Morphological and virulence variation among isolates of Mycosphaerella pinodes the causal agent of pea leaf blight
Résumé
Mycosphaerella blight caused by Mycosphaerella pinodes (Berk. and Blox.) Vestergr. is an important disease, causing severe damage in peas. Variability of 20 Algerian isolates of M. pinodes representative of four agro climatic regions were investigated on the basis of cultural, morphological and pathogenicity. Culture and morphology showed variations in colony color, radial growth pattern and production of pycnidia and pycnidiospores. Significant differences (P < 0.05) in both pycnidia and pycnidiospores size among isolates were observed. Hence, the size of pycnidia and pycnidiospores of M. pinodes varied from 145 x 143 mu m to 280 x 265 mu m and from 11.5 x 2.3 mu m to 22.5 x 6.3 mu m respectively. Using the factor analysis, this revealed that the first principal component (pc) was more related to the growth and sporulation aspect, hence, the colony growth and both the pycnidia and pycnidiospore density were more related to the first pc, while the second pc contributed for the pycnidiospores size. The isolates were also evaluated for their pathogenicity on seven cultivars in controlled conditions. Cluster analysis based on disease rating on a scale of 1 to 5, indicated higher similarity coefficient. In addition, using Euclidian distances method, the clusters were subdivided at 70% of similarity in seven pathotype groups (PG). The two first pathotypes grouped the most isolates (70%), representing isolates from the four agro climatic regions. However, the members of same group were different in their cultural and morphological characteristics. A detailed study to investigate molecular and genetic basis of diversity is suggested.