Photoperiodic response and heritability of the pre‐flowering interval of two red clover (<i>Trifolium pratense</i>) populations

SUMMARY The reaction to 12, 14, and 16 h photoperiods of two medium‐maturing red clover ( Trifolium pratense ) populations (cv. Kenland and Cycle 6 of a selection for long stems) under controlled environment conditions was studied. Under both 14 and 16 h photoperiods, Kenland flowered sooner and had shorter stems, more stems per plant, and greater herbage yield per plant but had a similar number of internodes compared to the long stem Cycle 6 population. A daylength between 12 and 14 h was critical for flower initiation in both populations. The critical daylength to induce stem initiation was shorter than the daylength to induce flowering in some genotypes. From half‐sib analyses, the narrow–sense heritability of the pre‐flowering interval in Kenland ranged from 15 to 23%. The expected response to one cycle of selection (5% selection intensity) for lengthening or shortening the pre‐flower interval was 2.3 to 2.4 days at the 16 h photoperiod and 3.0 days at the 14 h photoperiod. Low correlation between pre‐flowering interval, stem length, and stem number indicated that it may be possible to change one character without affecting the other two. The need for further studies of the genetic nature of the control of flowering in red clover was indicated.