Head smut of sorghum, sudangrass, and corn, caused bySphacelotheca reiliana(Kühn) Clint.

Abstract

Head smut, caused by the fungus Sphacelotheca reiliana (Kühn) Clint., is a disease of sorghum, sudangrass, and corn. The symptoms of the disease on these plants are described and compared. Findings of California field surveys since 1957 are reported. Varietal susceptibilities of host plants are indicated where known, with results of recent field tests, notably on the immunity of Lahoma sudangrass. Attempts to infect johnsongrass were negative. The disease is transmitted in nature by soil-borne spores, which initiate infection during pre- and postemergence growth. The incidence of infection is proportional to the amount of inoculum built up in the soil—as by continuous cropping to susceptible sorghum or by carry-over of the fungus in volunteer plants. The significance of smut mycelium in various plant tissues is considered. High and low soil temperatures are unfavorable for the infection of corn. Two distinct race groups occur in S. reiliana—one pathogenic on sorghum and one on corn. From cross-inoculation results, it is postulated that the corn race may have evolved from one of the sorghum races.