A major QTL controlling deep rooting on rice chromosome 4

Drought is the most serious abiotic stress that hinders rice production under rainfed conditions. Breeding for deep rooting is a promising strategy to improve the root system architecture in shallow-rooting rice cultivars to avoid drought stress. We analysed the quantitative trait loci ( QTLs) for the ratio of deep rooting ( RDR) in three F-2 mapping populations derived from crosses between each of three shallow- rooting varieties (`ARC5955', `Pinulupot1', and `Tupa729') and a deep- rooting variety, `Kinandang Patong'. In total, we detected five RDR QTLs on chromosomes 2, 4, and 6. In all three populations, QTLs on chromosome 4 were found to be located at similar positions; they explained from 32.0% to 56.6% of the total RDR phenotypic variance. This suggests that one or more key genetic factors controlling the root growth angle in rice is located in this region of chromosome 4.