Dimorphic-root ideotype demonstrates increased rice yield in nutrient-deficient paddy fields in Madagascar

Demand for rice (Oryza sativa L.) is rapidly increasing in sub-Saharan Africa; however, its productivity is constrained by nutrient-poor paddy soils, particularly those deficient in N and P. Improving root system architecture offers potential to enhance nutrient uptake efficiency and increase yield under such conditions. This study aimed to identify the most effective root phenotype for enhancing grain yield under the nutrient-deficient soil conditions in Madagascar. A high-yielding indica cultivar-IR64-and 12 near-isogenic and pyramiding lines carrying single or multiple quantitative trait loci for root growth angle, length, volume, and thickness were evaluated across several nutrient-deficient paddy fields with varying nutrient gradients with depth. A pyramiding line combining DRO1 and qsor1, which confer deeper and shallower rooting traits, respectively, exhibited significantly higher grain yield than IR64 at the yield levels of 2.7-5.1 t ha-1. This dimorphic root system expanded root distribution into both topsoil and subsoil, enhanced N and P uptake, and increased overall grain yield by 16-23% relative to IR64. These findings suggest that root system architecture expansion into multiple soil layers represents a promising ideotype for improving rice performance in nutrient-deficient paddy fields and may serve as a key breeding target to boost rice production in sub-Saharan Africa.