Abstract
A Single sorghum selection, I. S. 2663, of Sorghum bicolor [Sorghum bicolor (L.) Moench] was found to have both midge [Contarinia sorghicola (Coq.)] and anthracnose head blight [Colletotrichum graminicolum (Ces.) Wils.] Resistance while a second selection, I. S. 2660, from the Indian-Rockefeller Sorghum Collection was resistant to midge in Hawaii. Laboratory induced midge infestations and anthracnose inoculations of the sorghum inflorescence at anthesis indicate that this character is likely to be an exclusion mechanism that confer resistance to both organisms. Glumes of spikelets of I.S. 2660 and I. S. 2663 remained closed throughout anthesis while glumes of susceptible control, B-Line 6202 and R-Line C20014, remained open during anthesis. Foliage resistance to anthracnose may also have led to improved head blight resistance. Resistance to infection of the testa by C. graminicolum was found to be associated with pigmentation of the pericarp. A fourth factor Associated with anthracnose and insect resistance was panicle structure. Moisture and insects accumulated more readily in the compact panicle as compared to the loo e panicle and thus predisposed spikelets to fungal infections and insects during periods of wet·, rainy weather. Plants of the F1 generation from a cross between a cytoplasmic sterile selection and I.S. 2660 did not express the closed-glume character at anthesis suggesting that this character is recessive, incompletely dominant or regulated by cytoplasmic factors
