Photoperiodic Response of Genetically Diverse Lettuce Accessions

Abstract

A series of experiments was undertaken to study daylength-mediated control of transition to flowering in lettuce (Lactuca sativa L.), a quantitative long-day plant. Several genotypes (cultivars, landraces, and mutant lines) were grown at different photoperiods, sometimes in combination with different temperatures, and measured for number of days to either a) bolting initiation (a detectable increase in the rate of stem elongation) or b) anthesis of the first flower (a standard measure of maturity in lettuce). Experiments were conducted in controlled or partially controlled environments. Results of these studies indicate the following: a) high temperature alone is not sufficient to induce the bolting response, whereas photoperiod is; b) there is a range of genetic responses to various daylengths among lettuce genotypes; c) one of the genes known to control bolting initiation, gene Z', exhibited reverse dominance in conjunction with the Early Flowering genes, depending on the length of day. The latter observation implies the genetic role of T needs further investigation, as it does not appear to operate by simple dominance alone.