Tina Acuna

Long-season canola ( Brassica napus L.) cultivars offer potential to substantially increase grain yield production in south-eastern Australia compared with current spring cultivars

Abstract. 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.

Use of genotype × environment interactions to understand rooting depth and the ability of wheat to penetrate hard soils

BACKGROUND Root systems are well-recognized as complex and a variety of traits have been identified as contributing to plant adaptation to the environment. A significant proportion of soil in south-western Australia is prone to the formation of hardpans of compacted soil that limit root exploration and thus access to nutrients and water for plant growth. Genotypic variation has been reported for root-penetration ability of wheat in controlled conditions, which has been related to field performance in these environments. However, research on root traits in field soil is recognized as difficult and labour intensive. Pattern analysis of genotype × environment (G × E) interactions is one approach that enables interpretation of these complex relationships, particularly when undertaken with probe genotypes with well-documented traits, in this case, for the ability to penetrate a wax layer. While the analytical approach is well-established in the scientific literature, there are very few examples of pattern analysis for G × E interactions applied to root traits of cereal crops. SCOPE In this viewpoint, we aim to review the approach of pattern analysis for G × E interaction and the importance of environment and genotype characterization, with a focus on root traits. We draw on our research on G × E interaction for root depth and related studies on genotypic evaluation for root-penetration ability. In doing so, we wish to explore how pattern analysis can aid in the interpretation of complex root traits and their interaction with the environment and how this may explain patterns of adaptation and inform future research. CONCLUSIONS With appropriate characterization of environments and genotypes, the G × E approach can be used to aid in the interpretation of the complex interactions of root systems with the environment, inform future research and therefore provide supporting evidence for selecting specific root traits for target environments in a crop breeding programme.

Constraints to achieving high potential yield of wheat in a temperate, high-rainfall environment in south-eastern Australia

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.

Yield and water-use efficiency of wheat in a high-rainfall environment

Abstract. Yield, water use and water-use efficiency (WUE) in the high-rainfall zone of Tasmania are highly variable because of environmental and agronomic constraints to grain production that limit yield potential. The expansion of irrigation infrastructure in Tasmanian production systems with access to low-cost, plentiful irrigation sources will also influence these components in some areas. This paper reports on desktop modelling studies that aimed to benchmark wheat WUE and to explore the sensitivity of yield, water use and WUE to changes in management practice in a high-rainfall environment. Here, WUE was defined as: grain yield/(evapotranspiration + drainage + runoff). The crop simulation model APSIM-Wheat was used to quantify key water balance elements and estimate ‘attainable’ and ‘potential’ WUE and grain yield for 27 wheat trials. The upper limit for WUE was ∼30 kg/ha.mm in excess of 180 mm evaporation, which is 16% higher than previous estimates at this southerly latitude for wheat. Attainable WUE ranged from 58% to 100% of potential WUE and was limited by nitrogen supply and water loss through evaporation, drainage and runoff. Model scenarios showed that co-limitation of inputs of nitrogen and irrigation was an important driver of grain yield and WUE. The implications of this research on crop management and production in temperate, high-rainfall environments are discussed.

Can soil crusting be reduced through application of gypsum, organic waste, and phosphoric acid?

Soil crusting is a form of land degradation in which the breakdown of aggregates results in the formation of a thin impermeable layer on the soil surface. An earlier pilot trial indicated that application of paper waste, gypsum, phosphoric acid, and covering the soil surface with wire mesh showed potential for reducing soil crusting. This study was established to evaluate the use of products for reducing the severity of soil crusting, while also testing different approaches for measuring the severity and likelihood of soil crust formation. Gypsum was applied at 0.25 and 0.50 kg m−2 (low rate [LG] and high rate [HG], respectively), paper waste was applied at 1, 2.5, and 7.5 kg m−2 (low [LPW], moderate [MPW], and high [HPW] rates, respectively), and phosphoric acid was applied at 80 and 160 mL m−2 (low rate [LP] and high rate [HP], respectively). Combinations of these products were made including (1) wire mesh (WM) and 0.50 kg m−2 gypsum (WM + HG); (2) 0.50 kg m−2 gypsum and 80 mL m−2 phosphoric acid (HG + LP); (3) 2.5 kg m−2 paper waste, 0.50 kg m−2 gypsum, and 80 mL m−2 phosphoric acid (MPW + HG + LP); and (4) 7.5 kg m−2 paper waste and 160 mL m−2 phosphoric acid (HPW + HP). The likelihood of crust formation was inferred from aggregate stability determined by rainfall simulation and wet sieving, while the severity of soil crusting was inferred from crust density, hydraulic conductivity, and penetration resistance. The four measures of crust severity/likelihood were highly correlated with each other (R2 = 0.57 to 0.80). The HPW + HP, MPW + HG + LP, and MPW treatments increased hydraulic conductivity by 72%, 66%, and 45%, respectively; increased aggregate stability determined by rainfall simulation by 28%, 37%, and 39%, respectively; reduced surface density by 10%, 7%, and 6%, respectively; and reduced penetration resistance by 33%, 37%, and 34% as average at all five sampling dates (days 8, 14, 28, 71, and 197). Moreover, the high rate of gypsum significantly reduced bulk density by 7% and penetration resistance by 26%, yet had no effect on any other measure of crusting. Phosphoric acid (HP) significantly increased aggregate stability determined by rainfall simulation by 29% (days 8, 14, 28, and 71), reduced bulk density by 6% (days 8 and 14), and increased hydraulic conductivity at day 8 by 110%. Reduced severity and or likelihood of crust formation following application of gypsum and paper waste were attributed to the increase in calcium cations (Ca+2) and soil organic carbon (C). The paper waste and gypsum were the most effective amendments over the duration of the trial, while phosphoric acid reduced the severity of crust formation in the 14 days after application. Recommendations are provided on the efficiency of different approaches for measuring soil crusting, in which penetration resistance is preferable because of its high correlation with other measurements and being the least time consuming.

