Soil salinity affects large areas of the world's cultivated land, causing significant reductions in crop yield. Despite the fact that most plants accumulate both sodium (Na+) and chloride (Cl–) ions in high concentrations in their shoot tissues when grown in saline soils, most research on salt tolerance in annual plants has focused on the toxic effects of Na+ accumulation. It has previously been suggested that Cl– toxicity may also be an important cause of growth reduction in barley plants. Here, the extent to which specific ion toxicities of Na+ and Cl– reduce the growth of barley grown in saline soils is shown under varying salinity treatments using four barley genotypes differing in their salt tolerance in solution and soil-based systems. High Na+, Cl–, and NaCl separately reduced the growth of barley, however, the reductions in growth and photosynthesis were greatest under NaCl stress and were mainly additive of the effects of Na+ and Cl– stress. The results demonstrated that Na+ and Cl– exclusion among barley genotypes are independent mechanisms and different genotypes expressed different combinations of the two mechanisms. High concentrations of Na+ reduced K+ and Ca2+ uptake and reduced photosynthesis mainly by reducing stomatal conductance. By comparison, high Cl– concentration reduced photosynthetic capacity due to non-stomatal effects: there was chlorophyll degradation, and a reduction in the actual quantum yield of PSII electron transport which was associated with both photochemical quenching and the efficiency of excitation energy capture. The results also showed that there are fundamental differences in salinity responses between soil and solution culture, and that the importance of the different mechanisms of salt damage varies according to the system under which the plants were grown.

Study of three interconnected populations identified 13 maturity QTL of which eight collocate with phenology genes, and 18 QTL for traits associated with adaptation to drought-prone environments. QTL for maturity and other adaptive traits affecting barley adaptation were mapped in a drought-prone environment. Three interconnected doubled haploid (DH) populations were developed from inter-crossing three Australian elite genotypes (Commander, Fleet and WI4304). High-density genetic maps were constructed using genotyping by sequencing and single nucleotide polymorphisms (SNP) for major phenology genes controlling photoperiod response and vernalization requirement. Field trials were conducted on the three DH populations in six environments at three sites in southern Australia and over two cropping seasons. Phenotypic evaluations were done for maturity, early vigour, normalized difference vegetation index (NDVI) and leaf chlorophyll content (SPAD), leaf waxiness and leaf rolling. Thirteen maturity QTL were identified, all with significant QTL × environment interaction with one exception. Eighteen QTL were detected for other adaptive traits across the three populations, including three QTL for leaf rolling, six for leaf waxiness, three for early vigour, four for NDVI, and two QTL for SPAD. The three interlinked populations with high-density linkage maps described in this study are a significant resource for examining the genetic basis for barley adaptation in low-to-medium rainfall Mediterranean type environments.

The usefulness of marker assisted selection (MAS) to improve diastatic power was demonstrated by selecting quantitative trait loci (QTLs) and structural gene alleles involved in enhanced diastatic power and activity of its component hydrolytic enzymes from Alexis, Amagi Nijo, Harrington, Haruna Nijo, and Sloop. Six unmapped breeders' populations involving these donor sources of malting quality were used for MAS. For each population, individual lines were pooled into classes separated on the basis of either the presence or absence of malting quality parent marker alleles at each of 9 identified loci (QTLs or structural genes). Diastatic power, β-amylase, and α-amylase activities were determined for each line, and used to compare alternative marker allele class means. Lines carrying malting parent marker alleles at a chromosome 5H locus abg463 were associated with 21–44% higher α-amylase activity levels, depending on the cross. The malting parent alleles at the chromosome 4H Bmy1 locus were associated with increased diastatic power and β-amylase activity. A simple PCR marker detecting the Bmy1 locus was found to be effective in screening for improved diastatic power, β-amylase activity, and thermostability. Lines carrying malting parent alleles at the chromosome 2H Bmy2 locus produced differences in diastatic power and β-amylase activity that, after adjusting for the correlated effect of malt protein, became non-significant. The Alexis allele of the chromosome 1H EBmac501 locus was associated with significant differences in all traits for a population carrying this source. The implication of these results to the improvement of diastatic power through MAS is discussed.

Grain weight and size are traits important to malting and feed barley. Understanding the determinants of grain weight and size, especially under stressful growing environments, will aid breeding efforts to improve these traits. The determinants of grain weight and size are discussed in relation to the pre- and post-anthesis periods of barley development. Genetic mapping of the loci influencing grain weight and size has provided a fundamental understanding of these traits, and a summary of mapped quantitative trait loci (QTLs) from Australian and international mapping populations is presented. The influence of developmental loci on grain weight and size QTLs, approaches to discovering non-developmentally related loci, and prospects for a marker assisted selection approach to improving grain weight and size are discussed.