiated into eight pathotypes. Pathotype 1 and 2 were common to Algerian and Canadian isolates. Pathotype 7 was found in Tunisia and in Algeria. Pathotype 8 was specific to Tunisian isolates. Pathotypes 3, 4, 5 and 6 were found only in Algeria. The seven primer pairs used in amplified fragment length polymorphism (AFLP) analysis yielded a total of 194 polymorphic bands. Analysis of AFLP data revealed that genetic diversity within populations (Hs=0.315) accounted for 87.5% of the total genetic diversity (HT= 0.360). The proportion of the total genetic diversity attributable to the population differentiation (GST) was 0.125, reflecting a moderate genetic differentiation between the three populations of M. graminicola. Tunisian and Canadian populations from the Old and the New World displayed almost equal levels of genetic diversity. Algerian population showed the highest genetic diversity possessing 5 private alleles which suggests that it could be a source population where diversity was maintained through cultivation of a broad spectrum of wheat cultivars. The hierarchical classification based on the AFLP analysis separated Tunisian and Canadian isolates whereas the Algerian isolates were distributed in all groups.