Assessing the Ability of Durum Wheat-Thinopyrum ponticum Recombinant Lines to Suppress Naturally Occurring Weeds under Different Sowing Densities

The use of synthetic chemicals in cropping systems is becoming more controversial and highly debated worldwide, owing to its impacts on the environment, food safety, and human health. For this reason, sustainable crop management strategies are gaining increasing interest. In this perspective, agronomic practices and use of disease-resistant and competitive genotypes represent valuable tools in the hands of farmers. The competitive ability of two durum wheat-Thinopyrum ponticum recombinant lines (named R5 and R112), carrying effective resistance genes towards main rust diseases and enhanced yield-related traits in their alien chromosome segments, was investigated in comparison with that of a widely grown commercial cultivar (Tirex), under two sowing densities (250 and 350 seeds m−2), in the presence or absence of weeds. Yield-related traits and specific attributes that confer competitive ability were recorded in two subsequent seasons. R5 was the most weed-suppressive genotype, whereas Tirex was the least competitive. R112 was the best yield performer under favorable weather conditions (5.6 t ha−1), while it suffered the presence of weeds in the drier year (−38% grain yield). Although 350 seeds m−2 appeared to be the most effective sowing density for suppression of weeds (−16% weed biomass), adoption of the lower density can optimize grain yield and limit weed infestation in dry seasons. A suitable combination of sowing density and genotype choice can improve yield performance. R112 required the higher sowing rate to maximize grain yield (+43% as compared to the lower sowing rate), while R5 proved to be a density-neutral genotype.