Quantitative trait loci for root-penetration ability and root thickness inrice: Comparison of genetic backgrounds

Drought is the major abiotic stress limiting rice (Oryza sativa) production and yield stability in rainfed lowland and upland ecosystems. Root systems play an important role in drought resistance. Incorporation of root select ion criteria in drought resistance improvement is difficult due to lack of reliable and efficient screening techniques. Using a wax-petrolatum layer s ystem simulated to compacted soil layers, root traits were evaluated in a d oubled haploid (DH) population derived from the cross between 'IR64' and 'A zucena'. Twelve putative QTLs (quantitative trait loci) were detected by in terval mapping comprising four QTLs for root-penetration ability, four QTLs for root thickness, two QTLs for penetrated root number, and two QTLs for total root number. These QTLs individually explained 8.4% to 16.4% of the p henotypic variation. No QTL was detected for maximum penetrated root length by interval mapping. One QTL located between RG104 and RG348 was found to influence both root-penetration ability and root thickness. QTLs for root-p enetration ability and root thickness were compared across two populations, 'IR64'-'Azucena' and 'CO39'-'Moroberekan', and different testing condition s. The identified consistent QTLs could be used for marker-assisted selecti on for deep and thick roots with high root-penetration ability in rice.