Relationships between grain-filling parameters, fertility, earliness and grain protein of durum wheat in a Mediterranean environment

Seven Italian durum wheat (Triticum turgidum L. var. durum) cultivars characterized by different height, time to anthesis, fertility and kernel weight were compared under different moisture levels and soil types in two experiments. Duration, and maximum and average rate of grain-filling (GF) were estimated from 2nd and 3rd order polynomials, regressing kernel weight on growing degree days (GDD, base temperature 9 degrees C) In both experiments Messapia was the earliest cv, flowering between 132 and 139 days after sowing (das), and Vespro and Creso the latest, flowering between 141 and 148 das. The largest kernels, ranging between 51.8 and 59.5 mg, were always realized by these three cultivars and were always associated with the highest rates of GF. Average rates ranged from 105 to 152 mu g degrees C day(-1) and were significantly correlated, both environmentally and phenotypically, with maximum kernel weight. Maximum rates of GF, ranging from 172 mu g degrees C day(-1) in the genotype D3415 to 282 mu g degrees C day(-1) in cv Creso, were only phenotypically correlated with maximum kernel weight. GF duration was related to earliness as it ranged from a minimum of 380 GDD in the late cv Vespro, to a maximum of 481 GDD in the earliest cv Messapia. Fertility varied greatly, from 37 kernels per spike in Creso and Vespro, to 61 kernels per spike in Vespro. Significant differences in grain protein were recorded between cultivars (8.9% in Karel to 15.8% in D3415) and soils (10.8% and 14.1%). In this environment, large kernels can be achieved with genotypes characterized by high rates of GF, irrespective of earliness, and without negative effects on spike fertility and on grain protein content.