Analysis of genetic variability in flowering habit and related genes in sorghum, Sorghum bicolor (L.) Moench

Eleven sorghum varieties, including F1 hybrids and their cross parents, were tested for the heading response at four locations using several planting times, to analyse their genetic variation. The results reconfirmed that sorghum is a short-day plant. Under a long daylength of more than 13: 02, 11 varieties were classified into the following three genotypes: A-type (Kazetachi and Tentaka): flower initiation was induced by short daylength (less than 12.5 h); B-type (MS138, MS79, Regs. Hegari and Hiromidori): flower initiation was accelerated by the exposure to a minimum temperature less than 20°C; C-type (Chohin232: 74LH3213, 3048B, Suzuho, Chohin1682: Senkin-shiro and 390B): flower initiation was neutral to the exposure to a minimum temperature and daylength. Consequently, it was assumed that a thermo-sensitivity gene (tt) and a photoperiod sensitivity gene (DD) were present and that tt displayed recessive epistasis to DD. It was suggested that the corresponding genotypes for flower initiation were: TtDd for the A-type; TTdd for the B-type; ttdd for the C-type.