Northern Grain Research Articles

Quantifying the resistance of Australian wheat genotypes to Pratylenchus thornei based on a continuous metric from a factor analytic linear mixed model

Genetic resistance to the parasitic root-lesion nematode, Pratylenchus thornei, is one of the main management strategies cereal growers can use to minimise the impact of nematodes on winter cereal cropping. Screening of genotypes in the presence of P. thornei populations must provide reliable resistance measures that are realised under field conditions. Adoption of the latest statistical methodologies can help to better differentiate between resistant and susceptible genotypes. In this study, post-harvest P. thornei population densities were measured from a collection of 17 field experiments, with varying starting P. thornei population densities, conducted between 2011 and 2018 in locations across the northern grain growing region of eastern Australia. The experiments primarily consisted of wheat genotypes. The post-harvest P. thornei population densities were analysed across multiple environments in a linear mixed model framework, with a factor analytic structure used to model genotype by environment (G ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} E) interaction effects exclusively for wheat genotypes. In general, genetic correlations between environments were found to be high, indicating limited G ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} E interaction for resistance to P. thornei. Post-processing of results using the factor analytic selection tools (FAST) method provided a measure of the overall performance for each wheat genotype, as well as a stability measure reflecting the consistency of the resistance status across environments. The FAST method quantified genotype resistance on a continuous scale, better reflecting the nature of genetic resistance based on a quantitative variable such as nematode population density, and provided a statistically robust and informative means of aiding selection decisions for resistance to P. thornei.

Drought Stress Affects the Reproductive Biology of Avena sterilis ssp. ludoviciana

Avena sterilis ssp. ludoviciana (hereafter, A. ludoviciana) is considered the most difficult-to-control winter weed in the Northern Grains Region (NGR) of Australia. The abundance of this weed has increased after the adoption of the no-tillage conservation agriculture (NTCA) approach, which does not bury seeds deep in the soil profile. In addition, the increasing frequency and intensity of drought stress events during the late winter to early spring period in the NGR may modify this weed’s persistence mechanisms, which may further impact crop production. The present study focused on plant maturity time and seed production, dormancy, and longevity of four NGR A. ludoviciana biotypes in relation to the severity of drought stress over 2 consecutive years. Plants of all four A. ludoviciana biotypes were grown under 100% plant available water capacity (PAWC) until panicle initiation. At panicle initiation, very mild (80% PAWC), mild (60% PAWC), moderate (40% PAWC), and severe (20% PAWC) drought stresses were imposed on plants and continued through to maturity; an additional subset of plants were maintained at 100% PAWC through to maturity (control). Plants exposed to severe drought stress matured 24 days earlier than control plants, and produced 34% fewer filled seeds, with seeds having a 42% lower mass, 70% less dormancy, and shorter predicted longevity of at least 2 years compared to the seeds produced on control plants. All reproductive traits were less affected when the severity of the drought stress was decreased. The increasing frequency of drought stress in combination with the widely adopted practice of NTCA favours seeds of A. ludoviciana to undergo rapid germination in the following autumn/winter NGR planting season. However, effective control of A. ludoviciana remains a challenge in the NGR due to this weed’s genetic variability with respect to its response toward the seasonal variability of the NGR.

Herbicide Resistance in Summer Annual Weeds of Australia’s Northern Grains Region

For more than two decades, glyphosate has been relied on to control summer annual weeds in fallow systems in Australia’s northern grains region. With numerous cases of glyphosate resistance reported in weed species collected from this region, there are concerns about the future viability of this herbicide. A random seed collection survey of summer weeds was conducted between 2016 and 2018 with the aim of determining the frequency and distribution of resistance to glyphosate and other herbicides commonly used for summer weed control. Glyphosate resistance was ubiquitous in fleabane, with all collected populations resistant to this herbicide. Glyphosate resistance was also prevalent in feathertop Rhodes grass, windmill grass, and awnless barnyard grass, with resistance detected in 68%, 58%, and 36% of populations, respectively. Only 14% of sowthistle populations collected between 2013 and 2108 were resistant to glyphosate. Resistance to haloxyfop was detected in feathertop Rhodes grass, albeit at a low frequency (2%). Other herbicides, such as 2,4-D amine, propaquizafop, and clethodim, provided good control of the broadleaf and grass weeds tested. The results from these surveys conducted between 2013 and 2017 provide a first glimpse of the state of herbicide resistance in key crop weeds for Queensland and the northern region of New South Wales. It is clear that farmers and agronomists need to consider incorporating non-chemical weed management tactics to promote the sustainability of current herbicides.

