Flowering in Pisum: multiple alleles at the lf locus

Abstract

Two further alleles lfa and Lfd are proposed for the flowering gene Lf. The dominance order is Lfd>Lf>lf>lfa, with ability to delay flowering descending in that order. Homozygous lfa plants can flower as early as node 5 or 6 but generalised statements regarding the flowering node for these alleles are avoided since the position depends on the status of the other major flowering loci, the background for various quantitative systems and the environmental conditions. In the present crosses heterozygotes of lfa with the other alleles were always distinguishable from the lfa homozygotes and segregation was therefore distinct even in long days. Parental lines 60 (lf E Sn hr) and 7 (lfa E Sn hr) flowered less than four nodes apart but dominance of If over lfa was 0·69 and strong canalisation of development in this early region allowed classic Mendelian analysis of the data. A relatively strong polygenic system contributed to within-class variation of lfa and lf plants. The degree of dominance of Lf over lfa varied with the photoperiod and the background of internode-length genes. Lfd Lf heterozygotes were not clearly distinguishable from either homozygote. The results of graft studies are in agreement with the proposal that the Lf alleles determine sensitivity of the apex to the flowering hormones. Type lines are appointed for the four alleles.