Earliness per se effects on developmental traits in hexaploid wheat grown under field conditions

Earliness per se (Eps) genes are critical for fine-tuning flowering time and likely to modify other developmental traits as well. Effects of Eps alleles on components comprising flowering time of hexaploid wheat have not been studied. In this work, we evaluated under field conditions the effects of Eps alleles on flowering time and on a number of developmental traits using four groups of near isogenic lines (NILs) with contrasting Eps alleles (late vs early alleles). The NIL groups were derived from the Avalon x Cadenza (AxC) cross with the Eps effects on either chromosome 1D or 3A and from the Spark x Rialto (SxR) cross with the Eps effect on chromosome 1D. Eps-D1-late alleles delayed flowering (and the effect was stronger in AxC than in SxR); while Eps 3A did not have any effect. Differences in flowering time between NILs with Eps-D1-early and -late alleles were mainly associated with the effects of this gene on the duration of the late reproductive phase consistently for both crosses. However, the effects of Eps-D1 on other developmental traits were different depending on the specific cross used to produce the NILs. The Eps-D1-early allele from AxC did not affect FLN, reduced spikelet initiation phase and, in turn, decreased the spikelet number (though less than proportionally as it accelerated the rate of spikelet initiation as well), whilst Eps-D1-early allele from SxR affected marginally FLN, but had no effects on either spikelet initiation phase or spikelet number. The results reported from this study in Mediterranean conditions conflict quantitatively (Eps-D1) or qualitatively (Eps 3A) with results observed previously in the UK, likely evidencing the existence of Eps x temperature interactions.