Elevated Temperature Affects Avena sterilis ssp. ludoviciana Reproductive Biology

The weed Avena sterilis ssp. ludoviciana has a high economic impact in the winter cereal crop production systems of Australia’s northern grains region (NGR). In the NGR, the frequency of high-temperature periods at the end of winter is increasing. This shift in climate may modify this weed’s maturity time and reproductive biology, and thereby impact on crop production. This study examined the reproductive biology of four A. ludoviciana biotypes in relation to elevated temperature when applied at different times during their seed development. Plants of all four A. ludoviciana biotypes were grown in an ambient temperature glasshouse (23/14 °C day/night). At panicle initiation, a portion of the plants were transferred to an elevated temperature glasshouse (29/23 °C day/night) and remained there until maturity. This process of plant movement was repeated on three further occasions with separate batches of plants, each 10 days apart. The remaining plants were kept under ambient conditions for their whole lifespan. Plants exposed to elevated temperature from panicle initiation to maturity, matured 18 days earlier than plants kept under ambient conditions, had 30% fewer filled seeds, 37% lower seed mass, and 40% less seed dormancy. Depending on the time and duration of plants exposed to elevated temperature, predicted seed longevity was ranged from 1 to 4 years in the soil seedbank. All reproductive traits were less affected when plants were exposed to elevated temperature at a later stage of development. If the frequency of high-temperature periods continues to increase, then it may lead to the development of less dormant populations of this weed that would be ready to germinate and re-infest the next winter crops under no-tillage conservation agriculture (that does not bury seeds deep in the soil profile). However, the seasonal climatic variability of the NGR in addition to the weed’s natural genetic variability may contribute to a seedbank of both dormant and less dormant seeds—making this species an even more difficult-to-control weed.

Remote detection of Fusarium crown rot in broadacre bread wheat and durum wheat through use of aerial imagery

Context The cereal disease Fusarium crown rot (FCR), caused by the fungal pathogen Fusarium pseudograminearum, is a worldwide major constraint to winter cereal production, especially in Australia’s northern grain region of New South Wales and Queensland. Aims Detection of the disease is labour-intensive and often not spatially quantifiable; hence, the aim of this study was to provide methods for in-crop FCR detection on a broadacre scale. Methods A replicated field experiment across three locations in northern New South Wales explored the use of thermal and multispectral imagery and hyperspectral reflectance data for the spatial detection of FCR in three bread wheat (Triticum aestivum L.) and three durum wheat (T. durum Desf.) varieties in the presence and absence of inoculation with F. pseudograminearum. Key results Canopy temperature was 0.30–0.90°C higher in two-thirds of field sites inoculated with the pathogen during early wheat growth in a slightly wetter than normal season. Some multispectral indices including normalised difference red edge, normalised difference vegetation index, near infrared and red edge also demonstrated the ability to identify inoculated versus uninoculated treatments as early as the first node stage (GS31). Conclusions Although positive identification was achieved with remote detection, environmental conditions (i.e. soil-water availability and ambient temperature) and physiological maturity influenced the accuracy of the technology for detecting FCR infection, particularly in wetter early-season conditions. Implications Early spatial detection of FCR infection on a broadacre scale could allow producers to manage this disease spatially through better agronomic decisions.

