Weed control in broadacre cropping systems is becoming increasingly difficult owing to widespread evolution of herbicide resistance in major weed species. The importance of crop competition in weed management is often overlooked but it can play an important role in cropping systems. Competitive ability of 86 wheat (Triticum aestivum L.) genotypes varying for early vigour was investigated at two sites over two growing seasons against cultivated oats (Avena sativa L.) as a weed mimic. There were significant (P < 0.001) treatment effects of weed, wheat genotype and weed × genotype interaction at the different sites. Mature crop height and early crop vigour were strongly correlated with improved weed suppression and tolerance. Negative correlation between early vigour (normalised difference vegetation index and visual score) and weed-free yield indicates the presence of some yield penalty in high-vigour (HV) lines. Wheat genotypes with high grain yield under weed-free conditions tended to suffer high yield loss from weeds (low tolerance) and allowed greater production of weed seed (low weed suppression). However, many of the HV lines produced significantly higher grain yield than the tested commercial cultivars under weedy conditions. The use of the Finlay–Wilkinson regression approach for assessing cultivar stability revealed a strong association between genotype mean weed suppression and stability across the four environments. Several HV lines showed consistently greater weed suppression than the wheat cultivars investigated. Genotypic variation was much greater for weed suppression than weed tolerance, suggesting greater opportunity for the selection of improved weed suppression in wheat. However, strong positive correlation between weed suppression and tolerance (r = 0.79, P < 0.001) suggests that wheat lines selected on the basis of high weed suppression may also exhibit improved weed tolerance.

Waterlogging stress is one of the limiting factors influencing wheat (Triticum aestivum L.) production. Wheat tolerance to waterlogging is related to the duration of the waterlogging event, the crop development stage in which waterlogging occurs, and the sensitivity of genotype. In this paper we investigated the impact of eight waterlogging durations (from 0 to 60 days) imposed at 3-leaf and 4-leaf growth stages (∼30 and 40 days after sowing) on grain yield, grain yield components, straw and root dry weight and nitrogen concentration of grain, straw, and roots of two cultivars of wheat. The results showed that of the two cultivars, one (cv. Blasco) was tolerant to waterlogging and the other (cv. Aquilante) was sensitive, thus confirming that there are high genotypic differences in terms of tolerance to waterlogging in wheat. The sensitive cultivar showed a significant reduction in grain yield and straw and root dry weight only when waterlogging was prolonged for more than 20 days. Waterlogging depressed the grain yield of the sensitive cultivar, slowing tiller formation and consequently preventing many culms from producing spikes. It slowed down spikelet formation, consequently reducing the number of spikelets per spike, and reduced floret formation per spikelet, thus reducing the number of kernels per spike.

Heat and drought are among the major obstacles confronting crop production under climate change. The present study was conducted to evaluate 50 diverse wheat genotypes for cell membrane stability (CMS) and chlorophyll content at seedling and anthesis stages under heat and drought stress conditions, to understand the effect of the two abiotic factors and to find promising genotypes for future breeding. Experiments were conducted in the glasshouse (seedling stage) and the field (anthesis stage). Analysis of variance showed significant variation (P ≤ 0.05) for all of the traits at seedling and anthesis stages. High levels of broad-sense heritability and genetic advance at 5% selection intensity indicated the presence of a high genetic component of variation and potential for genetic improvement through selection among the existing genetic variation. CMS showed a significant positive correlation with 1000-grain weight (TGW) under heat and drought conditions at both seedling and anthesis stages. Chlorophyll a/b ratio at seedling stage exhibited a significant negative correlation (r = –0.39, P < 0.05) with TGW under heat stress. Total chlorophyll content was significantly (r = 0.42, P < 0.05) correlated with TGW under heat stress at anthesis. Genotypes ETAD248 and ETAD7 showed the highest CMS and TGW values, whereas their chlorophyll a/b values were lowest, at both seedling and anthesis stages under heat and drought stress conditions. Higher CMS and total chlorophyll content, and lower chlorophyll a/b, were found to be useful indicators to identify genotypes with high TGW under heat and drought stress conditions. This study indicated the possibility of using seedling resistance as an indicator for later stage response in breeding for heat and drought resistance. The resistant genotypes identified can be used as potential germplasm in breeding programs.

Yellow spot (caused by Pyrenophora tritici-repentis) is a major foliar disease in wheat (Triticum aestivum) that has become more serious in recent years, possibly because of climate change. A major quantitative trait locus (QTL) located on the short arm of wheat chromosome 2B explaining 30–40% of the phenotypic variance has been identified as responsible for resistance to Australian yellow spot isolates, which reportedly produce mostly the ToxA effector. The closest marker linked to this QTL was a DArT marker not easy to use in large-scale selections, whereas the closest PCR-based marker available (2.7 cM) was too far away for reliably tagging the locus in wheat breeding. We therefore undertook studies to develop more closely linked and user-friendly markers for this major QTL. Forty-one new markers either synthesised from DArT markers or identified from the GrainGene database were assessed. From these, we developed a new PCR-based marker (Rfsts1), located 0.3 cM away from the major QTL. This is the first suitable marker for marker-assisted selection for yellow spot resistance in Australian wheat-breeding programs.

