Studies on Symptomatology, Morphology and reactions of Some Soybean Cultivars to the Downy Mildew Fungus

Abstract

Soybean plants exhibited systemic and local infections to downy mildew fungus, Peronospora manshurica (Naoum.) Syd. Systemically infected plants sometimes die prematurely, or spindly, grow and produce few seeds, some plants still exhibit foliar symptoms and most of seeds are infected. Systemically infected plants produce conidia which become windborne and initiate local infections in new areas. The fungal mycelium grows within the plant. Conidia are round to oval, produced on dichotomously branched conidiophore from stomata. Antheridium, oogonium and oospore are found on both leaf and seed. Field observation on 506 cultivars in dry and rainy seasons of 1975-1976 showed that symptoms on 77 cultivars are severe, on 78 moderately severe and 351 had none.