Northern Grain Research Articles

Pratylenchus thornei populations reduce water uptake in intolerant wheat cultivars

Pratylenchus thornei is a major pathogen of wheat crops in the northern grain region of Eastern Australia with an estimated annual yield loss of $38 million. Damaged crops show symptoms of water and nutrient stress that suggest uptake is significantly affected. In order to understand the mechanisms involved in reducing water uptake and consequently plant yield, detailed measurements of water extraction and leaf area were conducted on a range of wheat cultivars with differing levels of tolerance and resistance to P. thornei.Planting wheat into high populations of P. thornei reduced the extraction rate (kl) in the intolerant cultivars; this in turn caused a delay in the root extraction velocity and effectively changed the crop lower limit. The early season stress applied by the reduced extraction rate impeded canopy development that consequently reduced demand for water and nutrients, growth and yield potential. The resulting yield loss was consistent across both a wet and a dry wheat growing season with the intolerant cultivar yielding 34% less than the tolerant cultivar. Understanding the mechanism with which P. thornei reduces yield allows the impact of P. thornei to be included in simulation models to better understand how to manage this constraint to the Australian grain industry.

Ammonia volatilisation from nitrogen fertilisers surface-applied to bare fallows, wheat crops and perennial-grass-based pastures on Vertosols

Farmers on Vertosols in the northern grains region of Australia are increasingly using pre-crop broadcasting and in-crop topdressing of nitrogen (N) fertilisers. Surface application risks gaseous loss via ammonia volatilisation, but the magnitude of N loss is unknown. Because both soil properties and environmental conditions influence ammonia volatilisation, measurements need to be field-based and non-intrusive, e.g. micrometeorological. We used an integrated horizontal flux technique to measure ammonia volatilised from neutral to alkaline Vertosols for a month after the application of several fertiliser products in 10 bare-fallow paddocks, seven mid-tillering wheat crops, and two perennial-grass-based pastures. Ammonia loss from urea averaged 11% (5.4–19%) when applied to fallow paddocks, 4.8% (3.1–7.6%) when applied to wheat, and 27% when applied to pasture. Volatilisation from urea applied to pastures was high, because there was little rain after spreading. Losses from ammonium sulfate applied to pastures were >60% less than from urea. Nitrogen losses from ammonium sulfate were high (18.6–33.8%) from soils with >10 g 100 g–1 of calcium carbonate (CaCO3), but were 52% less than from urea at five of eight fallow paddocks on non-calcareous soils, and 76% less than from urea at the two pasture paddocks. Coating urea with N-(n-butyl)thiophosphoric triamide reduced ammonia loss at just two of eight fallow paddocks and one of three in-crop paddocks. Ammonia volatilisation from aqueous solutions of urea, urea ammonium nitrate, and ammonium nitrate were either less than or no different from losses from granulated urea, but not consistent. With the exception of ammonium sulfate applied to soils with >10 g 100 g–1 of CaCO3, surface application of N fertiliser during autumn–winter on cropped Vertosols in the Australian northern grains region does not lead to major N loss via ammonia volatilisation.

Corrigendum to: Crop-available water and agronomic management, rather than nitrogen supply, primarily determine grain yield of commercial chickpea in northern New South Wales

