LOCATING QTL FOR OSMOTIC ADJUSTMENT AND DEHYDRATION TOLERANCE IN RICE

Research was conducted to identify and map quantitative trait loci (QT L) associated with dehydration tolerance and osmotic adjustment of ric e. Osmotic adjustment capacity and lethal osmotic potential were deter mined for 52 recombinant inbred lines grown in a controlled environmen t under conditions of a slowly developed stress. The lines were from a cross between an Indica cultivar, Co39, of lowland adaptation and a J aponica cultivar, Moroberekan, a traditional upland cultivar. The QTL analysis was conducted using single marker analysis (ANOVA) and interv al analysis (Mapmaker/QTL). The measurements obtained and the QTL iden tified were compared to root traits and leaf rolling scores measured o n the same lines. One major locus was associated with osmotic adjustme nt. The putative locus for osmotic adjustment may be homoeologous with a single recessive gene previously identified for the same trait in w heat. The putative osmotic adjustment locus and two of the five QTL as sociated with dehydration tolerance were close to chromosomal regions associated with root morphology, In this population, osmotic adjustmen t and dehydration tolerance were negatively associated with root morph ological characters associated with drought avoidance. High osmotic ad justment and dehydration tolerance were associated with Co39 alleles a nd extensive root systems were associated with Moroberekan alleles. To combine high osmotic adjustment with extensive root systems, the link age between these traits will need to be broken. Alternatively, if the target environment is a lowland environment with only brief water def icit periods, selection for drought tolerance characteristics without consideration of the root system may be most appropriate.