QTL Mapping of Rice Root Traits at Different NH₄⁺ Levels in Hydroponic Condition

This study was initiated to identify quantitative trait loci (QTL) involved in root system development by measuring root length and weight of rice seedlings grown in hydroponic culture condition. Growth conditions for estimating the root elongation were set up to supply NH₄⁺ as a single nitrogen source. Four rice accessions and 40 introgression lines (ILs) derived from a cross between ‘Ilpumbyeo’, a temperate japonica variety, and ‘Moroberekan’, a tropical japonica accession, were used to detect QTL for two root traits of seedlings grown in 0, 250 and 500 μM NH₄⁺. Seven chromosomal regions were found to be involved in root elongation. The qRW6 QTL detected on the long-arm of chromosome 6 promoted root weight and the ‘Moroberekan’ allele at this QTL was associated with enhanced root weight at 250 μM NH₄⁺ concentration. The Moroberekan alleles were beneficial at all loci except for qRW4 at which the Ilpumbyeo allele increased root weight under 0, 250 and 500 μM NH₄⁺. A field trial was conducted for selected four ILs to know whether the introgressed Moroberekan segments harboring the beneficial QTL were associated with effects on other agronomic traits. No significant difference was detected between four ILs and Ilpumbyeo for days to heading and culm length. Two lines showed significant difference from Ilpumbyeo in spikelets per panicle and 1,000 grain weight, and the difference might be attributed to the Moroberekan segment on chromosome 6. Our QTL results indicate that the Moroberekan introgression on chromosome 6 flanked by RM162-RM3430 has the potential to enhance root traits and yield potential in the temperate japonica background.