Transfer of deeper rooting and phosphorus uptake QTL into the popular rice variety ‘maudamani’ via marker-assisted backcross breeding

Rice suffers from drought stress due to its shallow roots, hindering water uptake from deeper soil layers. Transfer of deeper rooting QTL will modify the root architecture of the plant allowing it to extract moisture from deeper layers of the soil. Furthermore, poor soil conditions, particularly phosphorus deficiency is a common problem in the rainfed rice ecology of India which requires adequate phosphate fertilizer for obtaining higher yield. In this current investigation, two QTL (DRO1 and DRO3) for deeper rooting and one QTL for phosphorus uptake (Pup1) were introgressed into a popular variety, 'Maudamani' through marker-assisted backcross breeding. The target QTL were transferred from a pre-breed genotype, CR3996-19-9-45-1 into the popular variety. Foreground selection was performed using the tightly linked microsatellite markers in the backcross generations progenies to select plants carrying the target QTL. Background selection in each backcross generations was performed using 123 polymorphic SSR markers spread across twelve chromosomes. In each backcross generations, plants carrying all three target QTL and with highest recurrent parent genome recovery percentage was used to backcross with the popular variety, Maudamani. In BC₂F₂ generation, five plants (CR6508-111-101-129, CR6508-111-101-267, CR6508-111-101-413, CR6508-111-101-537 and CR6508-111-101-713) were selected which were homozygous for all three target QTL. The pyramided lines were evaluated for deeper rooting, low phosphorus stress tolerance and various agro-morphologic including quality traits. Progenies of those five pyramided plants showed similarity with the recipient parent for the 14 agro-morphologic and quality traits in their BC₂F₃ and BC₂F₄ generations. The introgressed lines demonstrated significantly improved root traits, including increased number of deeper roots, longer root length and higher shoot and root dry weight, compared to Maudamani under both moisture-deficit and normal conditions. Furthermore, those lines exhibited enhanced phosphorus uptake and grain yield compared to the recipient parent, Maudamani under low phosphorus conditions.