Identification of environment similarities using a crop model to assist the cultivation and breeding of a new crop in a new region

Context Rainfed crop-growing environments are known for their high yield variability, especially in the subtropics and tropics. Improving the resilience of crops to such environments could be enhanced with breeding and agronomy research focusing on groups of similar environments. Aim This study presents a framework for developing these groups using the Agricultural Production Systems Simulator (APSIM, ver. 7.10) model. Methods As a case study, the framework was applied for pigeonpea (Cajanus cajan L. Millsp.) as a potential new pulse crop for the Australian northern grains region. The model was first validated and then used to simulate yield, compute heat and drought stress events and analyse their frequencies for 45 locations over 62 seasons from 1960 to 2021. Key results The model performed satisfactorily compared to field trial data for several sowing dates and locations. The simulated yield varied greatly across locations and seasons, with heat-stress events (maximum temperature ≥35°C) and rainfall showing highly significant associations with this variability. The study identified seven groups of locations after converting the simulated yield into percentiles, followed by clustering. Drought-and-heat stress patterns varied across these groups but less so within each group. Yield percentiles significantly declined over the seasons in three of the seven groups, likely due to changing climate. Conclusions The framework helped identify pigeonpea’s key production agroecological regions and the drought and heat constraints within each region. Implications The framework can be applied to other crops and regions to determine environmental similarity.

Pesticide extraction from soil into runoff under a rainfall simulator

Context Runoff estimation is an important aspect of pesticide environmental behaviour and is the major loss pathway to the environment. Aims To improve understanding of pesticide runoff. Methods Data from three rainfall simulator studies was used. Twelve pesticides were studied ranged from tightly sorbed (DDE, soil sorption coefficient (KD) ~15 000 L kg−1) to weakly sorbed (dimethoate, KD < 30). Key results Event runoff pesticide concentrations were closely related to soil concentrations (0–25 mm depth). The ratio of runoff to soil concentration (the runoff extraction ratio, ERO), was similar for pesticides with a wide range of sorption and across the three soils: runoff concentration (μg L−1) = 28 × soil concentration (mg kg−1). ERO decreased with time after spraying, presumably due to lower concentrations in the top few mm of soil. Conclusions This model provides improved or similar estimates of pesticide runoff than previous models. Similar ERO values between sites was probably due to similar hydrology (high rainfall intensity, surface sealing, moist subsoils) and erosion, and because the same masses of soil and water are involved in mixing. Reduction in runoff concentrations by leaching was not influential, because infiltration was small and soil sorption too high. Implications Conditions studied apply during summer storms on most cotton and grain land on clay soils in the northern grain and cotton lands in eastern Australia. The model should be applicable under these conditions.

Fusarium Crown Rot Reduces Water Use and Causes Yield Penalties in Wheat under Adequate and above Average Water Availability

The cereal disease Fusarium crown rot (FCR), caused by the fungal pathogen Fusarium pseudograminearum, is a worldwide major constraint to winter cereal production but especially in Australia’s northern grain’s region (NGR) of NSW and Queensland. Conventionally, FCR induced yield penalties are associated with semi-arid water-limited conditions during flowering and grain-filling. In this study, yield penalties associated with FCR infection were found to be significant under both adequate and above average water conditions which has implication for global wheat production in more favorable environments. This research was conducted to understand the impact of FCR on water availability, yield and grain quality in high protein bread and durum wheat varieties in controlled environment and replicated field experiments across three locations in the NGR over a two-year period. Under controlled conditions, FCR infection significantly decreased water use by 7.5% with an associated yield reduction of 9.5% irrespective of water treatment. Above average rainfall was experienced across all field experimental sites in both 2020 and 2021 growing seasons. The field studies demonstrated a decrease in water use of upwards of 23% at some sites and significant yield penalties across all cultivars of up to 18.4% in natural rainfed scenarios to still 13.2% with further supplementary irrigation.

The Weed-Suppressive Ability of Summer Cover Crops in the Northern Grains Region of Australia

Pressure is mounting on the agricultural sector to reduce reliance on herbicides for weed control leading to increased interest in the potential of cover crops to control weeds in summer fallows. The weed suppression ability of three summer cover crop species, buckwheat, millet and teff, was evaluated in field trials at two sites near Camden, NSW in 2021. Buckwheat, millet and teff reduced weed biomass by 65%, 77% and 95%, respectively at Bringelly and by 94%, 92% and 90%, respectively at Lansdowne. Following cover crop desiccation, teff residues reduced weed emergence in subsequently planted wheat by 73% and 26% at Bringelly and Lansdowne, respectively. Overall cover crops were found to be effective in suppressing weed emergence, growth, and reproductive capacity. These studies identified teff grass as an important summer crop option for the northern grains region.

