Genetic dissection of cotton physiological responses to arid conditions and their inter-relationships with productivity.

Testing of the extent to which different complex traits share common genetic control provides a means to distinguish associations that are truly diagnostic of genetic potential for improved adaptation to abiotic stress, from incidental phenotypic correlations. In two generations of progeny from a cross between Gossypium hirsutum and Gossypium barbadense, quantitative trait loci (QTL) mapping was used to evaluate correspondence in genetic control of selected physiological measures and productivity under water-limited and well-watered environments, respectively. A total of 33 QTLs were detected for five physiological variables (osmotic potential (OP), carbon isotope ratio (delta13C\\; indicator of water use efficiency), canopy temperature, chlorophyll a and b), and 46 QTLs for five measures of crop productivity (dry matter, seed cotton yield (SC), harvest index, boll weight, and boll number). QTL likelihood intervals for high SC and low OP corresponded in three genomic regions,two of which mapped to homoeologous locations on the two subgenomes of tetraploid cotton. QTLs for delta13C showed only incidental association with productivity, indicating that high water use efficiency can be associated with either high or low productivity. Different cotton species have evolved different alleles related to physiological responses and productivity under water deficit, which may permit the development of genotypes that are better-adapted to and conditions.