Inheritance of Reaction of Sorghum bicolor (L.) Moench to Toxin Produced by Periconia circinata (Mang.) Sacc.¹

The inheritance was determined for the reaction of Sorghum bicolor (L.) Moench to the toxin produced by the saprophyte, Periconia circinata (Mang.) Sacc. (1) A precise laboratory screening technique was developed whereby seedlings were subjected to the toxin devoid of the P. circinata organism. (2) The inheritance of the host‐pathogen reaction among established cultivars was confirmed to be controlled at a single locus. Susceptible seedlings ( PcPc ) died quickly, resistant seedlings ( pcpc ) grew normally, and heterozygotes (Pcpc) showed an intermediate response. (3) The mutation frequency from susceptibility to resistance ( Pc → pc ) was one per 7,876 gametes among 55,137 seedlings of ‘Colby,’ a susceptible cultivar. Mutations at the controlling locus are sufficiently frequent to be of significance in a breeding program and the disease response is precise enough for critical genetic analyses.