Chickpea (Cicer arietinum L.) is considered an effective rotation crop in Australia's northern grains region; however, concerns exist that grain yields of commercial crops are reduced because of nitrogen (N) deficiency related to inadequate nodulation and N2 fixation. As part of a program to address these issues, we report on the monitoring of 22 commercial fields around Moree, northern NSW, during 2005–07 that were designated for chickpea, and an associated farmer survey (81 respondents). Our objectives were to determine whether the monitored crops were limited by N and to develop recommendations that would optimise productivity for farmers growing chickpeas. In 2005, only soil water and nitrate data were collected from the six fields designated for chickpea. In 2006 and 2007, almost complete datasets were assembled from the 16 chickpea fields or crops, including soil water and nitrate at sowing, row spacing, plant density, plant height, stubble cover, weed density and composition, shoot biomass, grain yield, nodulation and N2 fixation (%N derived from the atmosphere (%Ndfa) and total crop N fixed). The associated survey provided insights into farmer knowledge of, and practices related to, inoculation. Field monitoring indicated moderate–high levels of soil nitrate at sowing (averages 114, 126 and 110kg N ha–1 to 1.2m depth for 2005, 2006 and 2007, respectively) and generally low plant nodulation (0.11–1.16g fresh wt plant–1) and N2 fixation (0–62%Ndfa and 0–87kg N ha–1). Grain yield varied between 0.53 and 2.91tha–1 across the 14 monitored crops, with averages of 1.89tha–1 in 2006 and 1.02tha–1 in 2007. Although total crop N and grain yields were highly correlated with total (i.e. soil+fixed) N supply, there was no evidence that the monitored chickpea crops were N-limited. Rather, we conclude that soil N and biologically fixed N were complementary in supplying N to the crops, the grain yields of which were primarily determined by the supply of plant-available water (PAW) and water-use efficiency (WUE). Simple and multivariate regression analyses showed that stubble cover during the fallow (positively correlated with sowing PAW) and sowing date (positively correlated with crop WUE) were significant determinants of grain yield. We conclude that farmers could improve inoculation practice by ensuring the time between seed inoculation and sowing is always

Wheat biomass and yield increased when populations of the root-lesion nematode (Pratylenchus thornei) were reduced through sequential rotation of partially resistant winter and summer crops

The root-lesion nematode, Pratylenchus thornei, can reduce wheat yields by >50%. Although this nematode has a broad host range, crop rotation can be an effective tool for its management if the host status of crops and cultivars is known. The summer crops grown in the northern grain region of Australia are poorly characterised for their resistance to P. thornei and their role in crop sequencing to improve wheat yields. In a 4-year field experiment, we prepared plots with high or low populations of P. thornei by growing susceptible wheat or partially resistant canaryseed (Phalaris canariensis); after an 11-month, weed-free fallow, several cultivars of eight summer crops were grown. Following another 15-month, weed-free fallow, P. thornei-intolerant wheat cv. Strzelecki was grown. Populations of P. thornei were determined to 150 cm soil depth throughout the experiment. When two partially resistant crops were grown in succession, e.g. canaryseed followed by panicum (Setaria italica), P. thornei populations were <739/kg soil and subsequent wheat yields were 3245 kg/ha. In contrast, after two susceptible crops, e.g. wheat followed by soybean, P. thornei populations were 10 850/kg soil and subsequent wheat yields were just 1383 kg/ha. Regression analysis showed a linear, negative response of wheat biomass and grain yield with increasing P. thornei populations and a predicted loss of 77% for biomass and 62% for grain yield. The best predictor of wheat yield loss was P. thornei populations at 0–90 cm soil depth. Crop rotation can be used to reduce P. thornei populations and increase wheat yield, with greatest gains being made following two partially resistant crops grown sequentially.

Dilute Acid Extraction is a useful Indicator of the Supply of Slowly Available Phosphorus in Vertisols

Long-term studies suggest readily available P, measured using a bicarbonate extractant, can be replenished by slowly available inorganic P pools. The aim of this study was to estimate the supply of slowly available P to the soil solution. Readily and slowly available P pools were measured using two agronomic soil P tests (the bicarbonate (Colwell) and dilute acid (Bureau of Sugar Experiment Stations; BSES) extractants, respectively) in vertisol soils of the northern grains region (NGR) of eastern Australia. The amount of P supplied to the soil solution was estimated by the iron oxide sink method accumulated over 96 h (FeOt-P). The readily available P pool (i.e., Colwell-P) was strongly correlated with FeOt-P, and this pool was likely to be replenished by the slowly available P pool (i.e., BSES-P) when BSES-P concentrations were <61 mg P kg . The slowly available P pool did not supply the readily available P pool when the Ca (mg kg )/P (mg kg ) ratio in the BSES extract was <74:1, suggesting the presence of Ca phosphates of low solubility affected potential buffering. Using a multiple linear regression, approximately 75% of the variability in the ability of the slowly available P pool to supply soil solution P could be explained by the quantity of BSES-P and the ratio of Ca/P in the BSES extract.

