Effects of a photoperiod-response gene Ppd-D1 on yield potential and drought resistance in UK winter wheat

Using a pair of near-isogenic lines (NILs) of winter wheat (Triticum aestivum L.) contrasting for the Ppd-D1 and ppd-D1 alleles, in each of Mercia and Cappelle-Desprez, experiments in two seasons (1997/8 and 1998/9) on a loamy medium sand examined differences in flowering date, resource capture, biomass production and grain yield responses to irrigation. Drought did not occur for any sustained period in unirrigated conditions in 1998 due to high seasonal rainfall. In 1999, drought developed post-flowering under unirrigated conditions. Ppd-D1 on average advanced flowering by 12 days in Mercia and 9 days in Cappelle-Desprez. Earlier flowering with Ppd-D1 was due to a shorter thermal duration from crop emergence to GS31, with no effect on the thermal duration from GS31 to GS61. In both genetic backgrounds, Ppd-D1 decreased above-ground dry matter (AGDM) at harvest in irrigated conditions by 0.3-0.9 t ha(-1) (p<0.05), but this was compensated for by increases in harvest index (HI), so that grain yield was conserved. Although Ppd-D1 decreased maximum green area index (GAI) by 0.8-1.9 this was countered by greater maintenance of green area after flowering, so that radiation interception during grain filling was conserved. The Ppd-D1 allele decreased season-long crop water uptake in the Mercia NILs in irrigated conditions by 39 mm. Effects of drought in 1999, averaging across NILs, were to decrease machine-harvested grain yield by 0.6 t ha(-1) in Mercia and by 1.8 t ha(-1) in Cappelle-Desprez (p<0.05). The Ppd-D1 and ppd-D1 NILs, though, responded similarly to drought in both genetic backgrounds. Early flowering with Ppd-D1 decreased pre-flowering water uptake under unirrigated conditions by ca. 25 mm, but increased post-flowering uptake by only 10 mm, compared to ppd-D1. This was a result of smaller season-long water uptake for Ppd-D1 compared to ppd-D1. Ppd-D1 decreased stem soluble carbohydrate measured shortly after flowering under drought by ca. 0.3 t ha(-1). Effects of Ppd-D1 on other drought-resistance traits, such as water-use efficiency (WUE; AGDM per unit crop evapotranspiration) and maximum rooting depth, appeared to be neutral. It is concluded that the effects of the Ppd-D1 allele appeared to be largely neutral on yield potential and late-season drought resistance in the UK's temperate environment in these genetic backgrounds. However, there were indications that Ppd-D1 may offer scope for breeding winter wheat cultivars with more efficient production of grain DM per unit seasonal crop evapotranspiration, associated with improved HI, compared to currently commercial UK genotypes.