Transcriptomic Analysis of Early Flowering Signals in 'Royal' Flax.

Canada is one of the world’s leading producers and exporters of flax seed, with most production occurring in the Prairie Provinces. However, reduced season length and risk of frost restricts production in the northern grain belt of the Canadian Prairies. To expand the growing region of flax and increase production in Canada, flax breeders need to develop earlier-flowering varieties capable of avoiding the risk of abiotic stress. A thorough understanding of flowering control of flax is essential for the efficient breeding of such lines. We identified 722 putative flax flowering genes that span all major flowering-time pathways. Frequently, we found multiple flax homologues for a single Arabidopsis flowering gene. We used RNA sequencing to quantify the expression of genes in the shoot apical meristem (SAM) at 10, 15, 19, and 29 days after planting (dap) using the ‘Royal’ cultivar. We observed the expression of 80% of putative flax flowering genes and the differential expression of only 30%; these included homologues of major flowering regulators, such as SOC1, FUL, and AP1. We also found enrichment of differentially expressed genes (DEGs) in transcription factor (TF) families involved in flowering. Finally, we identified the candidates’ novel flowering genes amongst the uncharacterized flax genes. Our transcriptomic dataset provides a useful resource for investigating the regulatory control of the transition to flowering in flax and for the breeding of northern-adapted varieties.

Germination behaviour of

Context Avena sterilis subsp. ludoviciana (wild oats) is one of the major winter weeds of the Northern Grains Region of Australia. The abundance of this weed increased dramatically after the adoption of no-tillage conservation agriculture (NTCA). However, information is lacking on the germination characteristics of the two types of seed (i.e. primary and secondary) that it produces. Aims We aimed to determine the light and temperature requirements for germination and the time to germination of primary and secondary seeds of A. ludoviciana, in order to find ways to manage this weed effectively under NTCA systems. Methods Primary and secondary seeds and caryopses from two southern and two northern biotypes were exposed to a range of temperature and light regimes in the glasshouse, and germination was assessed. Key results All biotypes had ∼25% higher germination from primary than secondary seeds. Removing the hull increased caryopsis germination by ∼70%. The use of a light/dark photoperiod stimulated germination of both types of seed and caryopses compared with continuous darkness. Based on data for caryopses, 7°C and 9°C were found to be optimal germination temperatures for southern and northern biotypes, respectively. At optimum germination temperature, primary caryopses germinated 7–20 days earlier than secondary caryopses. In addition, a light/dark environment resulted in germination 2–6 days earlier than continuous darkness. Conclusions In the Northern Grains Region, seeds retained on or close to the soil surface (i.e. in NTCA systems) can undergo maximum germination during May–June (late autumn–winter), when long-term average temperatures match optimum germination temperatures. This coincides with winter crop plantings. Implications The seasonal timing of germination and the difference in germination timing between primary and secondary seeds, which help to stagger emergence of this weed, are major issues that need to be addressed in NTCA systems.

Northern grain and the Flemish nation in Genoa: the structural consequences of a famine (1585–1616)

This article is a case study in the formation and function of commercial networks in the early Modern Period. Analysing the network structures and strategies of foreign businessmen in urban contexts, the inquiry focuses on the Republic of Genoa’s role in the grain trade during the 16th and the 17th centuries. To do so, it examines the contributions of ‘Northern’ merchants in the creation of new commercial networks on a European scale during a major famine. The crisis forced the Republic to open new supply channels, towards Northern Europe and the Baltic region. Through their correspondents abroad, Northern European traders were urged to send grains and agents to Genoa. They did, and the numbers and the prestige of the German and the Flemish nations in the city increased. Their presence changed the commercial networks of the Genoese victualling institution, the Magistrato dell’Abbondanza, and they gained considerable influence after the famine.

