Effect of allele combinations at loci on durum wheat grain filling at contrasting latitudes.

Flowering time is the most critical developmental stage in wheat, as it determines environmental conditions during grain filling. Thirty-five spring durum genotypes carrying all known allele variants at loci were evaluated in fully irrigated field experiments for three years at latitudes of 41°N (Spain), 27°N (northern Mexico) and 19°N (southern Mexico). Relationships between weight of central grains of main spikes () and thermal time from flowering to maturity were described by a logistic equation. Differences in flowering time between the allele combination causing the earliest (GS100/) and the latest () flowering were 7, 20 and 18 days in Spain, northern Mexico and southern Mexico, respectively. Flowering delay drastically reduced the mean grain filling rate () and at all sites. At autumn-sowing sites, an increase of 1°C in mean temperature during the first half of the grain filling period decreased by 5.2 mg per grain. At these sites, was strongly dependent on . At the spring-sowing site (southern Mexico), depended on both and grain filling duration. Our results suggest that incorporating the allele combinations GS100/ and GS105/ (alleles conferring photoperiod insensitivity) in newly released varieties can reduce the negative effects of climate change on grain filling at the studied latitudes.