Previous work identified the wild barley (Hordeum vulgare ssp. spontaneum) accession CPI-71284-48 as being capable of limiting sodium (Na(+)) accumulation in the shoots under saline hydroponic growth conditions. Quantitative trait locus (QTL) analysis using a cross between CPI-71284-48 and a selection of the cultivated barley (H. vulgare ssp. vulgare) cultivar Barque (Barque-73, a moderate Na(+) excluder) attributed the control of the Na(+) exclusion trait from CPI-71284-48 to a single locus on the short arm of chromosome 7H, which was named HvNax3. The locus reduced shoot Na(+) accumulation by 10-25% in plants grown in 150 mM NaCl. Markers generated using colinearity with rice and Brachypodium, together with the analysis of introgression lines and F(2) and F(3) families, enabled HvNax3 to be mapped to a 1.3-cM interval. Genes from the corresponding rice and Brachypodium intervals encode 16 different classes of proteins and include several plausible candidates for HvNax3. The potential of HvNax3 to provide a useful trait contributing to salinity tolerance in cultivated barley is discussed.

SummaryDrought tolerance of the wheat cultivar Bobwhite was previously enhanced by transformation with a construct containing the wheat DREB3 gene driven by the stress-inducible maize Rab17 promoter. Progeny of a single T 2 transgenic line were used as pollinators in crosses with four elite bread wheat cultivars from Western Australia: Bonnie Rock, IGW-2971, Magenta and Wyalkatchem, with the aim of evaluating transgene performance in different genetic backgrounds. The selected pollinator line, BW8-9-10-3, contained multiple transgene copies, had significantly improved drought tolerance compared with wild-type plants and showed no growth and development penalties or abnormalities. A single hybrid plant was selected from each cross-combination for three rounds of backcrossing with the corresponding maternal wheat cultivar. The transgene was detected in all four F 1 BC 3 combinations, but stress-inducible transgene expression was found in only three of the four combinations. Under well-watered conditions, the phenotypes and grain yield components of the F 2 BC 3 transgene-expressing lines were similar to those of corresponding recurrent parents and null-segregants. Under severe drought conditions, the backcross lines demonstrated 12-18% higher survival rates than the corresponding control plants. Two from four F 3 BC 3 transgenic lines showed significantly higher yield (18.9% and 21.5%) than control plants under limited water conditions. There was no induction of transgene expression under cold stress, and therefore, no improvement of frost tolerance observed in the progenies of drought-tolerant F 3 BC 3 lines.

A wide range of variability in both Na + exclusion and salinity tolerance was shown in Triticum dicoccoides and the best performing genotype, from Getit, was identified for further study and for crossing. In bread wheat, plants BC 6 F 1 from the cross Chinese Spring/line SQ1 showed less variability, but the line 1868 was identified as a potential source of tissue tolerance to salinity. Two Afghani durum landraces were identified among 179 screened, with approximately 50% lower Na + accumulation in shoots. Genetic analysis of F 2 progenies between landraces and durum wheat showed clear segregation indicating on the single, major salinity tolerance gene in the landraces. Further genetic and molecular analysis of the candidate gene and its localization is in the progress. QTL analysis of two non-pedigree related mapping populations of bread wheat, Cranbrook × Halberd and Excalibur × Kukri, showed one QTL in each population on the same region of chromosome 7AS, independent of year or growing conditions (both supported hydroponics and field trials), and a novel gene is expected to be associated with this QTL.