Inheritance of a thermo-sensitivity gene controlling flower initiation in sorghum

The existence of a sorghum (Sorghum bicolor Moench) thermo-sensitivity gene has been proposed to account for the acceleration of flower initiation when plants are exposed to a temperature lower than 20°C. Four varieties and their F1, F2, F3 and BC1F1 populations were evaluated for days to emergence of flag leaf (DEFL) under the field condition of a long daylength (> 13 h) and temperatures over 20°C for at least 40 days after sowing. The F1 hybrids, Hiromidori (Norin Ko-2) : 390 (early) × Regs.Hegari (late) and Natsuibuki (Norin Ko-9) : MS175 (late) × Daikoukaku (early), showed the same flowering response as Regs.Hegari and MS175 which show a delay in DEFL under temperatures over 20°C, suggesting the presence of a dominant thermo-sensitivity gene. In two different F2 populations, the segregation of early and late plants for DEFL fitted in with the expected ratio of 1 : 3, indicating that a single dominant gene was controlling the phenotype. The inheritance mode was confirmed in two different BC1F1 populations, where the expected ratio of 1 : 1 (early : late) was observed in the segregation of BC1F 1 of 390 × F1 and F1 × Daikoukaku. As expected, no segregation was observed in BC1F1 populations of F1 × Regs.Hegari and MS175 × F1. These results suggest that the sorghum thermo-sensitivity for flower initiation is controlled by a monogenic dominant gene of late over early, and the symbol TT is assigned to the genotype in which flower initiation is accelerated by the exposure to a temperature lower than 20°C.