Effect of endophyte association with Brachiaria species on shoot and root morpho-physiological responses under drought stress

A greenhouse experiment was conducted at the International Centre for Tropical Agriculture in Colombia to evaluate effects of the fungal endophyte, Acremonium implicatum, on growth and physiological responses of five Brachiaria cultivars. Plants were grown under well-watered (WW) and drought-stressed (DS) conditions, with (E+) and without (E-) endophyte; and their morpho-physiological responses were determined. Significant two-way and three-way interactions produced variable effects on leaf area, number of tillers, shoot elongation, shoot biomass, total root diameter, diameter of cortex, area of stele and diameter of xylem vessel. Main effect of endophyte significantly increased leaf stomatal conductance and reduced diameter of xylem. Smaller leaf area was found in endophyte-infected than control plants of three cultivars, both under WW and DS conditions, which indicates a cost of endophyte infection to the host cultivars. Large root diameter and area of stele under WW conditions, as well as small diameter of xylem vessels in some cultivars suggests that endophyte may improve efficiency for water uptake and use under different water regimes. Less Root Cortical Aerenchyma (RCA) was observed in endophyte-infected plants of Tully and Cayman than the control, which may influence plant capacity for resource acquisition in Brachiaria. Genotype-specific variation among hosts generally segregated the cultivars in terms of their shoot and root responses, based on presence (E+) or absence (E-) of endophyte. However, future studies should examine how association of A. implicatum with Brachiaria grass affects capacity for water uptake and carbon accumulation, and the role of RCA in these processes.

Implementing the Threshold Learning Outcomes for Agriculture at university

The national Learning and Teaching Academics Standards statement for agriculture (AgLTAS) describes the nature and extent of the discipline and threshold learning outcomes (TLOs) that define what a graduate should know and understand and what core skills they should have at graduation. The AgLTAS statement has been endorsed by the Australian Council of Deans of Agriculture and can be used to communicate to current and future students the minimum standards of their degree, as well as be used to inform curriculum design. While the AgLTAS document provides explanatory notes to assist educators to further understand the intent of the TLOs there are no exemplars on how the AgLTAS standards can be implemented. We will present two case studies of how academics at the University of Tasmania and the University of Adelaide used the AgLTAS to map their respective agriculture curricula. An online Curriculum Mapping Tool (CMT) was used to evaluate the alignment between the curriculum and the TLOs and to identify gaps in the curriculum where improvement may be required. Workshop participants completed pre- and post-workshop questionnaires to evaluate the benefits of mapping the curriculum for the respective degrees against the AgLTAS TLOs. The pre-workshop questionnaire collected demographic data about the participants and their knowledge about the agriculture TLOs, degree and the Australian Qualifications Framework. The post-workshop questionnaire established perceived changes in each participant’s awareness, knowledge, connection with the teaching team and curriculum. It was also used to inform the development of the explanatory notes section in the AgLTAS statement. In addition, four units from each University were chosen randomly for external benchmarking. The output from the CMT demonstrated that the degrees met or in some instances exceeded the graduate level TLOs for agriculture. Determining the proficiency level for a TLO can be an issue, as to the difference between explicit learning outcomes that might be expected at introductory level, but which at advanced levels are regarded as implicit. External reviewers examined the curricula of courses at the two Universities for alignment to the TLOs to identify and enable correction for academic bias in internally mapping units. The external evaluation aligned well with the results from the CMT. A combination of external review and curriculum mapping workshops involving the entire teaching team is however still recommended when mapping degrees to TLOs. The process of curriculum mapping was shown to provide most academics with a more holistic view of how the degree meets the AgLTAS and has the potential to drive innovation in assessment design. Curriculum mapping also assisted academics by reinforcing their understanding of constructive alignment between assessment and learning outcomes at the unit, course and the discipline threshold standards. We will also provide commentary on what we believe is the next steps and implications of the AgLTAS for curriculum development, industry engagement and graduate employability in the agriculture discipline.