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 cultures, with
increasing density from one to ten 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 tillers 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 in
using the allometric framework to better understand constraints on crop
phenotype and productivity.