Past family selection in Populus nigra leads to an amplification of rust damages when neighbors are related

The competitive ability of domesticated plants, which may have conferred a fitness advantage in the wild, may result in a reduction of yield in agricultural and forestry contexts, as what matters is the group rather than the individual performance. Traits related to competitive ability can be affected by the presence or absence of related individuals in their neighborhood. Consequently, local relatedness might reveal plant-to-plant interaction that can enhance the predictive abilities of genomic models when accounted for, though it remains difficult to measure. To overcome this difficulty, we analyzed data from the French breeding program of Populus nigra L., where 1,452 genotypes were replicated six to eight times, each time encountering a different neighborhood. We assessed local relatedness and investigated genomic estimated breeding values on tree height and vulnerability to rust with a single-step GBLUP incorporating local relatedness as a covariate. The results indicate that incorporating local relatedness as an additional factor in GBLUP models has a significantly greater influence on resistance to rust than on tree height, though its overall effect on genomic predictions themselves was limited. The influence of local relatedness is small but likely trait-specific, and the genetic architecture of the trait under selection could attenuate or improve the efficacy of breeding for group performance.