Crop-available water and agronomic management, rather than nitrogen supply, primarily determine grain yield of commercial chickpea in northern New South Wales

Chickpea (Cicer arietinum L.) is considered an effective rotation crop in Australia’s northern grains region; however, concerns exist that grain yields of commercial crops are reduced because of nitrogen (N) deficiency related to inadequate nodulation and N2 fixation. As part of a program to address these issues, we report on the monitoring of 22 commercial fields around Moree, northern NSW, during 2005–07 that were designated for chickpea, and an associated farmer survey (81 respondents). Our objectives were to determine whether the monitored crops were limited by N and to develop recommendations that would optimise productivity for farmers growing chickpeas. In 2005, only soil water and nitrate data were collected from the six fields designated for chickpea. In 2006 and 2007, almost complete datasets were assembled from the 16 chickpea fields or crops, including soil water and nitrate at sowing, row spacing, plant density, plant height, stubble cover, weed density and composition, shoot biomass, grain yield, nodulation and N2 fixation (%N derived from the atmosphere (%Ndfa) and total crop N fixed). The associated survey provided insights into farmer knowledge of, and practices related to, inoculation. Field monitoring indicated moderate–high levels of soil nitrate at sowing (averages 114, 126 and 110 kg N ha–1 to 1.2 m depth for 2005, 2006 and 2007, respectively) and generally low plant nodulation (0.11–1.16 g fresh wt plant–1) and N2 fixation (0–62%Ndfa and 0–87 kg N ha–1). Grain yield varied between 0.53 and 2.91 t ha–1 across the 14 monitored crops, with averages of 1.89 t ha–1 in 2006 and 1.02 t ha–1 in 2007. Although total crop N and grain yields were highly correlated with total (i.e. soil + fixed) N supply, there was no evidence that the monitored chickpea crops were N-limited. Rather, we conclude that soil N and biologically fixed N were complementary in supplying N to the crops, the grain yields of which were primarily determined by the supply of plant-available water (PAW) and water-use efficiency (WUE). Simple and multivariate regression analyses showed that stubble cover during the fallow (positively correlated with sowing PAW) and sowing date (positively correlated with crop WUE) were significant determinants of grain yield. We conclude that farmers could improve inoculation practice by ensuring the time between seed inoculation and sowing is always &lt;24 h.

Yield response in chickpea cultivars and wheat following crop rotations affecting population densities of Pratylenchus thornei and arbuscular mycorrhizal fungi

In Australia, root-lesion nematode (RLN; Pratylenchus thornei) significantly reduces chickpea and wheat yields. Yield losses from RLN have been determined through use of nematicide; however, nematicide does not control nematodes in Vertosol subsoils in Australia’s northern grains region. The alternative strategy of assessing yield response, by using crop rotation with resistant and susceptible crops to manipulate nematode populations, is poorly documented for chickpea. Our research tested the effectiveness of crop rotation and nematicide against P. thornei populations for assessing yield loss in chickpea. First-year field plots included canola, linseed, canaryseed, wheat and a fallow treatment, all with and without the nematicide aldicarb. The following year, aldicarb was reapplied and plots were re-cropped with four chickpea cultivars and one intolerant wheat cultivar. Highest P. thornei populations were after wheat, at 0.45–0.6 m soil depth. Aldicarb was effective to just 0.3 m for wheat and 0.45 m for other crops, and increased subsequent crop grain yield by only 6%. Canola, linseed and fallow treatments reduced P. thornei populations, but low mycorrhizal spore levels in the soil after canola and fallow treatments were associated with low chickpea yield. Canaryseed kept P. thornei populations low throughout the soil profile and maintained mycorrhizal spore densities, resulting in grain yield increases of up to 25% for chickpea cultivars and 55% for wheat when pre-cropped with canaryseed compared with wheat. Tolerance indices for chickpeas based on yield differences after paired wheat and canaryseed plots ranged from 80% for cv. Tyson to 95% for cv. Lasseter and this strategy is recommended for future use in assessing tolerance.

