The development of different pathotype groups of Mycosphaerella pinocles in susceptible and partially resistant pea leaves

The progress of infection by high- and low-virulence isolates of Mycosphaerella pinodes was examined in susceptible and partially resistant pea leaves. Conidia germinated with one or more germ tubes which frequently branched and formed appressorium-like structures on the leaf surface. Penetration occurred through the epidermal walls. A structure similar to an infection vesicle was formed, lying partly in the epidermal wail and partly in the cell lumen. From this structure, a penetration hypha was derived which initiated the development of the intra- and intercellularly-growing fungal colony. Infections led to rapid tissue collapse in both susceptible and resistant interactions. In resistant interactions, the formation of infection vesicles and penetration hyphae was reduced, and the development and spread of lesions was retarded.