Pearl millet downy mildew (Sclerospora graminicola): Zoosporogenesis

Summary Cleavage of the zoosporangial cytoplasm ofSclerospora graminicola, the causal agent of pearl millet downy mildew, is by means of the fusion of cleavage vesicles and vesicles containing the extruded axoneme with the cell membrane. This type of zoosporogenesis linksS. graminicola to other Peronosporalean species, and is very similar to that seen for all uniflagellate species examined to date, while it separates it from species of theSaprolegniales where zoosporogenesis is brought about by the expansion of the central vacuole, or where the plasmalemma alone is used.The origin of the cleavage vesicles appears to be from the dictyosomes and not from the finger-print bodies which are rapidly formed in large numbers after axoneme formation and after the cleavage. vesicles have started to appear in the cytoplasm.     

Changes in total phenolic contents of pearl millet callus resistant and susceptible to downy mildew

Tissue cultures were used as the host-parasite systems to study the total phenolics in relation to downy mildew infection in pearl millet. Total phenolics increased due to infection bySclerospora graminicola. As the age of the callus tissue increased, an increase in total phenolics was observed in both susceptible and resistant cultivars. The possibility of using a dual culture to study the biochemical changes occurring in the host-parasite interactions of an obligate parasite is discussed.     

Detection of Seed-Borne Inoculum of Peronosclerospora sorghi in Sorghum

An alkali maceration technique has been developed to detect internally seed-borne inoculum of Peronosclerospora sorghi in sorghum seeds. Optimum period for maceration was found to be 36 h. Oospores in the glumes and mycelia in the pericarp and endosperm were clearly demonstrated. Mycelium was found in the pericarp of 40 % of the seeds tested and in the endosperm of 5 % of seeds. The possibility of using this technique to detect seed-borne downy mildew infection has been emphasized.