Factors affecting infection by Peronosclerospora sorghi on sorghum

Abstract

Age of sorghum plants is important in the development of downy mildew disease incited by Peronosclerospora sorghi. Plants inoculated just after emergence and up to 4-5 leaf stage are highly susceptible. In plants inoculated after 6-7 leaf stage, systemic symptoms were not observed but only local lesions appeared. Conidial concentration of 40/seedling brings about 100% infection if the host seedlings are inoculated through root. Systemic infection occurs in 10 and 22 days depending upon the conidial concentration. Roots of the seedlings inoculated with 1000 conidia/seedling get infected earlier. Mature conidia are highly infective compared to immature or old conidia. Soil and seed-borne inoculum can initiate both systemic and local lesion type of symptoms at any growth stage of the host plant in addition to air-borne conidia. Late expression of systemic infection can result both from air-borne conidia and oospore present in the soil or seed.