Mapping quantitative trait loci associated with root growth in upland rice (Oryza sativa L.) exposed to soil water-deficit in fields with contrasting soil properties

A mapping population of 114 lines from Bala × Azucena was grown under drought stress at two field sites with contrasting soil physical properties. Drought was imposed between 35 and 65 days after sowing (DAS) and root density at 35 cm depth was measured 70 DAS. Leaf rolling, leaf drying and relative water content were recorded as indicators of drought avoidance. Root density correlated with indicators of drought avoidance. Two significant and two putative quantitative trait loci (QTLs) for root density and 28 QTLs for drought avoidance were identified. Most QTLs did not agree between sites. There was also reasonable agreement between leaf-drying QTLs and previously reported root-growth QTLs detected under controlled conditions (in contrast to a previous screen on soil with a higher penetration resistance). These data also reveal QTL × environment interaction, which will need to be understood more clearly if progress towards breeding for drought resistance via alterations of root morphology is to be achieved.