Genetics of Photoperiod Sensitivity and Critical Daylength in Rice

Photoperiod sensitivity is an important breeding objective for rice ( Oryza sativa L.) grown in unfavorable environments. A study was conducted with potted plants in the screenhouse to determine the inheritance of photoperiod sensitivity and date of flowering (critical daylength). The cultivars used were: IR58, a short duration photoperiod‐insensitive cultivar; IR26760‐27, a long duration line with a slight response to photoperiod; Nam Sagui 19 (NS19), a weakly photoperiod‐sensitive cultivar; and Sac Nau (SN) and Puang Rai (PR2), strongly photoperiod‐sensitive cultivars. The regression coefficient for days to flowering on seeding date for the parents ranged from 0.07 in insensitive IR58 to −0.64 in strongly sensitive PR2. In F 2 populations, sensitivity ranged from nondominant to partially dominant, except in IR26760‐27 ✕ NS19, where sensitivity was overdominant. Two complementary, partially dominant genes conditioned photoperiod sensitivity. Highly sensitive PR2 and SN had partially dominant alleles for photoperiod sensitivity at both loci; NS19 had the partially dominant allele at the major photoperiod‐sensitivity locus (Se‐1) and IR 26760‐27 had the partially dominant allele at the locus designated Se‐3(t) . The locus Se‐3(t) conferred a short critical daylength to genotypes with Se‐1 , making them more photoperiod sensitive.