Moisture stress limits the yield and productivity of wheat, a staple food for 35% of the world’s population. The reproductive stage is the most vulnerable to moisture deficit, and genetic variation for tolerance to stress has been identified in the wheat gene pool. Introducing this complex variation into new, pure-line cultivars is difficult and time consuming. However, varietal mixtures can be an effective alternative to traditional gene pyramiding. Varietal mixtures lessen the impacts of abiotic and biotic stresses in two ways. First, they buffer yield through more efficient resource use, including soil moisture, particularly evident when mixtures comprise complementary physiological traits that influence water-use efficiency. Second, they improve resistance to root diseases and pests that limit root growth and subsequent access to, and absorption of, water from deeper in the soil profile. This review evaluates the concept of varietal mixtures and assesses their impact on crop productivity and environmental buffering. The potential of physiological and root disease resistance trait mixtures to stabilise yield is also explored. Avenues for developing compatible mixtures based on physiological traits that increase yield in water-limited environments are evaluated.

Salinity is one of the most serious problems of crop production worldwide. In this research, a set of different wheat landraces with high diversity collected throughout Iran, advanced lines in breeding programs, and some well-known tolerant and sensitive cultivars were used to estimate genetic parameters of agronomic traits by using the restricted maximum likelihood (REML) approach. The results showed that several genotypes such as BUMI8, Salt18, BUMI1, Check cultivar and Salt25 had no reduction in grain yield under saline conditions compared with normal conditions. Minimum reductions in grain yield were related to BUMI6, Roshan and Shahpasand genotypes. High broad-sense heritability for most traits showed that they could be used to select and improve the salt tolerance of wheat germplasm in breeding programs. Grain yield had high broad-sense heritability under normal (H²_b = 0.61) and saline (H²_b = 0.55) conditions. Traits related to height and number of spikes per plant showed a positive correlation with grain yield. Time to heading and to maturity showed negative correlation with grain yield. Number of kernels per spike, kernel weight per spike, number of spikes per plant and spike weight showed positive correlations with grain yield under saline conditions. A significantly negative correlation was also seen between grain yield and days to heading or days to maturity under saline conditions. High variation and moderate to high heritabilities of yield and yield components in normal and salt-stressed field conditions for Iranian bread wheat germplasm are promising to enhance the narrow genetic pool of salinity tolerance.

Research into winter cereal breeding in Australia has focused primarily on studying the effects of rainfed environments. These studies typically show large genotype × environment (GE) interactions, and the complexity of these interactions acts as an impediment to the efficient selection of improved varieties. Wheat has been studied extensively; however, there are no published studies on the GE interactions of triticale in Australia under irrigated production systems. We conducted trials on 101 triticale genotypes at two locations over 4 years under intensive irrigated management practices and measured the yield potential, GE interactions, heritability and estimated genetic gain of yield, lodging resistance and several other traits important for breeding triticale. We found that high yield potential exceeding 10 t ha^–1 exists in the Australian germplasm tested and that, in these irrigated trials, genotype accounted for a high proportion of the variability in all measured traits. All genetic parameters such as heritability and estimated genetic gain were high compared with rainfed studies. Breeding of triticale with improved yield and lodging resistance for irrigated environments is achievable and can be pursued with confidence in breeding programs.

In order to increase yield and water productivity, arrest the mining of groundwater, and achieve quality production in Northwest India, there is a need to optimise the transplanting time for newly evolved, high-yielding basmati cultivars. This study in the Indian Punjab was aimed at investigating the effect of date of transplanting (5, 15, and 25 July) on yield, quality traits, and water productivity of four basmati rice cultivars (Pusa Basmati 1121, Pusa Basmati1509, Punjab Basmati 3, and Basmati 386) varying in photoperiod sensitivity. Water productivity of Pusa Basmati1509 was higher than of photoperiod-sensitive cultivars (Punjab Basmati 386 and Punjab Basmati 3) for each transplanting date. Water productivity [irrigation, WP_I; total (irrigation   rainfall), WP_{I R}; and real crop, WP_ET] of Punjab Basmati 3 for the 25 July transplanting was similar to Pusa Basmati 1509 for the 5 July transplanting. For the 25 July transplanting, WP_I, WP_{I R}, and WP_ET of Pusa Basmati 1509 increased by 48.9%, 35.2%, and 22.5%, respectively, relative to Pusa Basmati 1121; by 34%, 31.4%, and 27.5% relative to Punjab Basmati 3; and by 81.1%, 70.4%, and 56% relative to Basmati 386. The study showed that delaying transplanting of photoperiod-sensitive and short-duration, photoperiod-insensitive basmati cultivars helped to improve water productivity and quality traits, particularly the head rice recovery (%), kernel length after cooking, and amylose content.

