Drought, being a yield-limiting factor, has become a major threat to international food security. It is a complex process, and drought tolerance response is carried out by various genes, transcription factors, microRNAs, hormones, proteins, co-factors, ions and metabolites. This complexity has limited the development of crop cultivars for drought tolerance. Breeding for drought tolerance is further complicated because several types of abiotic stress, such as high temperatures, high irradiance, and nutrient toxicities or deficiencies, can challenge crop plants simultaneously. Although marker-assisted selection is now widely deployed in wheat, it has not contributed significantly to cultivar improvement for adaptation to low-yielding environments, and breeding has relied largely on direct phenotypic selection for improved performance in these difficult environments. Advances in plant breeding to produce improved and higher performing wheat cultivars are key to making dryland food-production systems more efficient and more resistant to pressure from drought, extremes of cold and heat, unpredictable rainfall, and new pests and diseases. For optimal performance, wheat cultivars can be targeted to specific farming systems, depending on local conditions and stresses. Genetic gain in wheat yield potential during the last century has been achieved by plant breeding and is well documented. It has been studied by comparing, in the same field trial, the yield of cultivars characterised by different years of release. Genomic selection (GS) and high-throughput phenotyping (HTP) have attracted the interest of plant breeders, and both approaches promise to revolutionise the prediction of complex traits, including growth, yield and adaptation to stress. This review describes the impact of drought on yield, trends in yield for boosting crop yields to meet the projected demands of rising global population by 2050, and genetic gain achieved by plant breeding in the last decades; and gathers known functional information on the genes, metabolites and traits and their direct involvement in conferring drought tolerance in wheat. In addition, it discusses recently developed techniques (i.e. GS and HTP) integrated with approaches such as breeding, genetics, genomics, and agronomic strategies for improving drought in wheat.

Acid soils (pH <5.0) continue to limit the yields of Australia’s major crops and restrict their cultivation. These soils pose various abiotic stresses that restrict or affect plant growth in different ways. Chief among these stresses is aluminium (Al³ ) toxicity, which inhibits root growth. Soil acidification can occur naturally but certain agricultural practices accelerate the process. The most effective management practice for slowing and reversing acidification is the application of lime (calcium carbonate). Liming has increased over the last 25 years but it can take several years to ameliorate subsoil acidity and the application rates in some areas remain too low to avoid further acidification. If left unmanaged, acidification will degrade agricultural land and cause larger yield losses in the future. Crops that are better adapted to acid soils are important resources because they help to maintain production while amelioration efforts continue. Significant genotypic variation for acid-soil tolerance has been reported in wheat, barley and pulse species and improvements to yield are likely by pyramiding the optimal genetic loci controlling this trait through breeding. Further increases in production might also be possible with wider crosses to related species and through genetic engineering. This review assesses the potential of genetics and biotechnology for increasing the yields of Australia’s major grain crops on acid soils.

Combined high temperature and weak radiation stress negatively influences wheat production. However, related eco-physiological mechanisms across wheat species of different genetic backgrounds are not well documented. A pot-culture experiment was conducted in growth chambers to analyse the prevailing strategies of wheat genotypes with different ploidy levels under combined high temperature and weak radiation (30°C−25°C, 200 µmol m⁻² s⁻¹ photosynthetically active radiation (PAR)) stress compared with normal growth conditions (20°C−15°C; 400 µmol m⁻² s⁻¹ PAR). The diploid and tetraploid wheat genotypes showed better avoidance ability to high temperature and weak radiation stress than the hexaploids. These diploids and tetraploids produced high vegetative biomass under control conditions but this was reduced substantially under the stress. The adaptive response to avoid the stress was a strong reduction in vegetative organs, mainly leaf area. Consequently, these genotypes produced lower yields. By contrast, modern hexaploid wheat varieties displayed a stronger tolerance to the stress and produced higher yields through greater green leaf area, higher relative leaf water content, and higher proline and soluble sugar contents. The relative importance of these tolerance and avoidance strategies was estimated to account for 60% and 22%, respectively, of the variations in grain yield. Our study demonstrated that modern hexaploid wheat has acquired a greater proportion of tolerance rather than avoidance strategy in response to high temperature and weak radiation stress.

Low temperature at the booting stage in rice (Oryza sativa L.) can cause male sterility, resulting in yield losses. A set of chromosome segment substitution lines derived from the varieties Sasanishiki (cold-tolerant, ssp. japonica) and Habataki (cold-susceptible, ssp. indica) was used for analysis across two natural, low-temperature environments to study the genetic basis for cold tolerance at the booting stage. Spikelet fertility was used as the evaluation index for cold tolerance identification. Eight quantitative trait loci (QTLs) for cold tolerance were detected, two of which were located on chromosomes 3 (qCTSF3.1 and qCTSF3.2), and the others on chromosomes 4 (qCTSF4), 5 (qCTSF5), 6 (qCTSF6), 7 (qCTSF7), 8 (qCTSF8) and 9 (qCTSF9). The phenotypic variation explained by each QTL ranged from 5.4% to 25.3%. Of the eight QTLs, six (qCTSF3.2, qCTSF5, qCTSF6, qCTSF7, qCTSF8, qCTSF9) were repeatedly detected in two environments. QTLs qCTSF3.1, qCTSF7 and qCTSF9 overlapped with previously reported QTLs. All tolerant alleles for all QTLs were contributed by Sasanishiki.