Phenotyping for Waterlogging Tolerance as a Proxy for Phytophthora medicaginis Resistance in Chickpea

Phytophthora root rot (PRR) caused by the soilborne oomycete Phytophthora medicaginis is a significant constraint to chickpea (Cicer arietinum) production across the northern grains region of Australia. In flooded soil, which is conducive to PRR disease development, up to 70% yield loss can occur in the most resistant Australian cultivars. Incorporating waterlogging tolerance in soybean (Glycine max) has been shown to improve quantitative resistance to Phytophthora sojae. Root growth of three chickpea genotypes was assessed at the seedling stage under waterlogging, PRR, and the combination of these abiotic and biotic constraints. Levels of waterlogging tolerance in chickpea are inherently low, yet selected genotypes displayed variability in root traits linked to improved waterlogging tolerance. The PRR moderately susceptible chickpea cultivar Yorker and PRR very susceptible Rupali demonstrated an eightfold increase in early adventitious root growth from the epicotyl region under waterlogging stress, compared with the PRR resistant interspecific backcross genotype 04067-81-2-1-1 (C. echinospermum × C. arietinum*2). Selection for primary root depth, which was significantly greater in 04067-81-2-1-1 under waterlogging, appears to improve PRR resistance compared with root replacement traits. Soilborne Phytophthora spp. are reportedly attracted to branch sites and leached exudates. We propose that compromised root barriers at emergence sites of adventitious roots under waterlogging conditions hasten hyphal entry, potentially increasing susceptibility to PRR. Hence, screening for root depth and absence of adventitious root development under waterlogged conditions may offer a novel proxy phenotyping method for PRR resistance traits at early stages of chickpea breeding.

Effect of emergence time on growth and fecundity of Rapistrum rugosum and Brassica tournefortii in the northern region of Australia

Weeds from Brassicaceae family are a major threat in many crops including canola, chickpea, cotton and wheat. Rapistrum rugosum (L) All. and Brassica tournefortii Gouan. are two troublesome weeds in the northern region of Australia. In order to examine their phenology of these weeds, a pot study was conducted in 2018 at the Research Farm of the University of Queensland, Gatton campus with two populations sourced from high (Gatton) and medium (St George) rainfall areas of the northern grain region of Australia. Planting was carried out monthly from April to September, and the growth, flowering and seed production were evaluated. Maximum growth and seed production were observed in weeds planted in April, compared to other planting dates. Biomass of R. rugosum and B. tournefortii was reduced by 85% and 78%, respectively, as a result of the delay in planting from April to July. R. rugosum and B. tournefortii produced more than 13,000 and 3500 seeds plant−1, respectively, when planted in April and seed production was reduced by > 84% and > 76% when planted in July. No significant differences were observed between populations of both weeds for plant height, number of leaves and biomass, however, the medium rainfall population of R. rugosum produced more seeds than the high rainfall population when planted in April. The results of this study suggest that, although R. rugosum and B. tournefortii were able to emerge in a wider time frame, the growth and seed production were greatest when both weeds were planted in April and there was concomitant reduction in growth attributes when planted in the subsequent months, indicating that management of these weeds early in the cropping season is a prerequisite to population reduction and the mitigation of crop yield losses.

Insights into the value of seasonal climate forecasts to agriculture

Seasonal climate forecasts (forecasts) aim to reduce climate‐related productivity risk by helping farmers make decisions that minimise losses in poor years and maximise profits in good years. Most Australian forecast valuations have focused on fertiliser decisions to wheat operations, and few assessments have evaluated the benefit of incremental improvements of forecast skill. These gaps have limited our understanding of forecast value to the broader agriculture sector and the benefit of investments to improve forecast skill. To address these gaps, we consistently assessed forecast value for seven Australian case studies (southern grains, northern grains, southern beef, northern beef, lamb, cotton, and sugar). We implemented a three‐stage methodology which consisted of engagement with industry practitioners; modelling production under different climatic and environmental conditions; and economic modelling to evaluate forecast value for eleven levels of forecast skill. Our results show that forecast value was often low and highly variable. Value was found to vary based on forecast attributes (forecast skill, resolution and state), industry application and prevailing conditions (environmental and market). This is the first Australian valuation study where the same methodological approach was applied across multiple industries, incremental improvements in skill were valued, and prevailing conditions were explicitly evaluated for impact on value.

