Bread and durum wheat: intra- and inter-specific variation in grain yield and protein concentration of modern Italian cultivars

Both durum and bread wheat are well adapted to Mediterranean environments where durum wheat is traditionally assigned to more stressful conditions. Twenty-seven cultivars of each species were grown under 4 environments in Sardinia (Italy) to characterize the differences in grain yield and protein between and within them. The large number of cultivars revealed large within-species variability in yield and no or just minor between-species differences, which indicated bread wheat as better performing (6.9 vs. 6.2 t ha(-1) on average). The number of grains m(-2) (GNO) was 34% higher for bread wheat, and derived from the 26% more spikes m(2), associated with a slightly higher maximum Leaf Area Index (5.74 vs. 5.29), a higher leaf porosity and Photochemical Reflectance Index around anthesis, and higher NDVI. The high GNO of bread wheat was responsible for its lower nitrogen content (mg grain(-1)), which resulted in a lower protein percentage in spite of its lower grain weight (36 vs. 44 mg). The combination of a high GNO and low grain weight for bread wheat was particularly advantageous under favourable post-anthesis environmental conditions. The genotypic variation in yield was more dependent on grain weight than on GNO for bread wheat, whereas the opposite was true for durum wheat. These results suggest to orient breeding at increasing grain weight in bread and GNO in durum wheat. Cultivar choice seems to be more important than species choice in terms of productivity, despite the contrasting ways through which the two species generate their yield.