for studying the quantitative effects of flowering genes in pea. Flowering time in pea (Pisum sativum L.) is determined by genetically controlled responses to photoperiod and Key words: Temperature, photoperiod, flowering genes, temperature. To investigate these responses, 11 lines Maturity Classes, models. homozygous for the flowering genes Lf, Sn, E, and Hr were grown under contrasting semi-controlled photothermal environments and the durations (d) from Introduction sowing to first flower (f) were recorded. The effects of the four genes were quantified using a two-plane The responses of flowering times of pea (Pisum sativum photothermal model which linearly relates the rate of L.) to photoperiod (P) and temperature (T ) provide for progress from sowing to flowering (1/f ) with the mean four distinct Maturity Classes: Day-Neutral (DN ), Early pre-flowering values of temperature (T) and/or photo- Initiating ( EI ), Late (L), and Late High Response (LHR) period (P), based on 1/f=a+bT (when P is longer than (Murfet, 1971a, 1985). Six genes (Lf, Sn, E, Dne, Ppd, the critical photoperiod, P c ) and 1/f=aae+baeT+caeP and Hr) are thought to control most of the diVerences in (when P P c , which (Murfet, 1985). increased in the sequence Lf d P c ) and photothermal (PP c ) domains, delaying photoperiod, (i.e. when P is greater than the mainly by increasing a and bae, respectively. Variations critical photoperiod, P c ), by aVecting the sensitivity of in the coefficients of the thermal and photothermal the apex to the flowering signal (Murfet, 1971b; Weller responses determined that the critical photoperiod et al., 1997). varied with temperature in all photoperiod-sensitive Gene Sn is required for the photoperiodic delay of genotypes. A common base temperature of 0.2°C was flowering and is concerned with the synthesis in the leaves determined amongst Day-Neutral Class genotypes (sn) and cotyledons of an as yet unidentified graftand thermal time from sowing to flowering increased transmissible flower inhibitor (Murfet and Reid, 1973; in the sequence lf a<lf<Lf<Lf d. Intra-Class variations Weller et al., 1997). Gene Hr enhances the delaying eVect attributed to the Lf alleles were also detected in the of photoperiod on time to flowering, possibly by delaying Late (Sn hr) and Late High Response (Sn Hr) Classes. the ontogenetic decline in the production of the flowering inhibitor as the plant ages (Murfet, 1985). Gene E is