Our understanding of the contribution of crop root residues to phosphorus (P) cycling is mainly derived from studies using excavated roots re-introduced to soil. This study aims to quantify total below-ground P (BGP) of mature canola in situ and to estimate directly the proportion accessed by subsequent wheat. ³³P-Labelled phosphoric acid was fed by stem wick to canola (Brassica napus) grown in sand or loam in pots. Shoots were removed from all plants at maturity. Half of the pots were destructively sampled. After a 3-week fallow, wheat was grown for 5 weeks in the remaining undisturbed pots. At canola maturity, 23–36% of the ³³P was partitioned in recovered roots and 34–40% in the soil. More ³³P was recovered in the loam than the sand. Within the soil, 6–10% of the fed ³³P was present in resin P and 3–5% was in hexanol-released P pools. Ratios of shoot P : BGP (8 : 1 in sand and 15 : 1 in loam) were much narrower than those of shoot P : recovered root P (17 : 1 in sand and 39 : 1 in loam). A greater proportion and amount of the mature canola BG³³P was recovered by wheat grown in the loam (26%, 2.6 mg/plant) than in the sand (21%, 1.5 mg/plant). The majority of canola BG³³P remained in the bulk soil. Input of P below-ground by mature canola and subsequent P benefit to wheat was greater in loam than sand. The P from canola below-ground residues contributed up to 20% of P uptake in wheat during the first 5 weeks of growth. Longer term benefits of P from below-ground residues require investigation.

As well as being part of the wider gene pool of cultivated species such as mungbean and cowpea, Vigna lanceolata Benth. is of agronomic interest as a potentially useful species in its own right. It is widely adapted across northern Australia from the coast to inland desert regions, and possesses attributes that make it potentially suited as a ley, cover crop or pasture legume in seasonally arid tropical environments. The species comprises several morphotypes that variously differ in their broad geographic distribution, life cycle, habit, edaphic adaptation and/or amphicarpy. In order to assess the potential for breeding improved cultivars, eight representative accessions were hybridised in a complete diallel cross and the viability and fertility of the resultant hybrid progeny evaluated. Of the 56 parental combinations in the diallel, 33 resulted in healthy F₁ hybrid plants, and of these, nine were at least partly self-fertile. Six of these combinations were the reciprocal crosses between three of the perennial, tuberous-rooted, amphicarpic morphotypes. Another two were the reciprocal crosses between the two annual morphotypes. The patterns of relatedness among accessions indicated by the cross-pollination studies were broadly supported by DArT molecular marker analyses, and suggested that there has been some genetic differentiation within the V. lanceolata complex. Although the process of speciation remains far from complete, the levels of genetic compatibility between some morphotypes would be inadequate to enable a breeding program to draw easily on the full range of genetic diversity within V. lanceolata. Two plausible breeding options are suggested. The first is the development of perennial, tuberous-rooted, amphicarpic ideotypes suited perhaps as pasture or understorey legumes, drawing on selected accessions from the three perennial morphotypes, where there was sufficient genetic compatibility and which collectively have wide geographical spread. The second is an annual, freely seeding, fibrous-rooted, amphicarpic ideotype suited perhaps for use as a self-regenerating ley legume, drawing on selected accessions from the two annual morphotypes.

Oilseed rape (Brassica napus L.) yield is strongly decreased by water deficit, and crop-management solutions are urgently required considering the emerging difficulties in breeding for drought-tolerant varieties. Film-forming antitranspirants (polymers) are agrochemicals that, applied to the crop canopy, mechanically block the stomata and decrease canopy transpiration. In this study, the drought-protection efficacy of an adaxial-surface application at the flowering stage of two film-forming treatments (poly-1-p-menthene and di-1-p-menthene) was investigated in pot-grown, droughted oilseed rape over two glasshouse experiments. Over the drought period, the two compounds reduced leaf stomatal conductance (P < 0.001), and as the soil moisture deficit increased, they sustained carbon assimilation and improved water-use efficiency with differing efficacy. Following the antitranspirant treatments, ABA concentration in leaves and reproductive organs was severely reduced and this was accompanied by significant improvements in leaf and flower–pod water potential. Drought significantly decreased the seed dry matter production of oilseed rape plants, by 39% on average. The treatments significantly increased seed dry matter by 13% (poly-1-p-menthene) and 17% (di-1-p-menthene), on average, compared with the unsprayed droughted plants, as a result of a significant increase in number of pods per plant, by 11% and 13%, respectively. The results suggest that film-forming compounds may be a useful crop-management tool to avoid severe drought-induced yield losses in oilseed rape by improving water-use efficiency and plant water status, thus alleviating ABA signalling under water deficit.

