Yield determination, interplay between major components and yield stability in a traditional and a contemporary wheat across a wide range of environments

Physiological bases of Mediterranean wheat yield improvements have been less explored than in other regions, particularly so during the period following the Green Revolution. Due to the common terminal stress of Mediterranean regions, it could be hypothesized that contemporary cultivars would exhibit improved average grain weight and yield stability compared with a traditional cultivar. Despite the lack of clear evidence in the literature, farmers in Mediterranean regions may prefer growing traditional cultivars over modern ones under the poorest environments and allocate the best lands to more contemporary cultivars. For instance, in our region this has been the case with Anza (a traditional, but semi-dwarf, cultivar) and Soissons (more modern and with a putatively higher potential yield than Anza). We analysed in detail for these two cultivars yield determination and its responsiveness to a very wide range of growing conditions (across six experiments, yield ranging from less than 1 to more than 8 Mg ha−1). Both cultivars responded to the improved yielding conditions noticeably but Soissons did so more strongly, revealing a clearly higher yield potential. The higher yield stability of the traditional cultivar did not imply consistently better performance under the lowest yielding conditions. The main component explaining the yield advantage of the contemporary cultivar was the number of grains per m2 though the traditional cultivar exhibited a sort of partial compensation due to possessing a consistently higher average grain weight. Across all conditions, the overall fruiting efficiency of the contemporary cultivar (111.4 ± 7.5 grains gspike−1) was significantly higher than that of the traditional one (88.3 ± 3.9 grains gspike−1), which was the basis of a higher spike fertility in the contemporary than in the traditional cultivar, observed in most of the spikelets consistently across environmental conditions with a clear trend to increase the number of spikelets exhibiting a significant difference in fertility between the two cultivars and the overall difference in spike fertility between them. Analysing in detail the weight of each individual grain in the last two experiments, we showed that the improved spike fertility due to a higher fruiting efficiency did not bring about reductions in grain weight potential and the dominant cause of the partial compensation was the increase in the proportion of grains in distal positions (constitutively smaller than proximal grains) in the contemporary cultivar.