Is the relationship between grain number and spike dry weight linear? Insights from larger spikes in wheat

Abstract

Grain yield variation has been associated to variation in grain number per unit area (GN). It has been shown in the last about 40 years that GN is linearly associated to the spike dry weight (SDW) at anthesis in wheat, fact that has been useful to understand mechanistically potential grain yield. Fruiting efficiency (FE, grains per gram of spike dry weight), the slope between GN and SDW relationship, has been proposed as a possible trait to improve wheat yield potential. The linear relationship between GN and SDW implies a constant increase in GN per unit increase in spike growth and, then a constant FE. However, there are empirical and theoretical elements suggesting that this relationship would not be linear. In this study, we hypothesised and shown that the linearity of the relationship between GN and SDW would be non-linear for extreme values of SDW, implying that the FE would be noticeably reduced at these extreme cases of dry matter allocation to the juvenile spikes. These results have implications for both, genetic and man-agement improvements in grain yield.