Analysis of Photoperiod Requirements of Soft Winter Wheat.

The control of flowering time is central to reproductive success in plants, and has a major impact on grain yield. Photoperiod response genes play a major role in determining the climatic adaptation of wheat, and variation is commonly associated with Ppd-D1 locus on chromosome 2 D. A total of 76 soft winter wheat cultivars that are grown in the eastern part of the US were tested for their genotype at the Ppd-D1 locus using allele-specific markers. Flowering data were collected on fully vernalized plants grown at the phytotron under either Long Days (16 hr) or Short Days (10hr). Day/night temperatures were 20/15^oC.  The photoperiod-insensitive Ppd-D1a allele was in 35.5% of the varieties tested. The first cultivars with this allele were released after 1970. Phytotron experiments have shown that soft winter wheat cultivars differ widely in their photoperiod response from highly sensitive cultivars that flower only under long day conditions to insensitive cultivars that flower under short day conditions. All cultivars that carry Ppd-D1a allele were classified as photoperiod insensitive, indicating that this major locus plays a role in conferring photoperiod insensitivity in eastern soft winter wheats. Approximately one-third of the cultivars tested had medium to low sensitivity to photoperiod in the absence of the major Ppd-D1a allele. This suggests that the homologous photoperiod loci Ppd-B1 or Ppd-A1 may be responsible for this insensitivity.