The low responsiveness of cotton (Gossypium hirsutum L.) to phosphorus (P) fertilizers in the field where soils have low soil test values for P, suggests that cotton is capable of utilizing soil P pools that are less labile or are below the depth of P fertilizer placement. The objective of this thesis is to understand how the cotton plant acquires P from less labile and subsoil P pools.

The first experiment was conducted using rhizoboxes to examine whether cotton is physiologically efficient at acquiring less labile P pools, through comparison with wheat (Triticum aestivum L.) and white lupin (Lupinus albus L.). Under P-deficient conditions, cotton released negligible carboxylates into the rhizosphere. The P depletion zone of cotton from rhizosphere soil was less than 2 mm, and predominantly from the relatively labile NaHCO3-Pi and NaOH-Po pools. In contrast wheat and white lupin markedly depleted the NaHCO3-Pi and less labile HCl-P pools, and the depletion zone extended to 3 mm. The depletion of NaOH-Po pools by cotton was associated with increased activity of phosphatises in the rhizosphere soil.

A second sand culture experiment investigated the ability of cotton to access P from the sparingly soluble P sources of AlPO4, FePO4 and hydroxyapatite. The experiment revealed that cotton was inefficient in accessing P from all these sparingly soluble P sources. In contrast, wheat showed an outstanding ability to use AlPO4. The 32P reverse dilution technique was then used to determine the variation between these species in accessing sparingly soluble AlPO4 and hydroxyapatite in a Vertosol when N was supplied as different forms. The inefficiency of cotton to access P from these sources was again documented. The percentage of hydroxyapatite recovered by the cotton plant was 8 and 10 times lower than that recovered by wheat and white lupin respectively, while the availability of AlPO4 to cotton was 10 times lower than wheat but 3 times higher than white lupin. Addition of N as NH4-N elevated total plant P uptake from all P sources except in the case of wheat fed with Al-P. The fate of these P sources in the soil was examined in a separate incubation experiment Sparingly soluble Al-P was more ‘labile’ in Vertosols, in comparison to FePO4 and hydroxyapatite which showed little change in availability with time.Hydraulic lift can be a desirable characteristic for P acquisition by crops growing in areas that experience frequent drying of the topsoil. A glasshouse experiment using specialized soil columns tested whether cotton could hydraulically lift water and whether this hydraulically-lifted water facilitates P acquisition from dry topsoil. Hydraulic lift was detected in a Vertosol for 7 days after water was withheld from the topsoil. However, the hydraulic lift detected for the cotton did not aid P acquisition from the dry topsoil. Therefore, it appears that if the topsoil dries out, P uptake by the cotton plant would rely mainly on P acquisition from P sources in the subsoil.

The contribution of subsoil P sources to plant uptake was investigated in two field surveys. Soil samples at various soil depths were collected from continuously-cultivated cereal and cotton paddocks, and corresponding virgin sites, in north-western NSW. Regardless of P fertilizer history, organic and residual P pools at depths of 0 to 45 cm had been invariably depleted following long-term continuous cotton and cereal cropping. With a negative Pbalance, the HCl-P pool below 10 cm also declined significantly. Thus, routine soil P tests, using alkaline bicarbonate extraction solutions with soil samples collected from the topsoil layers (above 10 cm), were less accurate in estimating P responsiveness of cotton to P fertilizers applied on Vertosols. The effect of cropping system, expected from species ariation in root morphological and physiological characteristics, on the soil P accumulation and depletion profile was undetectable.

The results suggest that the low responsiveness of cotton to P fertilizers can be attributed to a number of causes. These include the utilization of organic P pools, subsoil P exploration or possibly mycorrhizal symbioses, rather than any efficient P acquisition from sparingly soluble inorganic P pools in the topsoil. Further research should focus on accurately estimating the contribution of organic P and subsoil P pools to P uptake by cotton plants.

The objective of this project funding was to maximise profitability by improving the efficiency and flexibility of broadacre irrigation systems. This was identified as a priority for research by grower groups based in the southern connected systems of the Murray Darling Basin. To achieve the objective, the project had four focus areas:

* to foster collaboration and partnerships to facilitate the adoption of research findings

* to investigate irrigation and nitrogen management strategies to improve water productivity in cotton, maize and rice farming systems

* to develop best practice design guidelines for basin surface irrigation systems

* to investigate the economic impact of investment in irrigation development on whole-farm profitability.

The key messages:

* This project enabled collaboration across two research organisations, four advisory organisations and three grower groups to investigate improvements in water productivity in a region in which approximately 4000 gigalitres (GL) is used by irrigated agriculture.

* Complex relationships exist between irrigation, nitrogen and plant development that require appropriate management to avoid negative impacts on profitability.

* Improvements in on-farm irrigation infrastructure can achieve a significant marginal rate of return on the capital investment, with potential for further improvement subject to better irrigation layout design and drainage.

