Mating Type Distribution and Fertility Status in Magnaporthe grisea Populations from Turfgrasses in Georgia

Populations of Magnaporthe grisea associated with tall fescue and St. Augustinegrass in Georgia were analyzed for mating type distribution and fertility status in 1999 and 2000. A polymerase chain reaction based assay for mating type was developed to facilitate population analysis. M. grisea populations from St. Augustinegrass in Georgia were dominated by the Mat1-1 mating type, whereas populations from tall fescue were dominated by Mat1-2. The opposite mating type was found in low frequency (0 to 5.7%) associated with each host. The fertility status of isolates from two populations was determined using controlled crosses in vitro. Seventy-eight Mat1-1 isolates from St. Augustinegrass were sterile in test crosses, but a single Mat1-2 isolate from St. Augustinegrass was male fertile. Of 87 Mat1-2 isolates from tall fescue, 47 were male fertile in test crosses, but 19 produced perithecia that were barren. All Mat1-1 isolates from tall fescue were sterile. Although both mating types exist in M. grisea populations from turfgrasses in Georgia, no female fertile isolates were identified in sample populations. The predominance of one mating type in eight sample populations and absence of female fertile isolates in two sample populations indicates that sexual reproduction may not occur with significant frequency in M. grisea populations associated with turfgrasses in Georgia.