SHEATH BLOTCH OF RICE - A DISEASE NEW TO THE AMERICA

Symptoms of sheath blotch were observed on rice plants grown in southern Florida. A fungus was isolated from infected tissue and identified as Pyrenochaeta oryzae. This pathogen was not previously known to occur in the Americas. Sheaths inoculated with the pathogen developed reddish brown to brown lesions within 5-15 days. P. oryzae was reisolated from inoculated tissue. Sizes of pycnidia, setae, and conidia for the isolates found in Florida and for herbarium specimens obtained from the National Fungus Collection were within the range described by other researchers. All commercial rice cultivars were susceptible to sheath blotch. This is the first decisive demonstration that P. oryzae is a pathogen of rice in the Americas.