Modelling the behaviour of crown rot in wheat caused by Fusarium pseudograminearum

Existing spatiotemporal models for disease progress are unsuitable for describing epidemics of residue-borne diseases of cereals like crown rot, caused by Fusarium pseudograminearum, which increase in incidence over successive years and where inoculum has a fixed location. Monte Carlo simulation was used to explore the behaviour of a simple mechanistic model for crown rot, in which inoculum from each infected plant in one season came into contact with a defined number of plants in the following season. Contacted plants became infected according to a probability of infection that was less than 1. Growth chamber experiments confirmed that contact between infested residue and plants was required for infection. Observed features of epidemics at a long term trial site, including disease progress and maximum incidence, were satisfactorily fitted by simulations with a starting incidence of 4 %, 12 plants contacted by inoculum from each infected plant, and probability of infection of 0.66. This confirms that our understanding of disease behaviour at moderate to high levels of incidence is basically correct. However, infection rate between seasons was sensitive to initial incidence, suggesting that dispersal methods such as ascospores or conidia may be important at low incidence. A simple descriptive model was developed for the disease in bread wheat in the northern grains region of eastern Australia. Inoculum potential was estimated from the square root of the product of crown rot incidence and yield (a surrogate for biomass) of the preceding crop. Incidence of disease was related to inoculum potential by an infection constant. Crown rot inoculum was assumed to decline exponentially with time between susceptible crops. These two relationships were combined to predict the behaviour of the disease in different rotation systems. Over time, crown rot incidence converged to an equilibrium level that was determined by the infection constant, average yield, and the survival rate of inoculum. Modelled epidemics behaved in a way that was consistent with field data for continuous wheat, wheat-chickpea and wheat-sorghum rotations. This descriptive model could be used in extension or as a way of understanding how management and environment affect the disease.

Growth and phosphorus uptake of faba bean and cotton are related to Colwell-P concentrations in the subsoil of Vertosols

Recent studies report low and variable phosphorus (P) fertiliser use efficiency (PUE) for cotton in the northern grains region (NGR) of eastern Australia. This may be due to cotton accessing P pools that are not currently tested for in the subsoil (10–30 cm) or variation in response to P source and placement strategy. Two glasshouse studies were used to investigate this, incorporating two soil P tests to assess readily and slowly available P pools (Colwell, and a dilute acid colloquially referred to as the BSES extractant), and five different P fertiliser placement strategies in the subsoil. Eighteen Vertosols were collected across southern to central Queensland in the NGR, and then used to grow faba bean (Vicia faba L.) and cotton (Gossypium hirsutum L.) sequentially in the same 28-L pot. Readily available P pools assessed by Colwell-P were of major importance for faba bean and cotton dry matter, as well as for tissue P concentrations. Cotton was less responsive to extractable subsoil P concentrations than faba bean, suggesting either greater internal PUE or improved ability to accumulate P under conditions of limited availability. We recommend that subsoil P fertilisation should occur before sowing faba bean to maximise PUE in a cotton–faba bean rotation. Faba bean and cotton both recovered more P when the subsoil was fertilised, but no individual P fertiliser placement strategy was superior. Phosphorus extracted using the BSES method was not correlated with faba bean or cotton dry matter or tissue P concentration over the single crop cycle. We also recommend that Colwell-P be measured in the topsoil and subsoil to understand the quantity of plant-available P in Vertosols of the NGR, and that further research is needed to describe the resupply of the readily available P pool from slowly available P pools during a single crop cycle.

