FIRST REPORT OF SOUTHERN BLIGHT OF COMMON BARLEY IN PUERTO-RICO

In 1990-91, 96% of the test plants in a barley (Hordeum vulgare L.) wi nter nursery in Puerto Rico was lost to Sclerotium rolfsii. Small necr otic lesions (1-3 mm long) developed at the base of the stem, followed by wilting and general chlorosis as the lesions progressed and eventu ally girdled the base of the stem. Sclerotia then developed on the pla nts at the stem base. Two morphologically different strains of S, rolf sii that were mycelial incompatible were isolated. This is the first r eport of a destructive blight due to S. rolfsii on field barley in the Caribbean. The apparent rate of disease increase (r) was estimated to be 12.2% per day using the logistic model, with an initial disease in cidence of 0.042% (R(2) = 0.89, p less than or equal to 0.001).