Fertility and Mating Type Frequency in Indian Isolates of Sclerospora graminicola, the Downy Mildew Pathogen of Pearl Millet.

Sclerospora graminicola, the downy mildew pathogen of pearl millet, is an oomycetous obligate parasite which reproduces by both sexual and asexual means. Fertility and mating type frequencies were studied in 70 single-zoospore isolates (SZIs) obtained from seven representative oo-sporic isolates (Sg 021, Sg 048, Sg 110, Sg 139, Sg 149, Sg 152, and Sg 153) of S. graminicola collected from major pearl millet-growing states of India. Of the 70 SZIs tested for fertility according to oospore production potential, 62 were self-sterile and 8 were self-fertile, indicating the low occurrence of homothallism in the S. graminicola populations. The sexual mating type test of the 70 SZIs, conducted by pairing each isolate with the two standard mating type tester isolates PT2 (Mat A) and PT 3 (Mat B), revealed 28 (40.0%) isolates of Mat A, 33 (47.14%) of Mat B, 8 (11.43%) of both Mat A and Mat B, and 1 (1.43%) as unknown. The frequencies of Mat A and Mat B were in approximately equal proportions among the isolates tested, except in three parental isolates. Implications of these results in understanding the dynamic genetic structure of S. graminicola population and potential for evolution of new virulence in the pathogen are discussed.