LOCALIZED SEPTORIA LEAF BLOTCH LESIONS IN WINTER WHEAT FLAG LEAF DO NOT ACCELERATE APICAL SENESCENCE DURING THE NECROTROPHIC STAGE

Mycosphaerella graminicola, the most damaging disease of wheat in Northern Europe, induces yield or grain quality losses usually related to green area losses. This work aims at clarifying whether induced senescence is due to an acceleration of apical senescence and thus to a modification of the leaf nitrogen remobilization rate. The effect on apical leaf senescence of a restricted diseased leaf area was investigated. The experiment involved four winter wheat cultivars varying in their susceptibility to four M. graminicola isolates. Flag leaves were inoculated at a dose representative of field epidemics. As soon as symptoms appeared, dynamics of apical senescence (Sapi) and around the inoculation zone (Ssep) were measured by repeatedly taking digital photos until senescent areas merged. Ssep trends were fit to a logistic function whose parameters depended on cultivar×isolate interactions. Disease severities ranged from 0 to 24% total leaf area. Apical senescence followed an exponential pattern in control and inoculated leaves. Sapi was twice as great in inoculated shoots as in controls, even when no disease occurred. The relative rate of Sapi depended on the cultivar, but no isolate effect was detected despite wide variations in Ssep extent. Paired comparisons between inoculated and control leaves showed that the relative rate of Sapi was not increased by inoculation. It is concluded, that over a wide range of Septoria disease, apical senescence was not accelerated in inoculated leaves as compared to control. Results suggest that the disease did not modify the regulation of leaf N remobilization rate.

Rediscovering the Virgin Lands: Agricultural Investment and Rural Livelihoods in a Eurasian Frontier Area

Summary Against the global debate on socially responsible agro-investment, we explore the conditions, patterns, and impacts of recent agricultural recovery in Kazakhstan’s northern grain provinces. Vertically and horizontally integrated agroholdings brought outside investment and management to this region. With stable employment in agriculture, real consumption spending of rural households has doubled within an 8-year period. Due to the socialist tradition of industrialized farming operations, rural inhabitants regard themselves primarily as workers and not as land owners. We conclude that investment in large-scale farming can provide benefits to rural people even with less than ideal-type political representation.

Stunted cotton (Gossypium hirsutum L.) fully recovers biomass and yield of seed cotton after delayed root inoculation with spores of an arbuscular mycorrhizal fungus (Glomus mosseae)

In the northern grain and cotton region of Australia, poor crop growth after long periods of fallow, called ‘long-fallow’ disorder, is caused by a decline of natural arbuscular-mycorrhizal fungi (AMF). When cotton was grown in large pots containing 22 kg of Vertisol from a field recently harvested from cotton in Central Queensland, plants in pasteurised soil were extremely stunted compared with plants in unpasteurised soil. We tested the hypothesis that this extreme stunting was caused by the absence of AMF and examined whether such stunted plants could recover from subsequent treatment with AMF spores and/or P fertiliser. At 42 days after sowing, the healthy cotton growing in unpasteurised soil had 48% of its root-length colonised with AMF, whereas the stunted cotton had none. After inoculation with AMF spores (6 spores/g soil of Glomus mosseae) and/or application of P fertiliser (50 mg P/kg soil) at 45 days after sowing, the stunted plants commenced to improve about 25 days after treatment, and continued until their total dry matter and seed cotton production equalled that of plants growing in unpasteurised soil with natural AMF. In contrast, non-mycorrhizal cotton grown without P fertiliser remained stunted throughout and produced no bolls and only 1% of the biomass of mycorrhizal cotton. Even with the addition of P fertiliser, non-mycorrhizal cotton produced only 64% of the biomass and 58% of the seed cotton (lint + seed) of mycorrhizal cotton plants. These results show that cotton is highly dependent on AMF for P nutrition and growth in Vertisol (even with high rates of P fertiliser), but can recover from complete lack of AMF and consequent stunting during at least the first 45 days of growth when treated with AMF spores and/or P fertiliser. This corroborates field observations in the northern region that cotton may recover from long-fallow disorder caused by low initial levels of AMF propagules in the soil as the AMF colonisation of its roots increases during the growing season.

