Spread of Ergot of Sorghum (Claviceps africana) in Central Mexico

By late August 1997, sorghum ergot (Claviceps africana Frederickson, Mantle & De Milliano) had not been detected in the Bajio area in central Mexico, the second-largest sorghum (Sorghum bicolor (L.) Moench) producing area in the country, despite earlier 1997 reports of the disease in the adjacent states of San Luis Potosi, Michoacan, and Jalisco. A mid-September survey was conducted in el Bajio, primarily in the state of Guanajuato, and adjacent areas in the states of Michoacan and Jalisco. Infected sorghum heads showing ergot symptoms of honeydew and white secondary sporulation were observed in commercial grain and hybrid seed fields in all three states. Environmental conditions, late summer rains and early low temperatures promoting abundant dew, as well as extended periods of sorghum blooming, contributed to a low and delayed incidence of ergot in Guanajuato. In Michoacan and Jalisco the higher relative humidity and rainfall (around 750 ml) probably contributed to the observed epidemic of ergot. Johnsongrass (Sorghum halepense (L.) Pers.) florets also showed ergot symptoms. Macroconidia in honeydew were hyaline, oblong to oval, slightly constricted at the center, with an average size of 15 × 7 μm, agreeing with the given description of Sphacelia sorghi McRae (2), the anamorph stage of C. africana. No sclerotia were found on any host. Ergot control in this region of Mexico is being attempted by chemical means and burning of heads, even in commercial fields with minimal incidence of ergot. This report of ergot spread complements an earlier note describing the initial detection of the disease in Tamaulipas, the largest sorghum-producing state in Mexico (1). References: (1) J. Aguirre R. et al. Plant Dis. 81:831, 1997. (2) D. E. Frederickson et al. Mycol. Res. 95:1101, 1991.