Average yield of canola in the high-rainfall zone (HRZ) of southern Australia are about half the predicted potential yield based on seasonal water supply. Current cultivars of canola that are available to growers were not bred specifically for the HRZ and tend to be short-season types aimed at escaping water stress during grain filling in the drier regions of the cropping belt. In the HRZ, these cultivars fail to utilise all available growing-season water due to early maturity. Field experimentation and crop simulation studies across the HRZ landscape of south-eastern Australia were used to determine the increased yield potential of longer-season canola cultivars compared with short-season cultivars. In this study the Catchment Analysis Tool spatial modelling framework was used to determine the expected canola yields of three cultivars across the entire HRZ of south-eastern Australia. Hyola50 (‘spring-short’) was used to represent the current recommended spring-type canola cultivar within the HRZ and was evaluated against an unreleased long-season spring-type cultivar CBI8802 (‘spring-long’) and a newly released winter-type cultivar Taurus (‘winter’). Spring-long outperformed spring-short across much of the study area. Yield advantages of winter over spring-short were mainly confined to the coastal fringe of Victoria and Tasmania and small pockets in New South Wales where at one location the average yield over 50 growing seasons exceeded spring-short by up to 60% or 1.4 t/ha. The superior performance of spring-long, (up to 17% or 0.9 t/ha at one location) was over a wider area than winter (26.4 compared with 8.8 million ha for winter) and although the magnitude of the yield increase over spring-short was not as great as winter at some locations, the overall result determined that spring-long had the greater production potential. The superior performance of spring-long beyond the HRZ challenges the trend of selecting earlier maturing cultivars by current breeders following the abnormal sequence of dry years in an attempt to minimise yield loss due to water stress during grain filling. This study has provided breeders, growers and advisors with information on where in the HRZ a longer-season canola cultivar can be grown to improve overall crop productivity. It has also provided evidence that new canola types may be required to maximise grain yields not only for the HRZ but potentially also in lower rainfall regions.

Selection for rapid leaf area growth has the potential to increase wheat biomass, and both water-use efficiency and weed competitiveness early in the season. Several morphological components contribute to increased seedling leaf area, including rapid seedling emergence and production of longer, wider leaves. Early emergence of a large coleoptile tiller has also been demonstrated to increase plant leaf area and biomass in wheat and other grass seedlings. Yet little is known of the extent and nature of genotypic variation for coleoptile tiller growth in wheat. A random set of 35 wheat, barley, and triticale genotypes was evaluated in glasshouse and outdoor studies for seedling characteristics, including coleoptile tiller growth and total plant leaf area. Coleoptile tillers were produced more reliably for seedlings grown outdoors and when supplied with additional soil nitrogen. Genotypic differences in coleoptile tiller frequency and leaf area were large, ranging from 0 to 78% and from 0.0 to 1.4 cm2, respectively at very early growth stages. Australian commercial wheats tended to produce fewer coleoptile tillers of smaller size than overseas germplasm where the coleoptile tiller accounted for up to 12% of total seedling leaf area. This compared favourably with mainstem tiller leaf area, which ranged from 0 to 3.5 cm2 and accounted for up to 16% of plant leaf area. Broad-sense heritabilities were high for coleoptile tiller presence and size in favourable conditions (c. 75%) but low (c. 40%) for seedlings evaluated across nitrogen content-varying soils. Generation means analysis was used to investigate genetic control for coleoptile tiller growth across multiple populations. Significant (P < 0.05) differences were observed among generations for coleoptile tiller frequency and growth (numbers of leaves, leaf area, and biomass). These differences reflected strong additive genetic control with little evidence for any gene action × year interaction. Increases in coleoptile tiller frequency and mass were correlated with larger embryo size and wider seedling leaves to increase seedling leaf area (rg = 0.89). Comparisons between reciprocal F1 and F2 generation means indicated strong maternal effects for coleoptile tiller growth in some but not all crosses. Screening in favourable environments will increase heritability and aid in selection for progenies producing large coleoptile tillers. Evidence for additive genetic control should permit early generation selection but not without some progeny-testing for coleoptile tiller growth together with other early vigour components associated with increased plant leaf area.

Average wheat yields in the high-rainfall zone (HRZ) of southern Australia are predicted to be around 10 t ha–1, yet most regions fall short through a lack of locally adapted cultivars or abiotic stress that constrains yield. Wheat yields in Tasmania can be variable but have exceeded this potential yield in some field trials and have thus approached that of other traditionally high-yielding HRZ environments such as northern Europe. A contributing factor to high wheat yields in Tasmania is the cool-temperate climate, which tends not to have extremes in temperature (cold, heat) as may be experienced in HRZ environments elsewhere. Hence an understanding of crop growth, development and yield of wheat of locally adapted wheat cultivars in Tasmania may improve our understanding of the basis of yield formation in other HRZ in Australia. This was evaluated by conducting an analysis for adaptive response of grain yield in 10 wheat genotypes to a range of 14 environments that were favourable for wheat production or experienced constraints to growth. Crop growth and yield formation was then examined in detail for all or a subset of these genotypes in three field trials with contrasting environments, two of which included a time of sowing (TOS) treatment. Environment accounted for around 90% of the sum of squares (SS) in the multi-site analysis of yield. Six environment groups were identified using cluster analysis, two of which were clearly separated in response to frost at flowering or putative biotic stress, which constrained yield to 1.8 and 6.8 t ha–1, respectively. Waterlogging was also a significant abiotic stress in one of the TOS field trials. The late-flowering cultivar Tennant had the highest yield in the presence of waterlogging and by avoiding frost at flowering, although it suffered a yield penalty of 35 and 66%, respectively, compared with the average across environments. The highest-yielding genotypes averaged 8 t ha–1 across environments and included Alberic, the breeding line K37.18 and the new release Revenue. In the detailed experiments on crop growth and development, high grain yields of 10 t ha–1 in Mackellar appeared to be due to increased grains ear–1, resistance to barley yellow dwarf virus and possibly higher radiation-use efficiency, although the latter needs to be confirmed. There was little genotype × environment interaction for grain yield, hence wheat breeders can have a relatively high level of confidence that genetic material with high yield potential should rank consistently across Tasmanian environments. Results presented in the paper will be useful in developing management and breeding strategies to increase potential yield across the HRZ of southern Australia.