PC-Based Automated Control System for Jordan Northern Grain Silo

This paper presents a PC-based automated control system operation of the Northern Grain Silo of Jordan. The system connects to a PLC (programmable logic controller) device, and combines operator interface, PLC programming and monitoring functions into one platform. The PLC portion handles direct operations control, while the PC portion handles interfacing and data intensive functions. A simulation package is developed. The package generates a graphical user interface for real-time graphic animations of the Grain Silo operation. We discuss anticipated benefits of such a system and phases of implementation.

Identification of anthracnose resistance in yellow lupin (Lupinus luteus L.) and its incorporation into breeding lines

With 3 tables Abstract Lupin anthracnose [caused by Colletotrichum lupini (Bondar) Nirenberg, Feiler & Hagedorn] first occurred in commercial crops in Western Australia (WA) in 1996 and severely affected the lupin industry, particularly in the northern grain belt of WA. Subsequent studies led to the identification of good sources of resistance to the disease in narrow-leafed lupin (Lupinus angustifolius L.) and white lupin (Lupinus albus L.). However, a reliable source of resistance was lacking in yellow lupin (Lupinus luteus L.) until recently. Screening of accessions obtained from various parts of the globe yielded three putative sources of resistance. Crosses were made between the resistant lines and other breeding lines. Consequently, several breeding lines have been developed with a partial resistance to the disease. This is the first report on the development of anthracnose resistance in yellow lupin. This level of resistance should provide enough protection to grow yellow lupin in southwest of WA as this region does not have blue lupin (Lupinus cosentinii Guss.), a perpetual natural host of the anthracnose pathogen.

Post head-emergence frost resistance of barley genotypes in the northern grain region of Australia

Post head-emergence frost causes substantial losses for Australian barley producers. Varieties with improved resistance would have a significant positive impact on Australian cropping enterprises. Five barley genotypes previously tested for reproductive frost resistance in southern Australia were tested, post head-emergence, in the northern grain region of Australia and compared with the typical northern control cultivars, Gilbert and Kaputar. All tested genotypes suffered severe damage to whole heads and stems at plant minimum temperatures less than −8°C. In 2003, 2004 and 2005, frost events reaching a plant minimum temperature of ~−6.5°C did not result in the complete loss of grain yield. Rather, partial seed set was observed. The control genotype, Gilbert, exhibited seed set that was greater than or equal to that of any genotype in each year, as did Kaputar when tested in 2005. Thus, Gilbert and Kaputar were at least as resistant as any tested genotype. This contrasts with trial results from the southern grain region where Gilbert was reported to be less resistant than Franklin, Amagi Nijo and Haruna Nijo. Hence, rankings for post head-emergence frost damage in the northern grain region differ from those previously reported. These results indicate that Franklin, Amagi Nijo and Haruna Nijo are not likely to provide useful sources of frost resistance or markers to develop improved varieties for the northern grain region of Australia.

Electromagnetic induction sensing of soil identifies constraints to the crop yields of north-eastern Australia

