Research was conducted to identify and map quantitative trait loci (QTL) associated with dehydration tolerance and osmotic adjustment of rice. Osmotic adjustment capacity and lethal osmotic potential were determined for 52 recombinant inbred lines grown in a controlled environment under conditions of a slowly developed stress. The lines were from a cross between an Indica cultivar, Co39, of lowland adaptation and a Japonica cultivar, Moroberekan, a traditional upland cultivar. The QTL analysis was conducted using single marker analysis (ANOVA) and interval analysis (Mapmaker/QTL). The measurements obtained and the QTL identified were compared to root traits and leaf rolling scores measured on the same lines. One major locus was associated with osmotic adjustment. The putative locus for osmotic adjustment may be homoeologous with a single recessive gene previously identified for the same trait in wheat. The putative osmotic adjustment locus and two of the five QTL associated with dehydration tolerance were close to chromosomal regions associated with root morphology. In this population, osmotic adjustment and dehydration tolerance were negatively associated with root morphological characters associated with drought avoidance. High osmotic adjustment and dehydration tolerance were associated with Co39 alleles and extensive root systems were associated with Moroberekan alleles. To combine high osmotic adjustment with extensive root systems, the linkage between these traits will need to be broken. Alternatively, if the target environment is a lowland environment with only brief water deficit periods, selection for drought tolerance characteristics without consideration of the root system may be most appropriate.
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