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Cross Pathogenicity of Gaeumannomyces graminis var. graminis from Bermudagrass, St. Augustinegrass, and Rice in Florida and Texas

Isolates of Gaeumannomyces graminis var. graminis were obtained from St. Augustinegrass, bermudagrass, and rice in Florida, and rice and St. Augustinegrass in Texas. In Florida, all seven isolates evaluated were cross pathogenic on each of the three grass hosts. Rice isolate FL-173 caused significantly greater disease of the lower leaf sheath and root disease severity of rice compared with other isolates, whether from rice or both turfgrass species. The rice and both turfgrass isolates generally suppressed heights and shoot and root weights compared with the control. All isolates from either rice or both turfgrass species generally had root disease ratings significantly different from the control for either bermudagrass or St. Augustinegrass. However, rice isolate FL-173 and St. Augustinegrass isolate FL-104 were significantly more aggressive on St. Augustinegrass; whereas the maximum root disease rating of bermudagrass was only associated with bermudagrass isolate FL-19 and St. Augustinegrass isolate FL-104. In Texas, both the rice isolate TX-91-1 and the St. Augustinegrass isolate TX-10466-2 of G. graminis var. graminis were pathogenic on St. Augustinegrass, common bermudagrass, and rice. Both isolates caused similar disease severity on common bermudagrass and St. Augustinegrass, but isolate TX 10466-2 caused less severe disease symptoms on rice than did isolate TX-91-1. Overall, G. graminis var. graminis was most aggressive on the host from which it was originally isolated, such as rice or St. Augustine, but differences in host-plant reactions were not always statistically significant, especially with bermudagrass.