Salinity, sodicity, acidity, and phytotoxic concentrations of chloride (Cl–) in soil are major constraints to crop production in many soils of north-eastern Australia. Soil constraints vary both spatially across the landscape and vertically within the soil profile. Identification of the spatial variability of these constraints will allow farmers to tune management to the potential of the land, which will, in turn, bring economic benefit. For three cropping fields in Australia’s northern grains region, we used electromagnetic induction with an EM38, which measures apparent electrical conductivity of the soil (ECa) and soil sampling to identify potential management classes. Soil Cl– and soluble Na+ concentrations, EC of the saturated extract (ECse), and soil moisture were the principal determinants of the variation of ECa, measured both at the drained upper limit of moisture (UL) and at the lower limit (LL) of moisture extracted by the crop. Grain yield showed a strong negative relation with ECa at both UL and LL, although it was stronger for the latter. We arrive at a framework to estimate the monetary value of site-specific management options, through: (i) identification of potential management classes formed from ECa at LL; (ii) measurement of soil attributes generally associated with soil constraints in the region; (iii) grain yield monitoring; and (iv) simple on-farm experiments. Simple on-farm experiments suggested that, for constrained areas, matching fertiliser application to realistic yield potential, coupled to gypsum amelioration, could potentially benefit growers by AU$14–46/ha.year (fertiliser) and $207/ha.3 years (gypsum).

Inheritance of resistance to root-lesion nematode (Pratylenchus thornei) in wheat landraces and cultivars from the West Asia and North Africa (WANA) region

The root-lesion nematode Pratylenchus thornei causes substantial loss to bread wheat production in the northern grain region of Australia and other parts of the world. West Asia and North Africa (WANA) wheat accessions with partial resistance to P. thornei were analysed for mode of inheritance in a half-diallel crossing design of F1 hybrids (10 parents) and F2 populations (7 parents). General combining ability was more important than specific combining ability as indicated by components of variance ratios of 0.93 and 0.95 in diallel ANOVA of the F1 and F2 generations, respectively. General combining ability values of the ‘resistant’ parents were predictive of the mean nematode numbers of their progeny in crosses with the susceptible Australian cv. Janz at the F1 (R2 = 0.86, P &lt; 0.001, 8 crosses), F2 (R2 = 0.83, P &lt; 0.001, 9 populations) and F∞ (R2 = 0.71, P &lt; 0.05, 5 doubled-haploid populations). The F2 and F∞ populations showed relatively continuous distributions. Heritability was 0.68 for F2 populations in the half-diallel of resistant parents and 0.82–0.92 for 5 ‘resistant’ parent/Janz doubled-haploid populations (narrow-sense heritability on a line mean basis). The results indicate polygenic inheritance of P. thornei resistance with a minimum of from 2 to 6 genes involved in individual F∞ populations of 5 resistant parents crossed with Janz. Morocco 426 and Iraq 43 appear to be the best of the parents tested for breeding for resistance to P. thornei. None of the P. thornei-resistant WANA accessions was resistant to Pratylenchus neglectus.

Occurrence of root-lesion nematodes (Pratylenchus thorneiandP. neglectus) and stunt nematode (Merlinius brevidens) in the northern grain region of Australia

Pratylenchus thornei, P. neglectus and Merlinius brevidens were respectively present in soil from 67, 32 and 73% of 795 wheat fields sampled in the northern grain region of Australia. Population densities of P. thornei (31% of samples with >2000 nematodes/kg soil) were higher than those of P. neglectus (5%) or M. brevidens (11%). The mean proportion of plant-parasitic to total nematodes was 0.40. The incidence of P. thornei and P. neglectus increased significantly with the number of years that fields had been cropped since clearing natural vegetation. All three species occurred in soil samples across a wide range of texture and pH. Maximal incidence of P. thornei was in heavier textured soils (48% clay, 37% sand) than P. neglectus (39% clay,45%sand). The incidence of M. brevidens increased linearly with increasing clay and decreasing sand contents. M. brevidens occurred in the pH range 6.0–9.5 and the Pratylenchus spp. in the range 6.5–9.5, with maximal incidence of P. neglectus at pH 8.2, P. thornei 8.4 and M. brevidens 8.8. Population densities of P. neglectus and especially non-parasitic nematodes were higher in the 0–15cm soil layer than 15–30 cm. Overall the soil conditions of the northern grain region appear more favourable for P. thornei and M. brevidens than for P. neglectus.