Combining Fractional Cover Images with One-Class Classifiers Enables Near Real-Time Monitoring of Fallows in the Northern Grains Region of Australia

Fallows are widespread in dryland cropping systems. However, timely information about their spatial extent and location remains scarce. To overcome this lack of information, we propose to classify fractional cover data from Sentinel-2 with biased support vector machines. Fractional cover images describe the land surface in intuitive, biophysical terms, which reduces the spectral variability within the fallow class. Biased support vector machines are a type of one-class classifiers that require labelled data for the class of interest and unlabelled data for the other classes. They allow us to extrapolate in-situ observations collected during flowering to the rest of the growing season to generate large training data sets, thereby reducing the data collection requirements. We tested this approach to monitor fallows in the northern grains region of Australia and showed that the seasonal fallow extent can be mapped with >92% accuracy both during the summer and winter seasons. The summer fallow extent can be accurately mapped as early as mid-December (1–4 months before harvest). The winter fallow extent can be accurately mapped from mid-August (2–4 months before harvest). Our method also detected emergence dates successfully, indicating the near real-time accuracy of our method. We estimated that the extent of fallow fields across the northern grains region of Australia ranged between 50% in winter 2017 and 85% in winter 2019. Our method is scalable, sensor independent and economical to run. As such, it lays the foundations for reconstructing and monitoring the cropping dynamics in Australia.

Frost Risk Management in Chickpea Using a Modelling Approach

Post-flowering frosts cause appreciable losses to the Australian chickpea industry. The Northern Grains Region (NGR) of Australia, which accounts for nearly 95% of chickpea production in Australia, is frequently subjected to such events. The objective of this study was to map frost risk in chickpea in the NGR and develop strategies to minimise the impacts of such risk. The Agricultural Production System Simulator (APSIM) modelling framework was used to determine spatial and temporal trends in post-flowering frost risk. The NGR could be divided into six broad sub-regions, each delineating locations with similar frost risk. The risk was nearly two to three times greater in the Southern Downs and Darling Downs sub-regions as compared to the Central Queensland Highlands, Dawson Callide, New South Wales, and Northern New South Wales–Western Downs sub-regions. There was an increasing trend in the frequency of frost events in the Southern Downs and New South Wales sub-regions, and a decreasing trend in the Central Queensland Highlands and Dawson Callide sub-regions, consistent with the changing climate of the NGR. In each sub-region, frost risk declined with delayed sowings, but such sowings resulted in simulation of reduced water limited yield potential (unfrosted) as well. The model output was also used to compute 10, 30, 50, and 70% probabilities of the last day of experiencing −3 to 2 °C minimum temperatures and identify the earliest possible sowings that would avoid such temperatures after flowering. Choosing the earliest sowing times with a 30% frost risk could help increase overall yields in environments with high frost risk. Simulations involving genotype x environment x management interactions suggested additional opportunities to minimise frost losses through the adoption of particular cultivars of differing phenology and the use of different agronomy in various environments of the NGR. The study indicates that there is considerable variation in frost risk across the NGR and that manipulating flowering times either through time of sowing or cultivar choice could assist in minimising yield losses in chickpea due to frost.

Growth behavior and glyphosate resistance level in 10 populations of Echinochloa colona in Australia.

Recently, poor control of Echinochloa colona with glyphosate has been reported in no-till agriculture systems of the northern grain region (NGR) of Australia. Two experiments were conducted using 10 populations of E. colona selected from the NGR of Australia to understand differences in their growth behavior and resistance pattern. Growth studies revealed that these populations differed in plant height (53-70 cm plant-1), tiller production (30-52 tillers plant-1), leaf production (124-186 leaves plant-1) and seed head production (37-65 seed heads plant-1). Days taken to seed heads and shoot biomass in these populations ranged between 40-48 d and 21-27 g plant-1, respectively. Seed production in these populations ranged between 5380 and 10244 seeds plant-1; lowest for population B17/25 and highest for population B17/13. Correlation studies revealed that seed number plant-1 had a positive correlation with tiller number plant-1 (r = 0.73) and negative relation with days taken to seed head initiation (r = - 0.65). The glyphosate dose-response study showed a wide range of responses in these populations and the glyphosate dose required to kill 50% plants (LD50 values) was estimated between 161 to 2339 g a.e. glyphosate ha-1. LD50 values of populations B17/16, B 17/34 and B17/35 were 1086, 2339 and 1153 g ha-1, respectively, making them 6.7, 15.1 and 7.2-fold resistant to glyphosate compared with the susceptible population B17/37. Growth behavior and seed production potential in these populations had no correlation with the resistance index. These results suggest that some populations of E. colona are highly problematic; for example, population B17/34 was not only highly glyphosate-resistant, but also produced a high seed number (9300 seeds plant-1). This study demonstrated that there is a possibility of great risk with the increased use of glyphosate for managing E. colona in the NGR of Australia. The results warrant integrated weed management strategies and improved stewardship guidelines are required for managing glyphosate-resistant populations of E. colona and to restrict further movement of resistant populations to other regions of Australia.