Heat stress can frequently limit the yield of Brassica napus L. grown in Canada because of the often unavoidable concurrence of high temperatures and flowering. Ten B. napus inbred genotypes, an open-pollinated B. napus commercial cultivar and a B. juncea genotype were grown in a greenhouse and subjected to two temperature regimes in a growth chamber for 14 days during flowering: control 22°C/10°C and high 31°C/14°C (day/night). Floral buds were sampled at the end of the 14-day treatments, and an untargeted metabolomic assessment was completed using gas chromatography–mass spectrometry. Flower duration, number of flowers, number of pods, biomass, number of seeds and seed weight were recorded. Yield was reduced by 55% in the heat treatment during winter and by 41% during the subsequent autumn experimental run. Of the 12 genotypes, five were classified as heat-tolerant and four as heat-susceptible based on the calculated heat susceptibility index across two experiments. In total, 25 metabolic markers were identified that discriminated between the heat-tolerant and -susceptible genotypes exposed to the heat treatment. The variation identified within this set of germplasm has provided evidence that variation exists within B. napus to enable genetic gain for heat tolerance.

Brassica vegetables are an important source of dietary nutrition. The nutritional quality of mineral elements is becoming one of the most important studied traits because of the year-round supply of vegetables in China. However, there are few reports about breeding and utilisation of mineral elements in non-heading Chinese cabbage (Brassica napus L.). Using two newly reported CMS (cytoplasmic male-sterile) lines of non-heading Chinese cabbage, we conducted incomplete diallel experiments to analyse heterosis, combining ability and cytoplasmic effects for mineral elements such as calcium (Ca), iron (Fe), magnesium (Mg) and zinc (Zn). Heterosis analysis of mineral elements indicated that the crossing combinations A1 (hau CMS) × C03, A2 (eru CMS) × C03 and A2 × C11 exhibited desirable positive effects of mid-parent heterosis and high-parent heterosis in terms of mineral element content that could be exploited for commercial purposes. Analysis of general combining ability (GCA) effects of the parental lines indicated that the tester C11 was superior for the improvement of the four mineral elements; CMS line A1 had greater GCA effects than CMS line A2 for Ca and Fe. The hybrid combinations A2 × C11, B × C05 and B × C12 showed positive specific combining ability (SCA) effects for the four mineral elements on overall performance. The analysis revealed that cytoplasmic effects of hau CMS and eru CMS were both positive for Ca and Fe, and that A1 had more obvious cytoplasmic effects than did A2. These results indicated that the two isonuclear, alloplasmic CMS lines of non-heading Chinese cabbage might be useful for improving the nutritional quality traits of cruciferous vegetables and for heterosis utilisation.

In the high-rainfall zone of south-eastern Australia, deep incorporation of organic matter has previously been reported to increase crop yields by improving access to subsoil water and nutrients, resulting from the amelioration of subsoil constraints. However, previous experiments did not separate the yield response resulting from nutrients contained in the amendment from yield response due to amelioration of subsoil constraints. In order to separate these effects, eight field experiments were conducted on a range of soil types across the medium- and high-rainfall zones of south-eastern Australia between 2014 and 2016. Grain yield and quality responses of a range of annual crops (canola, wheat, barley and lentil) to surface and deep placement of poultry litter and inorganic fertilisers with matched nutrition were assessed. Over 15 site × year combinations, there was no consistent, significant positive interaction between amendment and incorporation treatments necessary to demonstrate that deep placement of amendment (i.e. subsoil manuring) had advantages over surface application of the same amendment. Differences in crop yield in these experiments are attributed to nutrients (particularly nitrogen) supplied by the amendment, and not to the amelioration of subsoil constraints. Future research, including analysis of subsoil physicochemical properties and plant nutrient concentrations after treatment, is necessary to confirm the role of nitrogen and other nutrients in the crop response to subsoil manuring.

Temperature increase assumes a prominent role in the context of expected climate change because of its significant impact on plant metabolism. High temperature can affect the carbon-assimilation pathway at both stomatal and non-stomatal levels, mainly through stomatal closure and photochemical and biochemical limitations. In general, however, plants have some ability to trigger acclimation mechanisms to cope with stressful conditions, especially if the limitations are imposed in a gradual manner during seasonal change. This study aims at evaluating changes at stomatal and photochemical levels in Coffea arabica and C. canephora under exposure to mild temperature (spring) and high temperature (summer). Potted plants were maintained in a greenhouse, watered to field capacity and subject to natural variations of light, temperature and relative humidity. In C. arabica, exposure to summer conditions decreased photosynthetic rates (A), stomatal conductance (g_s) and stomatal density and increased intrinsic water-use efficiency (iWUE) compared with spring values, whereas C. canephora plants maintained similar values in both seasons. However, C. canephora presented lower A and g_s during spring than C. arabica. Because photosynthetic capacity (A_max), photosynthetic performance index and membrane permeability were similar between genotypes and seasons, and maximum quantum yield (F_v/F_m) and photosynthetic pigments were not affected in C. arabica in summer, we conclude that under high temperature conditions, stomatal closure imposes the major limitation on C. arabica photosynthesis in summer. Finally, both coffee genotypes were able to avoid damage to photochemistry pathway under supra-optimal temperatures.

Echium plantagineum is a significant pasture weed in the Mediterranean climatic zone of several countries, including Australia. This invasive weed, introduced as an ornamental into Australia (where it is known as Paterson’s curse), quickly became established and is now a significant weed of agriculture. Although E. plantagineum is a well-established, highly competitive weed that thrives under disturbance and is tolerant of a wide variety of conditions, including varying soil moisture and drought, and some aspects of its ecology remain unknown. This study investigated germination response to temperature and light, pH, soil moisture, salinity, and pre-germination exposure of seed to heat and smoke. Temperature was found to be more influential on germination than light and the species is tolerant to a wide range of pH. However, available moisture may limit germination, as may elevated salinity. Management of this weed requires approaches that minimise soil seedbank input or prevent germination of soil seedbanks.