Abstract : 1. Agricultural fields are commonly characterized by high nutrient and water availabilities, which are favorable for plant growth. Such conditions might promote the evolution of resource acquisitive strategies. We asked whether crop plants show root traits typical of resource acquisitive strategies and whether this strategy is primarily a result of their evolution under domestication or of the early selection of successful candidates for domestication.
2. We studied a set of 30 crop species and their wild progenitors. We set up a greenhouse experiment to measure five root traits: root thickness, root tissue density, specific root length (SRL), root mass fraction (RMF) and root length ratio. In addition, we compiled data from other wild herbaceous species, growth in similar conditions to this experiment, to place the root traits of our crops in the context of wider botanical variation.
3. Wild progenitors had thicker and less dense roots, with higher RMF and lower SRL, than other wild herbs. Thicker and less dense roots are indicative of fertile soils, which suggests that wild progenitors could have been adapted for success in agricultural conditions. Additionally, we found that domestication generally increased total plant dry mass, but none of the root traits evolved consistently towards a more resource-acquisitive strategy after domestication across all species. Root trait values differed between progenitors and crop species for most pairs surveyed, but this occurred in diverse directions depending on crop species. Such differences were independent of phylogeny, functional group or variability in the domestication processes, such as timing of the domestication event or organ under focal artificial selection.