SUCCESSFUL CROSSES AND MOLECULAR TETRAD AND PROGENY ANALYSES DEMONSTRATE HETEROTHALLISM IN MYCOSPHAERELLA-GRAMINICOLA

Monospore isolates of Mycosphaerella graminicola considered to origina te from one ascus were analysed by the polymerase chain reaction (PCR) with 32 RAPD primers. Eighteen of these revealed three classes of pol ymorphisms, which enabled a RAPD-based tetrad analysis. Four pairs of isolates resulting from a single diploid nucleus were determined. A pr ocedure to cross these isolates was developed to investigate the matin g system. Three of six crosses were successful, and the segregation of mating types in accordance with the tetrad analysis strongly points t o a bipolar heterothallic mating system in M. graminicola. Random asco spore progenies from the successful crosses, each comprising 54 isolat es, were studied with three primers to determine the mode of inheritan ce of the RAPD markers. Mendelian segregation and recombination of RAP D markers was observed in all progenies.