Inter-and intracontinental sexual compatibility in Sclerospora graminicola

Oospore collections of Sclerospora graminicola , obtained from diverse locations in West Africa and India, were used to infect susceptible pearl millet plants. Asexual spores, collected from five infected plants from each collection were used as individual isolates to inoculate pearl millet seedlings, alone and in every possible combination to test for sexual compatibility type. Oospores were produced with some combinations of isolates but not others, indicating the presence of two compatibility types, designated g₁ and G₂ These were found in approximately equal proportions. There were also some isolates which produced a few oospores when inoculated alone. Tests for cross-compatibility were made by combining isolates of opposite sexual compatibility types from different collections. Not only were collections from within continents cross compatible but there was also cross-compatibility between isolates from different continents. The implications of such extensive outbreeding capacity in S. graminicola are considered.