Successful Crosses and Molecular Tetrad and Progeny Analyses Demonstrate Heterothallism in Mycosphaerella Graminicola

Monospore isolates of Mycosphaerella graminicola considered to originate from one ascus were analysed by the polymerase chain reaction (PCR) with 32 RAPD primers. Eighteen of these revealed three classes of polymorphisms, which enabled a RAPD-based tetrad analysis. Four pairs of isolates resulting from a single diploid nucleus were determined. A procedure to cross these isolates was developed to investigate the mating system. Three of six crosses were successful, and the segregation of mating types in accordance with the tetrad analysis strongly points to a bipolar heterothallic mating system in M. graminicola. Random ascospore progenies from the successful crosses, each comprising 54 isolates, were studied with three primers to determine the mode of inheritance of the RAPD markers. Mendelian segregation and recombination of RAPD markers was observed in all progenies.