Mapping of QTLs for floating ability in rice

Deepwater rice (floating rice) can survive under flooded conditions because of their floating ability. We conducted genetic analysis to elucidate the genetic control of floating ability by using an F-2 and BC3F2 populations derived from a cross between deepwater and non-deepwater rice varieties. Internode elongation is the most important trait responsible for this adaptation, and is characterized by two factors: timing of the initiation of elongation and the rate of elongation. The position of the lowest elongated internode (LEI) and the rate of internode elongation (RIE) were used to measure floating ability. Two QTLs for LEI were detected on chromosomes 3 (qLEI3) and 12 (qLEI12). For RIE, two QTLs were detected on chromosomes 1 (qPJE1) and 12 (qRJE12). We confirmed the genetic effects and map positions of qLEI3, qLEI12 and qRIE12 by using BC3F2 populations. Characterization of near-isogenic lines of qLE13, qLEI12 and qRIE12 revealed that the LEI and RIE are at least partly controlled by different genetic pathways. Observation of near-isogenic lines suggested that the introgressed segment of qLEI12 and qRIE12 of chromosome 12 affected the deepwater-responsive elongation.