Physiological drought stress responses were assessed in recombinant inbred lines (RILs) from three soybean (Glycine max (L.) Merr.) crosses, in preparation for quantitative trait locus (QTL) analyses using Diversity Arrays Technology (DArT) markers. The three RIL populations were derived from pairwise crosses between three genotypes, cv. Valder, CPI 26671 and G2120, which in previous studies had differed in drought-stress response. Of particular interest was the landrace variety G2120, which in the previous reports had recovered better after severe drought. To assess drought-stress response, the plants were grown in deep cylindrical pots in the glasshouse and exposed to severe water deficit followed by re-watering. Two plants to be genotyped were grown in each pot, together with one plant of G2120, which served as a reference plant against which the responses of the two other plants were assessed. Traits recorded included measures of relative water content (RWC), epidermal conductance (g_e) and recovery in growth following re-watering. The responses in the reference and parental plants and the RIL populations were broadly consistent with previous studies. As plant-available water in the soil declined, both RWC and g_e declined, although the relation between RWC and g_e was exponential, rather than linear as in previous studies. Analysis of variance revealed large environmental effects on most of the traits, which resulted in high coefficients of variation and low estimates of broad-sense heritability. However, there were significant differences at both the population and genotype levels for all key traits, confirming the presence of genetic variation for drought-stress response. Some opportunities for enhancing the observed genetic differences and reducing the environmental noise in future studies are canvassed. Application of the observed phenotypic data reported in this paper in subsequent QTL analyses based on DArT markers is reported in the companion paper.

This study applied newly developed Diversity Arrays Technology (DArT) and soybean and mungbean DArT libraries for quantitative trait locus (QTL) linkage analysis in recombinant inbred lines (RILs) from three soybean crosses that had previously been assessed for physiological response to severe drought stress. The phenotypic assessments had identified statistically significant genetic variation among and within the RIL populations and their parents for three drought-related responses: epidermal conductance (g_e) and relative water content (RWC) during stress, and plant recovery after stress. The new linkage maps containing only DArT markers for the three populations individually contained 196–409 markers and 15–22 linkage groups (LGs), with an aggregate length ranging from 409.4 to 516.7 cM. An integrated map constructed by using the marker data from all three RIL populations comprised 759 DArT markers, 27 LGs and an expanded length of 762.2 cM. Two populations with the landrace accession G2120 as a parent, CPI 26671 × G2120 (CG) and Valder × G2120 (VG), respectively contained 106 and 34 QTLs. In each of these populations, 10 LGs harboured QTLs associated with RWC, g_e and recovery ability, of which six similar LGs were associated with drought tolerance. A BLAST (Basic Local Alignment Search Tool) search for sequences of 19 selected DArT markers linked to QTLs conditioning the drought-response traits indicated that 18 DArT markers were unique and aligned to 12 soybean chromosomes. Comparison of these sequenced DArT markers with other markers associated with drought-related QTLs in previously reported studies using other marker types confirmed that five of them overlapped, whereas the remaining 13 were new. Except for chromosome 15, the chromosomes with which the DArT QTLs in the CG and VG populations were associated were those that had been shown to harbour drought-related QTLs in previous studies. A BLASTx protein database search identified soPt-856602 as being associated with the gene for a probable glycosyltransferase At5g03795-like isoform X1 on chromosome 6. Although the several QTLs identified in the study were all of relatively minor effect, it was concluded that, because the DArT technology involves large numbers of markers and enables many lines to be genotyped simultaneously, it should help the process of manipulating multiple QTLs and so enhance their likely cumulative effect.

Pearl millet (Pennisetum glaucum L.) is an important fodder and is a potential feedstock for fuel ethanol production in dry areas. Our objectives were to assess the effect of elevated CO₂ and/or reduced irrigation on biomass production and levels of sugars and proteins in leaves of pearl millet and to test whether mycorrhizal inoculation could modulate the effects of these abiotic factors on growth and metabolism. Results showed that mycorrhizal inoculation and water regime most influenced biomass of shoots and roots; however, their individual effects were dependent on the atmospheric CO₂ concentration. At ambient CO₂, mycorrhizal inoculation helped to alleviate effects of water deficit on pearl millet without significant decreases in biomass production, which contrasted with the low biomass of mycorrhizal plants under restricted irrigation and elevated CO₂. Mycorrhizal inoculation enhanced water content in shoots, whereas reduced irrigation decreased water content in roots. The triple interaction between CO₂, arbuscular mycorrhizal fungi (AMF) and water regime significantly affected the total amount of soluble sugars and determined the predominant soluble sugars in leaves. Under optimal irrigation, elevated CO₂ increased the proportion of hexoses in pearl millet that was not inoculated with AMF, thus improving the quality of this plant material for bioethanol production. By contrast, elevated CO₂ decreased the levels of proteins in leaves, thus limiting the quality of pearl millet as fodder and primary source for cattle feed.

Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum, is an important disease of oilseed brassicas, yet the susceptibility of Australian varieties is unknown. Fifty-five historic, current and potential new Australian canola and mustard varieties were field-screened to determine their relative levels of resistance to SSR. Mean lesion length following stem inoculation with a highly virulent isolate (MBRS1) of the prevailing S. sclerotiorum pathotype (76) ranged from 3.0 mm in the B. napus cultivar Mystic to 202.6 mm (P < 0.001). Three recently developed B. juncea varieties or breeding lines, Sahara, JB0T-908982 and Xceed X121 CL, were extremely susceptible to S. sclerotiorum (mean lesion lengths 90.6, 132.3 and 202.6 mm, respectively). Histological study showed that the high level of resistance in Mystic was associated with strong deposition of lignin in stem cortical cell walls to form a barrier between the invading pathogen and the vascular tissues. Lack of association between mean lesion length and the year of varietal release (R² = 0.005) shows that there has been no improvement in level of resistance to SSR in Australian canola and mustard varieties over the last two decades. Although the very high susceptibility of a few B. juncea varieties demonstrated the value of SSR resistance present in B. napus varieties, this level of resistance is inadequate to prevent ongoing, severe yield losses from SSR under conditions conducive for disease development. Breeding programs can immediately utilise the SSR resistance in Mystic, and other recently identified resistances. This will enable a shift from the current dependence on fungicidal control to reliance on cost-effective, sustainable host resistance as the basis for better management of SSR.

A single functional leaf is usually sampled to evaluate the growth and photosynthetic assimilation of crops. However, there is large variation between leaves in winter oilseed rape (Brassica napus L.) at seedling stage. In this study, the morphological and physiological characteristics of various functional leaves were compared with characteristics of the whole plant at seedling stage for 2 years by using the oilseed rape cultivars Huaza 9 and Huaza 62 as plant material. The aim of this study was to identify a leaf that can represent the whole plant for assimilate accumulation characteristics at the seedling stage of the crop. The results showed that the photosynthetic rate and the contents of non-structural carbohydrates, nutrients and soluble proteins in fourth and fifth leaf of a plant were most closely related to those of the whole plant. The area and dry matter (DM) of all functional leaves were well correlated with those of whole plant, with the fifth leaf having the highest correlations. It is therefore recommended that the fifth leaf is most suitable to represent the whole plant for evaluation of growth and assimilate accumulation for winter oilseed rape at the seedling stage. The following regression equations for whole plant (y) and fifth leaf (x, dry matter or length × width) can be used to predict (1) DM accumulation (g) and (2) total leaf area (cm²) of the whole plant: (1) y = 3.32x   1.51 (R² = 0.88, P < 0.001); (2) y = 1.24x   222.69 (R² = 0.67, P < 0.001).

Introgression of genes from Trifolium uniflorum L. into T. repens L. (white clover) is being investigated as a method to improve phosphorus (P) use efficiency in white clover; however, little is known about the edaphic adaptations or P physiology of T. uniflorum. Growth responses to added P of T. uniflorum, T. repens and some T. repens × T. uniflorum hybrids were determined in a glasshouse experiment in pots of soil. Trifolium uniflorum showed traits consistent with adaptation to low-P soils: slow growth rate, small leaves, relatively high leaf-tissue P concentrations, and sequestration of P in its roots when soil P levels were increased. The response of Kopu II, one of the hybrid backcross parents, was quite different; it showed high growth rate, large leaves, much lower leaf P concentrations, and a large decrease in root : shoot P allocation as soil P increased. Tahora, the other backcross parent, exhibited several characteristics that were intermediate between Kopu II and T. uniflorum, probably reflecting its breeding origins from New Zealand hill-country ecotypes. This study confirms the potential for interspecific hybridisation with T. uniflorum to increase the tolerance of white clover to low soil P levels, through incorporation of traits related to edaphic adaptations. Variation among the hybrid families in their response to changing soil P confirmed previously published conclusions about the need to screen widely in hybrid material.

Plantation-grown Melaleuca alternifolia (tea tree) is the principal source of tea tree oil in Australia. Upland and coastal ecotypes of tea tree were grown in a common environment to test responses in root, shoot and developmental attributes to four hydrological conditions. Consistent with its wetland origins, tea tree exhibited morphological adaptations for flood tolerance, with both ecotypes possessing a similar maximal capacity for adventitious roots and aerenchyma. Despite adaptation to flood, growth was reduced under prolonged flood relative to a well-watered control, and to a similar degree in both ecotypes. Coastal plants responded more rapidly to flood, suggesting that upland plants may delay costly morphological modifications until flooding is more protracted. Mild water deficit (drought) had a greater impact on growth and development than flooding, and upon coastal than upland plants. Relatively lower impact of drought on biomass and branch whorl number in upland plants was probably due to a constitutively higher root : shoot biomass ratio buffering against retarded development and growth. This study was the first step in identifying genetically controlled abiotic stress tolerances that may be useful for further domestication of tea tree. The potential to improve drought tolerance appeared most promising; however, further work will require consideration of appropriate breeding strategies given the low-resource-adapted population origins of tolerance alleles, and it should be prefaced by a clear definition of the target deployment environment and include testing of yield variables of economic value in target environments.