Quantitative effects of the genes Lf, Sn, E, and Hr on time to flowering in pea (Pisum sativum L.)

Flowering time in pea (Pisum sativum L.) is determinedby genetically controlled responses to photoperiod and temperature. Toinvestigate these responses, 11 lines homozygous for the flowering genesLf, Sn, E, and Hr were grownunder contrasting semi-controlled photothermal environments and thedurations (d) from sowing to first flower (f) wererecorded. The effects of the four genes were quantified using a two-planephotothermal model which linearly relates the rate of progress from sowingto flowering (1/f) with the mean pre-flowering valuesof temperature (T) and/or photo-period (P), based on1/fa + bT(when P is longer than the critical photoperiod, Pc) and1/fa +bT + cP(when PLf alleles wason temperature sensitivity (b) when P>Pc, whichincreased in the sequenceLf^d<Lf^a. GeneHr, when together with Sn,increased photoperiod sensitivity (c) andreduced the intercept (a) when Psn determined a single plane response totemperature alone (i.e. a day-neutral response). GeneE, when present with lf Sn,increased 1/f in both the thermal (PPc) domains, mainly byincreasing a and b,respectively. Variations in the coefficients of the thermal andphotothermal responses determined that the critical photoperiod varied withtemperature in all photoperiod-sensitive genotypes. A common basetemperature of 0.2C was determined amongstDay-Neutral Class genotypes (sn) and thermal time fromsowing to flowering increased in the sequencelf^a<lf<<:f^d. Intra-Classvariations attributed to the Lf alleles were alsodetected in the Late (Sn hr) and Late High Response(Sn Hr) Classes. The linear photothermal modelprovided a sound basis for studying the quantitative effects of floweringgenes in pea.