Genetic gain in yield and protein over two cycles of a wheat recurrent selection program

Increasing grain yield and protein are important wheat breeding goals. However, the simultaneous improvement of both traits is complicated by a strong negative correlation and genotype by environment interaction (G×E). A recurrent selection program (RSP) reported here was initiated to produce germplasm, which combined both high yield-potential and increased protein content for the northern wheat-growing region of Australia. Diallel crossing amongst 10 cultivars (6 high yield and 4 high quality cultivars), followed by random mating amongst the F1s were used to produce the founding segregating population. Two years of multi-environment trials were conducted in the GRDC Northern Grain Region (NR) for each of the foundation (RSA0) and first (RSA1) cycles of recurrent selection. Data from the two cycles were analysed to evaluate the genetic gain achieved over the two cycles of selection, based on five potential selection strategies. Selection based on yield or protein or yield-adjusted protein only increased selected trait but reduced the other traits. However, application of selection based on yield and protein or yield and yield-adjusted protein simultaneously increased both yield (4.7%, 6.0% for RSA0 and 4.0%, 4.2% for RSA1 respectively) and protein (2.1%, 1.3% for RSA0 and 1.7%, 1.6% for RSA1 respectively).

Diagnosis, extent, impacts, and management of subsoil constraints in the northern grains cropping region of Australia

Productivity of grain crops grown under dryland conditions in north-eastern Australia depends on efficient use of rainfall and available soil moisture accumulated in the period preceding sowing. However, adverse subsoil conditions including high salinity, sodicity, nutrient imbalances, acidity, alkalinity, and high concentrations of chloride (Cl) and sodium (Na) in many soils of the region restrict ability of crop roots to access this stored water and nutrients. Planning for sustainable cropping systems requires identification of the most limiting constraint and understanding its interaction with other biophysical factors. We found that the primary effect of complex and variable combinations of subsoil constraints was to increase the crop lower limit (CLL), thereby reducing plant available water. Among chemical subsoil constraints, subsoil Cl concentration was a more effective indicator of reduced water extraction and reduced grain yields than either salinity or sodicity (ESP). Yield penalty due to high subsoil Cl was seasonally variable, with more in-crop rainfall (ICR) resulting in less negative impact. A conceptual model to determine realistic yield potential in the presence of subsoil Cl was developed from a significant positive linear relationship between CLL and subsoil Cl: Since grid sampling of soil to identify distribution of subsoil Cl, both spatially across landscape and within soil profile, is time-consuming and expensive, we found that electromagnetic induction, coupled with yield mapping and remote sensing of vegetation offers potential to rapidly identify possible subsoil Cl at paddock or farm scale. Plant species and cultivars were evaluated for their adaptations to subsoil Cl. Among winter crops, barley and triticale, followed by bread wheat, were more tolerant of high subsoil Cl concentrations than durum wheat. Chickpea and field pea showed a large decrease in yield with increasing subsoil Cl concentrations and were most sensitive of the crops tested. Cultivars of different winter crops showed minor differences in sensitivity to increasing subsoil Cl concentrations. Water extraction potential of oilseed crops was less affected than cereals with increasing levels of subsoil Cl concentrations. Among summer crops, water extraction potential of millet, mungbean, and sesame appears to be more sensitive to subsoil Cl than that of sorghum and maize; however, the differences were significant only to 0.7 m. Among pasture legumes, lucerne was more tolerant to high subsoil Cl concentrations than the others studied. Surface applied gypsum significantly improved wheat grain yield on soils with ESP &gt;6 in surface soil (0–0.10 m). Subsurface applied gypsum at 0.20–0.30 m depth did not affect grain yield in the first year of application; however, there was a significant increase in grain yield in following years. Better subsoil P and Zn partially alleviated negative impact of high subsoil Cl. Potential savings from improved N fertilisation decisions for paddocks with high subsoil Cl are estimated at ~$AU10 million per annum.