Search

Climate change may lead to an increase in both day and night time temperatures in rice (Oryza sativa L) growing regions, but the impact of such temperature increases on yields of Australian rice varieties is not known. We evaluated the biomass and grain yield response of eleven Australian rice varieties including long, medium and short grain types, and the Californian cultivar M205, to heat stress during the reproductive phase and grain filling stages. Heat stress (day/night = 35/25°C) was applied at one of three stages: from panicle exertion to anthesis (PE), from anthesis to 10 days after anthesis (EGF) and from 10–20 days after anthesis (LGF) periods after which the effect on biomass and grain yield was compared to control plants. When heat stress was applied at PE and early grain filling stages, mean grain yield losses across rice varieties were 83% and 53%, respectively, though significant genotype × heat stress treatment interactions were observed. Notably, three varieties—YRM 67, Koshihikari and Opus—appeared to possess greater tolerance to heat stress at these growth stages. A significant genotype × heat stress treatment interaction was also observed in the LGF treatment, where significant yield reductions were only observed in Opus (21% loss) and YRM 67 (25% loss). A lack of effect of heat stress on total grain yield in most varieties at late grain filling appeared to be due to late tiller grain yields which were either unaffected by the heat stress or increased significantly compared to control plants. While genetic variation for tolerance to heat stress across the three growth stages was observed, there was no rice genotype that was consistently tolerant (in terms of yield under stress) across all three heat stress treatments. In the absence of a genotype that showed broad heat stress tolerance during reproductive growth, we suggest screening of a wider pool of more diverse rice germplasm is warranted.

Water-soluble carbohydrate accumulation can be selected in wheat breeding programs with consideration of genetic × environmental interactions and relationships with other important characteristics such as relative maturity and nitrogen concentration, although the correlation between WSC traits and grain yield is low and inconsistent. The potential to increase the genetic capacity for water-soluble carbohydrate (WSC) accumulation is an opportunity to improve the drought tolerance capability of rainfed wheat varieties, particularly in environments where terminal drought is a significant constraint to wheat production. A population of elite breeding germplasm was characterized to investigate the potential for selection of improved WSC concentration and total amount in water deficit and well-watered environments. Accumulation of WSC involves complex interactions with other traits and the environment. For both WSC concentration (WSCC) and total WSC per area (WSCA), strong genotype × environment interactions were reflected in the clear grouping of experiments into well-watered and water deficit environment clusters. Genetic correlations between experiments were high within clusters. Heritability for WSCC was larger than for WSCA, and significant associations were observed in both well-watered and water deficit experiment clusters between the WSC traits and nitrogen concentration, tillering, grains per m2, and grain size. However, correlations between grain yield and WSCC or WSCA were weak and variable, suggesting that selection for these traits is not a better strategy for improving yield under drought than direct selection for yield.

Climate change represents a threat to the productivity of staple crops which are sensitive to heat stress. While heat stress during grain filling is known to reduce rice (Oryza sativa) yields, the impact on grain quality traits such as head rice yield (HRY) has not been fully resolved. The impact of a 10 d heat stress event (31/23 °C, 33/24 °C and 35/25 °C: day/night, 12 h/12 h) from 10 days after anthesis (DAA) to 20 DAA on grain yields and HRY was investigated in two medium grain (M205, Baru) and one long grain (Lemont) japonica cultivars and one medium grain indica cultivar (Teqing). Losses during milling were partitioned into husk losses or grain breakage during de-husking, and bran losses or grain breakage during polishing. While the highest heat stress (35/25 °C) reduced grain yields by around 20% compared to control plants across the four cultivars, reductions in HRY were greater than 50%. In the control treatment, husk losses during milling ranged from 21% (Teqing) to 40% (Lemont) while breakage of white rice during milling ranged from less than 5% in M205 and Lemont to 23% in Teqing. High levels of heat stress led to increased grain breakage during dehusking and/or polishing in cultivars M205, Baru and Lemont. However, heat stress reduced cultivar Lemont HRY not by increased grain breakage during polishing but predominantly due to a 59% increase in husk loss. Given husk tissue is not a net carbon source for developing rice grains, this suggests heat stress in Lemont increased carbon partitioning from vegetative tissues to the husk at the expense of the developing caryopsis. Ultimately, our results indicate reduction in HRY due to heat stress during grain filling is complex and cannot be attributed solely to greater grain breakage during de-husking and polishing. While HRY is typically treated as a single trait, our data suggest quantifying the individual process losses that contribute to HRY as separate traits will improve the accuracy of HRY QTL analysis and selection in breeding programs.

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.

To extend the production base of durum wheat in Australia, field trials were conducted on seven registered durum varieties across four seasons and six sites in locations where irrigation was supplied during crop growth. The purpose was to determine if the quality of the grain produced met the requirements for good milling and pasta-making quality and to understand the genotype, environment and their interaction in affecting yield and technological quality of the grain and derived pasta. High grain yields and grain protein were obtained, producing large grain weights, low screenings and low percentage of hard vitreous kernels. Yellow colour of semolina and pasta was reduced marginally but dough and other pasta technological characteristics were similar to typical dryland durum production, with some exceptions. Varieties were identified with potential for production under irrigation.