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 determined by genetically contr olled responses to photoperiod and temperature. To investigate these respon ses, 11 lines homozygous for the flowering genes Lf, Sn, E, and Hr were gro wn under contrasting semi-controlled photothermal environments and the dura tions (d) from sowing to first flower (f) were recorded. The effects of the four genes were quantified using a two-plane photothermal model which line arly relates the rate of progress from sowing to flowering (1/f) with the m ean pre-flowering values of temperature (T) and/or photoperiod (P), based o n 1/f=a+bT (when P is longer than the critical photoperiod, P,) and 1/f=a'b'T+c'P (when P<P-c). The main effect of Lf alleles was on temperature sens itivity (b) when P > P-c, which increased in the sequence Lf(d)<Lf<lf<lf(a) . Gene Hr, when together with Sn, increased photoperiod sensitivity (c') an d reduced the intercept (a') when P<P-c. Allele sn determined a single plan e response to temperature alone (i.e. a day-neutral response), Gene E, when present with If Sn, increased 1/f in both the thermal (P>P-c) and photothe rmal (P less than or equal to P-c) domains, mainly by increasing a and b', respectively. Variations in the coefficients of the thermal and phototherma l responses determined that the critical photoperiod varied with temperatur e in all photoperiod-sensitive genotypes. A common base temperature of 0.2 degrees C was determined amongst Day-Neutral Class genotypes (sn) and therm al time from sowing to flowering increased in the sequence If(a) < If <Lf < Lf(d). lntra-Class variations attributed to the Lf alleles were also detec ted in the Late (Sn hr) and Late High Response (Sn Hr) Classes. The linear photothermal model provided a sound basis for studying the quantitative eff ects of flowering genes in pea.