Two new Magnaporthe species pathogenic to warm-season turfgrasses in Australia.
Two new species of ectotrophic root-infecting fungi pathogenic to warm-season turfgrasses are described. Magnaporthe garrettii P. T. W. Wong & M. L. Dickinson sp. nov. causes a serious patch disease on couch (Cynodon dactylon) bowling greens in South Australia, and Magnaporthe griffinii P. T. W. Wong & A.M. Stirling sp. nov. is associated with a disease complex ("summer decline") of hybrid couch (C. dactylon × C. transvaalensis) golf greens in New South Wales and Queensland. Both are homothallic, producing perithecia readily on potato dextrose agar. They differ from other Magnaporthe spp. in having uniseriate rather than biseriate or multiseriate ascospores, and the absence of a conidial anamorph. Analysis of nuclear rRNA ITS sequences has shown that M. griffinii is a new taxon with low homology to M. grisea, M. poae, M. rhizophila, M. salvinii and Gaeumannomyces graminis. This could not be carried out with M. garrettii because there were no living cultures available and the genomic DNA extracted from dead mycelia and perithecia was totally degraded. However, the two new species can be readily distinguished by morphological differences in their perithecia and ascospores. Examination of earlier herbarium specimens has shown that M. garrettii was associated with a patch disease of buffalo grass (Stenotaphrum secundatum) in New South Wales and M. griffinii was associated with diseases of South African couch grass (C. tranvaalensis) in South Australia and of kikuyu grass (Pennisetum clandestinum) in New South Wales.