Experimental demonstration of allometric invariance of plant response to density over the course of wheat domestication.

Crop domestication and breeding have led to phenotypic changes, particularly in plant size. Allometric relationships-the link between trait and size-have been repeatedly described as invariant across taxa, suggesting strong constraints on phenotypic evolution. By analogy, artificial selection during domestication and breeding might have been strongly constrained by plant allometry, but an experimental test is lacking. We used 39 genotypes representative of the four key stages (wild, first domesticated, landrace and elite) of the evolutionary history of durum wheat. We grew them in pots as monogenotypic culture, with increasing density from 1 to 10 individuals. We measured biomass components and functional traits involved in plant competition to assess the response of genotypes to density. In response to density, wheat genotypes reduced their tiller number and flowered earlier. However, we showed invariant biomass-based responses to density across the different stages. Furthermore, allometric relationships between vegetative biomass and reproductive biomass did not vary across stages, despite phenotypic changes. Our findings contribute to strengthening empirical knowledge of the phenotypic changes in the aerial compartment over the course of plant domestication. Moreover, they reinforce the interest of using the allometric framework to better understand constraints on crop phenotype and productivity.