A MODIFIED METHOD FOR DETECTING OOSPORES OF PERONOSCLEROSPORA SORGHI, THE CAUSAL ORGANISM OF SORGHUM DOWNY MILDEW IN SUDAN GRASS SEEDS (SORGHUM SUDANENSE)

The washing technique was developed for detecting oospores of the sorghum downy mildew (Peronoscierospora sorghn on seed surface or in fine plant debris (seed transmitted infection) in sudan grass (Sor­ghum sudanense). Modification was based on grinding the seed bulk for 2 min before washing followed by I ifferation,centrifugation and adding drops of iodine tincture to the washing sediments. Grinding increased the number of oospores in washing sediment from the different seed parts , i.e., glumes , pericarp or perianth as well as from plant debris. On the other hand , iodine tincture stained the starch particles, prolonged the time provided for microscopic examination and made the examination easier than in the common technique. Although mycelium was observed also in some different seed parts, especially the endosperm tissues, the internal infection (endosperm and scutellum) could not be confirmed yet. Systemic infection of plants produced from infested seeds was proved in the greenhouse using sterilized soil (pathogen-free). Mean­while, no systemic infection was observed in plants resulting from non-infested seeds. Moreover, soaking sudan grass seeds in a suspension of the fungicide Apron (metalaxyl) at Concentration of 750 ppm for 2 hours before sowing ,increased the emergence and reduced seed trans­mission of Peronosclerospora sorghi.