Morphological and virulence variation among isolates of Mycosphaerella pinodes the causal agent of pea leaf blight

Abstract

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 × 143 µm to 280 × 265 µm and from 11.5 × 2.3 µm to 22.5 × 6.3 µm 
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.