As soil resources worldwide are depleting, while the demand for food promises to continue to grow, there is a pressing need to produce more from less input.  One important factor influencing stand- and community-level plant performance are plant-plant interactions under resource limitation. Plants compete for sunlight above ground by increasing leaf area and stem height. Belowground, competition mechanisms include increasing root biomass and reducing the size or changing the direction of competitors' root systems. While competition can benefit individuals, it may lead to negative outcomes at the stand level. Hence, understanding the developmental and physiological response to competition and its underlying genetic basis might enable the rational design of plantings and breeding for higher performance in agriculture. Sorghum plants from 10 traditional local varieties were grown with and without plants of a common competitor genotype, under well-watered and drought conditions in pots. Competitor stems were forced to grow sideways to prevent shading. Our results show that competition acts as biotic stress, limiting relative and absolute growth rates starting from 10 days after sowing and leaf area at 35 days after sowing. The presence of competitors under well-watered conditions had a comparable effect to drought without competitors. The genetic variance was observed between landraces, with some responding more severely to competition than drought. In addition, we demonstrate the relationship between the root system architecture of different landraces and their competition response. Our study reveals how early below-ground competition affects subsequent above-ground development. In this research’s next step, we plan to use the lines reported here to identify the genetic basis of competition response.