Alternative and renewable energy sources, including solar for powering cotton production, were hot topics at the February 2015 CottonInfo Big Day Out at St George, QLD. One of two Big Day Outs, the Gunnedah event was hosted by cotton grower Scott Morgan, with support from CottonInfo, its partners CRDC, Cotton Australia and CSD, and the Commonwealth Department of Industry and Science. This video provides a snapshot of the event and its key highlights.

A two year project that investigated the influences of weathering, insect honeydew and fungal agents on cotton colour grades, yarn and fabric quality parameters provided a better understanding of these factors and the conditions under which they occur. Extended weathering in the field, particularly with successive rainfall events totalling 100 mm, was detrimental to cotton colour, reducing colour from base grade to 41 and beyond. In both years of the project this equated to 10 weeks in the field from the time of first open boll. Moist, overcast conditions for 4 -7 days were usually followed by a drop in colour grade. Short, sporadic rainfall events followed by sunshine did not cause colour degradation. The humidity they provided could, however, further the development of sooty mould fungi which grew on honeydew contaminated cotton. While sooty mould fungi can grow on the natural sugars of immature fibres in the absence of moisture, both the presence of insect honeydew and rainfall strongly promoted their development, reducing cotton colour from base grade to 41 to 71. The magnitude of the colour drop depended on the amount of black spores on the boll surface. Increasing development of sooty mould fungi was also correlated with a reduction in sugar concentration on bolls, providing some evidence of the ability of fungi to remove sugar from honeydew contaminated cotton. Sooty mould spores in cotton fields are rarely just blown out during harvesting. It was found that spores strongly adhere to open bolls and survive through the harvesting process to worsen the colour grade of the harvested lint. However, one or twocolour grades may be restored through the ginning process. Between 30-50% of heavily contaminated sooty mould cotton in the total pick can drop colour grade from base grade to incur penalties. Colour grade, while not showing effects on lint or yarn quality in these experiments, was strongly related to dyeability of fabrics. Cotton colour degraded through weathering and rainfall affected dyeability more that colour degraded through sooty mould fungi and this was most likely associated with the lower moisture levels received by the sooty mould cotton. SEM scans did not show obvious surface changes due to sooty mould activity.

At this stage options for mitigation of the degradation of colour grade are not available. There is no mitigation for rainfall and growers already aim to harvest their crop as timely as possible to avoid weathering and colour degradation. Agronomic and management practices are being investigated in a continuing project. As colour degradation due to sooty mould development largely depends on the presence of sugars in the form of insect honeydew, the most important goal a grower should have is to avoid insect pests such as whiteflies, aphids and mealybugs. This can be achieved through sound, IPM guided crop management using IPM compatible insecticides to control early season pests such as mirids in order to preserve beneficials that later on help with management of Silver leaf whitefly (SLW). Should conditions conspire, and a crop is sticky without rainfall in sight, a range of scenarios may be managed with suitable knockdown insecticides which may reduce SLW numbers until defoliation is complete. On the other hand, if rainfall is in sight, sticky cotton can benefit from this but incurs the risk of sooty mould development. Fungicides tested in this project have the potential to prevent sooty mould development, however, none are currently registered for use on cotton (other than as seed treatment). If registration becomes an option in the future, many parameters would have to be considered including environmental impact, pre-harvest withholding periods, inherent effects on lint, application efficiency and cost. Further research into mitigation options are being addressed in CSP 1901“Reducing the impact of weather, insects and microbes on cotton colour”, a collaboration between Dr Simone Heimoana (Simone.Heimoana@csiro.au) and Dr Stuart Gordon (Stuart.Gordon@csiro.au). Management of honeydew related cotton discolouration is up to the individual grower and while sooty mould tends to affect the individual grower with colour discounts, sticky cotton has the potential to penalise the entire industry.

Declining water quality and quantity is a threat to the production of food and fibre worldwide. While irrigation using marginal quality saline-sodic (MQSS) water is emerging as a more common practice, it is still an under-utilised resource because of its potential detrimental impact on soil structure and crop production. The aim of the research was to enhance the current understanding of, and capability to, strategically utilise saline-sodic water as an irrigation resource through further investigation of the theory of threshold electrolyte concentration (C TH).

I attended the 3rd Agriculture and Climate Change conference held in Budapest, Hungary from the 24th-26th March 2019. The focus of the conference was on the various challenges of climate change, reduced water availability and approaches to the production of climate resilient crops, which is highly relevant to my current CRDC-supported research CSP 1804: Water use efficiency in a changing climate. Attending this conference provided me an opportunity to present CRDC-supported research on the integrated effects of warmer temperatures and elevated CO2 on leaf physiology, growth, water use and water use efficiency to the international scientific community. It also provided me an opportunity to engage and network with international scientists researching effects of climate change on a wide range of agricultural systems.

