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SUMMARYImproving the drought resistance of high yielding rice {Oryza sativa L.) varieties for upland areas is a goal of rice breeders since upland rice relies exclusively on rainfall for water and is generally low yielding. Identifying quantitative trait loci (QTLs) which confer drought resistance promises to speed this goal. We have previously described the use of 82 restriction fragment length polymorphism (RFLP) markers in the genetic mapping of root growth characteristics that are potentially involved in drought resistance in a population of 178 Fg plants derived from a cross of two drought resistant upland varieties, Azucena and Bala. Here we report the characterization and QTL mapping of three other mechanisms of drought resistance, leaf rolling, stomatal behaviour and early flowering, in this population. When the youngest fully expanded leaf was excised from 12 rice varieties, 'IR20' and 'Bala' were identified as slow at rolling. Although 'Azucena' rolled its leaves much faster than 'Bala' upon excision, stomatal resistance rose more rapidly in 'Bala', resulting in a lower rate of water loss. By assessing leaf rolling and stomatal resistance in the Fg population, it was possible to identify QTLs for these traits. A QTL for slow leaf rolling from 'Bala' was found on chromosome 1. Two QTLs associated with resting stomatal conductance were found on chromosomes 3 and 12. QTLs for the rate of stomatal closure were found on chromosomes 3 and 7. In addition, it was possible to map QTLs associated with the days to heading which were found on chromosomes 3, 8 and 10. These results identify markers of potential value to breeders and are discussed in the context of previously reported data for heading date QTLs in rice and for stomatal conductance QTLs in maize.

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A number of accessions of the three species of diploid wheat, Triticum boeoticum, T. monococcum, and T. urartu, were grown in 50 mol m(-3) NaCl+2.5 mol m(-3) CaCl2. Sodium accumulation in the leaves was low and potassium concentrations remained high. This was not the case in T. durum grown under the same conditions, and indicates the presence in diploid wheats of the enhanced K/Na discrimination character which has previously been found in Aegilops squarrosa and hexaploid wheat. None of the accessions of diploid wheat showed poor K/Na discrimination, which suggests that if the A genome of modern tetraploid wheats was derived from a diploid Triticum species, then the enhanced K/Na discrimination character became altered after the formation of the original allopolyploid. Another possibility is that a diploid wheat that did not have the enhanced K/Na discrimination character was involved in the hybridization event which produced tetraploid wheat, and that this diploid is now extinct or has not yet been discovered.

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