Biology of Brassica tournefortii in the northern grains region of Australia

Brassica tournefortii Gouan. (wild turnip, WT) has become a problematic weed in the no-till production systems of the northern grains region of Australia. Experiments were undertaken using different biotypes of B. tournefortii to examine its phenology, emergence and seedbank persistence. Biotypes were obtained from paddocks of barley (Hordeum vulgare L.) (WT1 and WT9) and chickpea (Cicer arietinum L.) (WT1/17 and WT2/17). Fresh seeds initially had high dormancy rates and persisted for a short period on the surface. Seedbank persistence increased with burial depth, with 39% of seeds remaining for WT1 and 5% for WT9 after 30 months at 2 cm depth. Persistence of buried seeds varied across biotypes; WT1/17 seedlings also emerged in the second growing season from 2 cm depth. Compared with buried seeds, seedlings readily emerged from the surface (in March–June following increased rainfall) within 6 months of planting. Emergence was greatest on the surface and varied between biotypes and tillage systems; the highest rate recorded was ~14%. Multiple cohorts were produced between February and October. No-till systems produced higher emergence rates than conventional tillage systems. Seedlings of B. tournefortii did not emerge from 5 cm soil depth; therefore, diligent tillage practices without seedbank replenishment could rapidly reduce the presence of this weed. A soil-moisture study revealed that at 25% of water-holding capacity, B. tournefortii tended to produce sufficient seeds for reinfestation in the field. Brassica tournefortii is a cross-pollinated species, and its wider emergence time and capacity to produce enough seeds in a dry environment enable it to become widespread in Australia. Early cohorts (March) tended to have vigorous growth and high reproduction potential. This study found B. tournefortii to be a poor competitor of wheat (Triticum aestivum L.), having greater capacity to compete with the slow-growing crop chickpea. Therefore, control of early-season cohorts and use of rotations with a more vigorous crop such as wheat may reduce the seedbank. The information gained in this study will be important in developing better understanding of seed ecology of B. tournefortii for the purpose of developing integrated management strategies.

Emergence and germination response of Sonchus oleraceus and Rapistrum rugosum to different temperatures and moisture stress regimes

AbstractSonchus oleraceus and Rapistrum rugosum are two rapidly emerging weeds of the northern grain region of Australia. To understand the ability of these weeds regarding their germination response to temperature and different soil moisture regimes, experiments were undertaken on the germination of these weeds at varying osmotic potential and temperature regimes. The experiment was conducted as a split‐plot design with alternating day/night temperature regimes (15/5, 20/10, 25/15 and 30/20°C) as a main plot and osmotic potential regimes (0.0, −0.1, −0.2, −0.4, −0.6, −0.8 and −1 MPa) as a subplot. At different temperature regimes, there was 65–91% germination of S. oleraceus in water (0 MPa). There was 0–4% germination at −0.8 MPa and no germination at −1.0 MPa. Osmotic potential values that can cause 50% reduction in germination of S. oleraceus based on a sigmoid regression model ranged from −0.38 to −0.48 MPa. There was 33–81% germination of R. rugosum in distilled water (0 MPa), 1–3% germination at −0.8 MPa and no germination at −1.0 MPa. Osmotic potential values that can cause 50% reduction in germination of R. rugosum based on a sigmoid model ranged from −0.26 to −0.54 MPa. Results of the study were related to the emergence pattern of weeds during field survey and soil moisture profiles estimated by the Australian Landscape Water Balance Model and explain the emergence of these weeds outside the normal seasonal window of prevalence as a response to changes in weather.