Genetic control of a photoperiod-sensitive response in Sorghum bicolor (L.) Moench

Photoperiod-sensitive (PS) sorghums (Sorghum bicolor L. Moench) are not unc ommon, 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 cros sed as females with EBA-3 by hand emasculation and pollination. F-1 and F-2 populations were evaluated for photoperiod response as indicated by flower ing 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 segregati on data. Nine of ten F-1 progeny were strongly PS. Plants in nine F-2 popul ations segregated for photoperiod response. Segregation in eight of the F-2 populations fit a 9:7 PS/PI ratio, indicating that two independent gene lo ci were interacting in complementary dominant epistasis. Evaluation of cros ses between EBA-3 and maturity standards for the Ma(1), Ma(2), Ma(3), and M a(4) loci indicated that the loci responsible for this photoperiod sensitiv ity are different from previously characterized loci. The gene symbols prop osed for these two loci are Ma(5) and Ma(6).