In tropical dairy production systems, where high rates of urea fertiliser are applied, little is known about nitrogen (N) fertiliser response, fertiliser-use efficiency and losses to the environment. This study aimed to determine the effects of N fertiliser (urea) application rate and a nitrification inhibitor (3, 4-dimethylpyrazole phosphate, DMPP) on pasture yield and N losses in a dairy production system in North Queensland, Australia. The experiment was a factorial design with two fertiliser rates (industry standard per application 57 kg N ha^–1 or half that, applied ~3-weekly), two DMPP rates (0 or 4.86 g kg^–1 urea) and four replicates, completed over 1 year. Urea applied at half the industry standard rate, together with DMPP, provided annual dry matter pasture yields (11 462 kg ha^–1) not significantly different from those when urea was applied at the higher rate, with or without DMPP (10 691 and 11 156 kg ha^–1, respectively). The low rate of urea without DMPP had the lowest annual dry matter yield (8386 kg ha^–1). Most of the fertiliser N lost from the system appeared to be via leaching, with loss in surface runoff minimal. During the ryegrass phase, an experiment with ¹⁵N labelling showed that, 3 months after application, 27–39% of the applied N had been taken up by the pasture, 23–45% was recovered in the soil, and 18–40% had been lost. Emission of N₂O peaked within a day of fertiliser application, and DMPP did not reduce emissions during that period. The findings indicate good potential for farmers to use DMPP-treated urea as a means of reducing N fertiliser rates without loss of productivity and with less loss of N to the environment.

Accurate assessment of standing pasture biomass in livestock production systems is a major factor for improving feed planning. Several tools are available to achieve this, including the GrassMaster II capacitance meter. This tool relies on an electrical signal, which is modified by the surrounding pasture. There is limited knowledge on how this capacitance meter performs in Mediterranean pastures. Therefore, we evaluated the GrassMaster II under Mediterranean conditions to determine (i) the effect of pasture moisture content (PMC) on the meter’s ability to estimate pasture green matter (GM) and dry matter (DM) yields, and (ii) the spatial variability and temporal stability of corrected meter readings (CMR) and DM in a bio-diverse pasture. Field tests were carried out with typical pastures of the southern region of Portugal (grasses, legumes, mixture and volunteer annual species) and at different phenological stages (and different PMC). There were significant positive linear relations between CMR and GM (r² = 0.60, P < 0.01) and CMR and DM (r² = 0.35, P < 0.05) for all locations (n = 347). Weak relationships were found for PMC (%) v. slope and coefficient of determination for both GM and DM. A significant linear relation existed for CMR v. GM and DM for PMC >80% (r² = 0.57, P < 0.01, RMSE = 2856.7 kg ha^–1, CV_RMSE = 17.1% to GM; and r² = 0.51, P < 0.01, RMSE = 353.7 kg ha^–1, CV_RMSE = 14.3% to DM). Therefore, under the conditions of this current study there exists an optimum PMC (%) for estimating both GM and DM with the GrassMaster II. Repeated-measurements taken at the same location on different dates and conditions in a bio-diverse pasture showed similar and stable patterns between CMR and DM (r² = 0.67, P < 0.01, RMSE = 136.1 kg ha^–1, CV_RMSE = 6.5%). The results indicate that the GrassMaster II in-situ technique could play a crucial role in assessing pasture mass to improve feed planning under Mediterranean conditions.

Development of forage grass genotypes which maintain a high level of performance over a wide range of environments is a goal of most breeding programs. In this study the additive main effects and multiplicative interactions (AMMI) model analysis was used to understand the complexity of genotype by environment interaction and to evaluate the adaptability and yield stability of some tall fescue genotypes and their selected polycross progenies. Replicated forage yield data of 72 genotypes (24 parental, 24 early flowering and 24 late flowering progenies) from six main cropping seasons (2008–14) at two locations and under two levels of irrigation were used for this purpose. The AMMI-1 analysis results accounted for 47.6% of the genotype by environment interaction. Interaction patterns revealed by AMMI-1 biplots indicated that most of the tall fescue genotypes were narrowly adapted and among all evaluated genotypes, only four genotypes (G22, G50, G62 and G65) with yield performance above the average were considered broadly adapted. The AMMI-1 mega-environment analysis indicated that all the environments in Lavark were grouped in one mega-environment, except for E1 and E2. For this mega-environment the winning genotypes were the genotypes G9, G48 and G72. The environments in Isfahan location, except for E13, were grouped in another mega-environment. The genotypes G23, G8 and G15 were the winners in this mega-environment.