Another downy mildew of the genus Peronosclerospora on maize has now been isolated in Nigeria, but the downy mildew disease of maize, caused by Peronosclerospora sorghi, is presently the most damaging maize disease in Nigeria. The maize strain of the pathogen is thought to survive during the dry season on maize cultivated in hydromorphic valleys in southwestern Nigeria. Kernels harvested from a heavily infected farmer's field were subjected to histological studies which clearly revealed the presence of mycelium in the endosperm, scutellum, and near the embryo of the maize kernels. Two susceptible maize varieties and a cultivar of sweet corn have been observed for further evidence of internally seed-borne P. sorghi viz: (1) Pool-16, (2) Funtua-88TZSR-W (3) Sweet corn (Golden bantam). Peronosclerospora sorghi mycelia were observed in the kernels of the three. Most Nigerian small-scale farmers buy seed from the local market or use their saved seed. When the seed is not properly dried, mycelium may remain viable and could be a source of primary infection. Inoculum within seeds is an important means by which many pathogens reach areas hitherto free from disease. Seed-borne mycelium could be one mode of survival of this pathogen and it could account for the recent sporadic spread of downy mildew in southwestern Nigeria. The risk of transmitting maize downy mildew via living mycelium in dried seed is currently being investigated.

English

9801|AGRIS 9702

Jose Juan Caballero

CIMMYT Publications Collection