GROWTH AND PATHOGENICITY OF LEPTOSPHAERIA-KORRAE IN BERMUDAGRASS

Maryland isolates of Leptosphaeria korrae from bermudagrass (Cynodon dactylon ''Tufcote'') affected with spring dead spot (SDS) were compared with a New York and a Rhode Island isolate of L. korrae from Kentucky bluegrass (Poa pratensis). Pseudothecia produced on inoculated bermudagrass roots were identical and contained ascospores of similar length (mean range, 168-189 .mu.m) for all three isolates, confirming a common identity. The three isolates grew similarly at temperatures ranging from 15 to 30 C, with most rapid growth occurring at 25 C. Tufcote bermudagrass plants inoculated with a Maryland isolates were severely damaged at 15 C. Mortality at 20 C was 44%, but at 25 and 30 C, no disease symptoms were visible. The fungus was reisolated from diseased or necrotic plants. Greenhouse studies revealed significant differences in isolate virulence and susceptibility of bermudagrass cultivars to disease. The greenhouse inoculation methods employed, however, did not provide a reliable means for assessing susceptibility to L. korrae. Isolation of L. korrae from SDS-affected bermudagrass in Maryland and subsequent pathogenicity tests provide documentation that this fungus is an incitant of SDS in the eastern United States.