Gametogenesis and oospore formation in Sclerospora species on Sorghum vulgare.

The downy mildew of Sorghum vulgare Pers., first described by Kulkarni (2) in India under the name Sclerospora graminicola (Sacc.) Schroet. var. andropogonis-sorghi Kulk., was later raised to specific rank by Weston and Uppal (9) as vS\ sorghi (Kulk.) Weston & Uppal. In a recent paper, the authors pointed out (5) that since the epithet var. andropogonis-sorghi used by Kulkarni had priority, the correct name of the fungus was 5\ andropogonis-sorghi (Kulk.) Kulk. This fungus was shown by the investigations of Kulkarni, Uppal and Weston to differ morphologically and biologically from Sclerospora graminicola (Sacc.) Schroet. The type of branching of the conidiophores and method of germination of the conidia in the two species were observed to be differ? ent. Failure of conidia or oospores from S. andropogonis-sorghi to cross-infect Pennisetum typhoideum L., the chief host for S\ graminicola in India, was considered as an additional evidence for separating the two species. No cytological details involved in the gametogenesis and oospore formation for 5*. andropogonis-sorghi are known in order to institute any comparison with 5\ graminicola. It may be pointed out that in the genus Albugo the cytological details in gametogenesis and oospore formation have offered a very reliable means of confirming species differentiation. In the present study gametogenesis and oospore formation in *S\ andropogonis-sorghi were investigated and opportunity was taken to make comparative studies with S. graminicola and Sclerophthora macrospora (Sacc.) Thirumalachar et al., which until recently was placed under Sclerospora as S. macrospora. Leaves of Sorghum vulgare affected with S. andropogonis-sorghi were collected in various stages of development and fixed in the follow? ing fixatives: formalin-acetic-alcohol, and Belling's modification of Navaschin's fluid, with or without pre-treatment with Carnoy's fluid. Paraffin sections 6-10 fx thick were cut and stained with Newton's