Differences in time to heading that remain after photoperiod and vernalisation requirements have been saturated are classified as earliness per se ( Eps ) effects. It has been commonly assumed that Eps genes are purely constitutive and independent of environment, although the likely effect of temperature on Eps effects in hexaploid wheat has never been tested. We grew four near isogenic lines (NILs) for the Eps gene located in chromosome 1D ( Eps-D1 ) at 6, 9, 12, 15, 18, 21 and 24 °C. In line with expectations we found that lines carrying the Eps -late allele were always later than those with Eps -early alleles. But in addition, we reported for the first time that the magnitude of the effect increased with decreasing temperature: an Eps x temperature interaction in hexaploid wheat. Variation in heading time due to Eps x temperature was associated with an increase in sensitivity to temperature mainly during late reproductive phase. Moreover, we showed that Eps alleles exhibited differences in cardinal (base, optimum, maximum) temperatures and that the expression of ELF3 , (the likely candidate for Eps-D1 ) also interacted with temperature.

Ppd-1a reduced the number of fertile florets due largely to lowering floret survival, and the effect was not proportional to the duration of the late reproductive phase.

Wheat Ppd-1a alleles did not affect leaf initiation but accelerated spikelet initiation, which partially compensated for the reduction in spikelet number due to a shorter period of spikelet initiation.

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