Inheritance of Avirulence in Sclerospora graminicola, the Pearl Millet Downy Mildew Pathogen

The present research studied the inheritance of avirulence by hybridizing the isolates Sg 139-4 (Mat A) a highly virulent and Sg 110-9 (Mat B) an avirulent on a pearl millet genotype IP 18292 containing a downy mildew resistance gene Rsg1. Pot-grown seedlings of IP 18292 were inoculated with sporangial inocula generated from sexual spores (oospore) of the parental isolates and their F1, F2, BC1 and BC2 progenies and incubated at 25±2°C and >90% relative humidity in a greenhouse. Downy mildew incidence was recorded two weeks after inoculation. The results indicated that avirulence was dominant over virulence and a single gene pair (AA/Aa) controlled avirulence in isolates Sg 110-9, to a corresponding resistance gene Rsg1 in IP 18292. The pattern of segregation of virulence: avirulence suggested the presence of a gene-for-gene interaction between S. graminicola and P. glaucum.