Flowering and branching in Lathyrus odoratus L.: loci sp and b.

A second flowering gene, Sp, which influences sensitivity to photoperiod, is identified in the sweet pea, Lathyrus odoratus L. Genes Sp and Dn (h) act in a complementary manner to confer the summer-flowering phenotype and a near obligate long day requirement for flowering in the unvernalized state. Mutations sp and Dn (i) each diminish the response to photoperiod, and genotypes sp Dn (h) and Sp Dn (i) confer a spring-flowering phenotype. Response to photoperiod is further reduced in genotype sp Dn (i), which flowers only marginally later than the day-neutral or winter-flowering phenotype characterized by genotypes Sp dn and sp dn (gene dn is epistatic to the gene pair Sp/sp). Like Dn (i), gene sp reduces basal branching, while a branching gene, here resymbolized b, is shown to delay flowering in certain circumstances. Gene dn largely prevents basal branching in either b or B plants, but dn b plants do produce lateral shoots from the upper nodes, leading to a novel phenotype. The implications of the interactions between genes sp, Dn (i), dn and b are discussed with respect to the control of flowering and branching.