Distribution of Mating Type Alleles and Fertility Status of Magnaporthe grisea Causing Gray Leaf Spot of Perennial Ryegrass and St. Augustinegrass Turf.

Abstract

Isolates of Magnaporthe grisea causing gray leaf spot of perennial ryegrass (PR) (Lolium perenne) and St. Augustinegrass (SA) (Stenotaphrum secundatum) were analyzed for mating compatibility and fertility. A total of 312 isolates of M. grisea from PR and 62 isolates from SA were paired with hermaphroditic tester strains from finger millet (Eleusine coracana), rice (Oryza sativa), and wheat (Triticum aestivum). All the PR isolates belonged to a single mating type, MAT1-2. Male fertility was observed in all these isolates. Asci and ascospores were not produced regardless of their developmental stage. Of the 139 (44.6%) isolates from PR that formed perithecia with the fertile tester strains, 83 (59.7%) were highly fertile, 33 (23.7%) were intermediately fertile, and 23 (16.5%) were low in fertility. Both mating types were observed among the isolates of SA, where MAT1-1 predominated the MAT1-2 type. An equal number of male and female fertile isolates were detected among these isolates obtained from a single location; however, none of the isolates behaved as hermaphrodites. Few ascospores were produced in crosses between two isolates of SA and a finger millet tester. Of the 62 monoconidial isolates of SA tested, 19 (30.6%) isolates formed perithecia, of which 5 (26.3%) were highly fertile, 7 (36.8%) were intermediately fertile, 7 (36.8%) were low in fertility, and 43 (69.4%) were infertile. The results of this study indicate that the sexual stage may not be a significant factor contributing to the genetic variation the gray leaf spot pathogen population.