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First report in the Americas of sorghum ergot disease, caused by a pathogen diagnosed as claviceps africana

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Hassan, H.A.G.; Mantle, P.G.; Reis, E.M.

A widespread and economically important epidemic of sugary disease in irrigated production of F1, hybrid seed of Sorghum bicolor (L.) Moench occurred for the first time, and of unknown origin, in Brazil in mid-1995 in the states of Sao Paulo, Minas Gerais, and Goias. Since we know at least three distinct ergot fungi that are sorghum pathqgens in Africa, India or Japan, diseased male-sterile (ms) sorghum florets from Ribeirao Preto, Sao Paulo, bearing dried honeydew were used as a source of inoculum for ms sorghum in England in October. Within 7 days after inoculation, glumes of infected florets were forced apart by a sphacelial mass that had replaced the ovary. High humidity enabled copious exudation of honeydew containing macrospores and microspores typical of Sphacelia sorghi McRae. Within 1 to 2 days after exudation, the honeydew bore a white surface fructification of potentially airborne secondary spores that arose directly by iterative germination of macrospores near the honeydew surface. This is a characteristic of the African ergot pathogen Claviceps africana Frederickson, Mantle and de Milliano (1). In addition, analysis of honeydew revealed one dominant saccharide, shown by mass spectrometry to contain three hexoses, transformed from sucrose as is typical of C. africana. Analysis of 100 pseudosclerotia (350 mg) revealed the alkaloids dihydroergosine and festuclavine that together are diagnostic of C. africana, a feature that similarly identified this African pathogen in Japan (2), where its recognition was in addition to that of another sorghum ergot pathogen.