Flowering in Pisum. Hr, a gene for high response to photoperiod

Abstract

LHR (late high response) peas are similar to L (late) peas under long days but their flowering node is delayed to a much larger extent by short days. The LHR phenotype is conferred by dominant Hr in combination with Sn. Addition of E returns flower initiation to the early region (phenotype EI—early initiating). Since Lf is epistatic to E, genotype Lf E Sn Hr is also expected to be LHR. Hr has little effect by itself and lf e sn Hr is essentially ED (early developing) with some EI tendencies. Hr is in linkage group III 3 map units from the seed marbling gene M. Hr plants sometimes misclassify; lf e Sn Hr as EI and lf e sn Hr as L. Cool temperatures reduce eeffect of Hr but above 15° lf e Sn Hr plants approach an obligate long day requirement for flowering. They can flower in response to a single inductive cycle. The flower inhibiting effect of Sn, which short days favour, diminishes with age. It is suggested that Hr blocks the aging effect.