Timing of photoperiod sensitivity in relation to floral initiation in contrasting genotypes of pea (Pisum sativum L.)

Flowering genes are main determinants of specific responses of pea genotypes to photoperiod and temperature, and hence determine maturity classes. However, it is unclear when and for how long plants are photoperiod-sensitive during pre-flowering development and how flowering genes affect these phases. To evaluate this, a reciprocal transfers experiment (at 18.5 °C mean temperature) between long and short days and vice versa (20 and 11.5 h d−1) was conducted with nine genotypes of pea with different allele combinations of the four major flowering genes Lf, E, Sn and Hr, which covered the whole range of maturity classes. Results showed that pre-flowering development in pea has three successive phases regarding photoperiod sensitivity: a pre-sensitive (a1), a photoperiod-sensitive (I) and a post-sensitive phase (a3). Flowering genes had their greatest effects on the duration of the sensitive phase I. In the absence of allele Sn there was no photoperiod-sensitive phase. Allele E, under the appropriate background for expression, delayed and reduced the duration of the photoperiod-sensitive phase, while allele Hr delayed the onset of the photoperiod-sensitive phase and increased its length, especially under short days. Gene Lf with four alleles had a modifying effect on the length of the sensitive phase. Floral initiation occurred either before or during the photoperiod-sensitive phase, therefore in all photoperiod-sensitive genotypes the rate of development during the early stages of flower development was influenced by daylength. Lf and Sn were the main flowering genes influencing time of floral initiation.