Stroma Development, Honeydew Formation, and Conidial Production in Claviceps sorghi

The first sign of ergot (Claviceps sorghi) disease in sorghum was the appearance of superficial mycelial growth on the proximal end of the ovary 3 days after inoculation with conidial suspension. The ovary was converted into a fungal stroma 2 days later, followed by honeydew exudation from the stroma. Honeydew contained three types of conidia?macroconidia, secondary conidia, and microconidia. Macroconidia were elliptical in shape and were the first to be released in the honeydew. Under humid conditions some macroconidia on the surface of the honeydew germinated by germ tubes that enmeshed to form a hyphal mat; others germinated by erect conidiophores on which apical, pyriform secondary conidia were formed outside the honeydew surface. Small, obovate microconidia were later found in the honeydew. All three conidial forms germinated on and penetrated the stigma. Stromata developed at 14?35 C. Honeydew and conidial production occurred at 14?28 C and RH above 90% for 12?16 hr day?1. Sclerotia developed at 28?35 C and RH below 90% for 2 hr day?1. Above 90%, RH, stromata, and honeydew were colonized by saprophytic fungi and sclerotia were not forme