First Report of Necrotic Ring Spot on Poa annua Putting Greens in Pennsylvania. P. J. Landschoot, Department of Agronomy, Pennsylvania State University, University Park 16802. Plant Dis. 80:712. Accepted for publication 12 April 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0712D.
Leptosphaeria korrae J. C. Walker and A. M. Sm., the causal agent of necrotic ring spot of turfgrasses (1), was isolated from Poa annua L. putting greens on three golf courses in western Pennsylvania. Disease symptoms appeared in April 1994 as circular patches of chlorotic P. annua ranging from 10 to 20 cm in diameter. Creeping bentgrass (Agrostis palustris Huds), also present in the diseased greens, was unaffected. Infected roots showed vascular discoloration and lesions were present on roots and stems. Roots and stem bases were colonized by dark brown ectotrophic mycelium. Six isolates were collected from each of the three courses and all isolates yielded pseudothecia. The pscudothecia were produced by mixing L. korrae-colonized oat grains into pots containing calcined clay, then planting wheat seeds.into the inoculum/calcined clay mixture. The pots were placed in a greenhouse and watered daily. Approximately 6 weeks after planting, mature pseudothecia were collected from the roots and stem bases of the wheat plants. Ascospores were filiform, brown, and ranged from 110 to 173 µrn in length and 4 to 6 µm wide with 5 to 9 septa. One single-ascospore isolate from each of three different pseudothecia was grown on sterile oat grains for 3 weeks. The colonized oat grains were used to inoculate pots of 4-week-old and 10-week-old P. annua. The pots were placed on a bench in a greenhouse, watered daily, and maintained at 2 cm cutting height. All three isolates were highly virulent, causing chlorosis of leaves and severe root and stem rot within 4 weeks of inoculation. Six weeks after inoculation, the majority of plants had died. Control plants were unaffected /. korrae was isolated from diseased plants. This is the first report of necrotic ring spot on P. annua putting greens in Pennsylvania.Reference: (1) J. Walker and A M. Smith. Trans. Br. Mycol. Soc 58:459, 1972.