Genetic Control of a Photoperiod‐Sensitive Response in Sorghum bicolor (L.) Moench

Photoperiod‐sensitive (PS) sorghums ( Sorghum bicolor L. Moench) are not uncommon, but the production of a PS hybrid from two photoperiod insensitive (PI) lines is unusual. The inbred line EBA‐3 is PI, but F 1 hybrids of EBA‐3 with most other PI inbreds are PS and will not initiate floral development until daylengths are <12 h and 20 min. The objective of this study was to determine the inheritance of the PS response. Ten PI inbred lines were crossed as females with EBA‐3 by hand emasculation and pollination. F 1 and F 2 populations were evaluated for photoperiod response as indicated by flowering date in plantings at College Station and Halfway, TX. F 2:3 progeny for two of the crosses plus two testcrosses were used to confirm F 2 segregation data. Nine of ten F 1 progeny were strongly PS. Plants in nine F 2 populations segregated for photoperiod response. Segregation in eight of the F 2 populations fit a 9:7 PS/PI ratio, indicating that two independent gene loci were interacting in complementary dominant epistasis. Evaluation of crosses between EBA‐3 and maturity standards for the Ma 1 , Ma 2 , Ma 3 , and Ma 4 loci indicated that the loci responsible for this photoperiod sensitivity are different from previously characterized loci. The gene symbols proposed for these two loci are Ma 5 and Ma 6 .