Surface ultrastructural studies on the infection process of Pseudocercospora mori causing grey leaf spot disease in mulberry

Pseudocercospora mori produced three kinds of hyphae - primary infection hyphae, internal hyphae and secondary infection hyphae. The primary infection hyphae were developed from conidia and they penetrated the leaf through stomata directly or by lateral penetration branches - the stomatopodia. Inside the stomatal chambers the stomatopodia swelled to become vesicle-like structures. The internal hyphae produced compact stromata in the sub-stomatal chambers. Each stromata carried 1-5 conidia at a time on short unbranched conidiophores. The secondary infection hyphae were developed from internal hyphae directly or from stromata. The secondary infection hyphae emerged through stomata, branched profusely on the leaf surface and produced conidia singly on short conidiophores. The secondary infection hyphae re-entered the leaf directly or by stomatopodia. Conidia were developed also from stomatopodia and from their substomatal vesicles. The conidia developed from substomatal stromata, and those produced from the secondary infection hyphae on leaf surface were similar in their morphology and size of conidiophores. The conidia were obclavate to cylindrical, 3-17 celled and measured 4-35 x 1.5-2 mum. Germ tubes were often found to emerge from the conidial cell nearer to stomata. The primary infection hyphae and secondary infection hyphae produced stomatopodia above stomata.