This study examines the effectiveness of publicly-available data to identify farm-scale regions of similarity, and classifies the distribution of physical (available water capacity (AWC)) and chemical (pH and electrical conductivity (ECe)) soil constraints in a northern NSW dryland cotton system. The incorporated open-source information could identify spatial variability in key soil attributes, though further data accuracy improvements will be increasingly valuable. ECe (salinity) levels were low, and there was no relationship between AWC and cotton or wheat yield. However, a strongly alkaline pH within a crops capable rooting depth across 70% of the property was identified, with an easily interpretable depth to pH constraint map produced. While depth to pH constraint had a major impact on wheat yield, no impact on cotton yield was observed. Such a discrepancy highlights the importance of analysing multiple years of crop yield monitor data as the most limiting soil constraint may vary based on seasonal conditions. The accurate characterisation of depth to pH constraint across both the property and region will assist in classifying its influence on other crop types and growing seasons in an overall bid to overcome its possible negative implications on productivity and profitability via the adoption of best management practices. Further work will focus on using the developed approach to map the depth to other important soil constraints, such as sodicity.

The Nucleopolyhedroviruses (NPV) are dsDNA invertebrate-specific obligate pathogens of the insect orders Lepidoptera, Hymenopteran and Dipteran belonging to the family Baculoviridae (Baculovirus). An NPV consists of a genome with lengths between 80 and 180 kbp and a community of phenotypically and genetically diverse virus strains that are co-occluded within a protein body. NPVs are widely used in biological control of Lepidopteran pests, and understanding isolate dynamics, diversity and evolution is important in resistance management strategies and developing next generation biopesticides with desired phenotypic traits.

The aim of this study was to apply next generation sequencing and develop bioinformatic techniques to expand and accelerate current knowledge of baculoviruses by studying the dynamics, diversity and evolution. This included the development of a new bioinformatic pipeline to analyse the within-isolate and within-strain diversity, applying this pipeline to monitor the change in genotype abundance during the infection cycle and derivatisation of in vitro and in vivo selected strains from a wild type isolate of commercial importance, Helicoverpa armigera Single Nucleopolyhedrovirus (HaSNPV) isolate AC53 (AC53). Derived genomes were analysed to identify trait or isolation technique specific mutations, and the global relationships of these strains to all known HaSNPV isolates.

Phylogenetic analysis of all known HaSNPV and H. zea SNPV isolates with the addition of AC53 and some of its derivatives supported the claim that these viruses are the same viral species, and suggests that the HaSNPV species may have originated in Australia. The use of whole genomes in phylogenetic analysis gave greater resolution than the more commonly used analysis using selected open reading frames.

Five strain derivatisation approaches were applied: two in vitro (in tissue culture) and three in vivo. Analysis of both in vitro and in vivo -derived strains genomes identified selection specific mutations, with fast speed of kill, slow speed of kill and maximum virus production strains containing trait specific mutations. Biological characterisation of these trait-specific strains identified significant virulence-transmission trade-offs such as enhanced speed of kill but reduced efficacy which implicates commercial optimisation of strains.

A new software pipeline called the ‘Meta-barcoding Genotyping and Abundance Pipeline’ (MetaGaAP) was developed to identify genotypes and their relative abundance within the AC53 isolate. This was validated by Sanger sequencing and comparison to the AC53-T2 strain. The pipeline was applied to monitor AC53 during the infection cycle and identified two evolutionary effects occurring within the population; weak-negative selection with mutation bias and a ‘drift barrier’ to limit the effects of genetic drift. Furthermore, time-course assays revealed a significant reduction in dominant genotype abundance with an increase in minor genotype abundance when the initial viral stock is compared to the final viral product. This implicates commercial production as the starting material and the produced material contain different genotype abundance profiles, however, both products contain the same genotype composition.

In addition, results presented throughout this study suggested that NPVs fit the viral quasispecies model as mutations that arose were the result of mutational robustness and genotype cooperation. Limitations observed with current NGS and bioinformatic techniques partially impacted the described results but may eventually resolve with advent of third-generation sequencing

In 2017-18, CRDC invested $25.1 million into 318 RD&E projects in collaboration with 118 research partners and growers who conducted on-farm trials, across five key program areas: farmers, industry, customers, people and performance.

CRDC’s role is to invest in RD&E on behalf of cotton growers and the government, with the outcomes boosting the productivity and profitability of our industry. RD&E, and its resulting innovations, are a key driving force behind the Australian cotton industry’s continued success.

The findings from these research projects continue to be extended through a range of methods, including the industry’s joint extension program CottonInfo. The adoption of best management practices is also encouraged via the industry program myBMP. CRDC is a founding partner of both programs.

The Green Vegetable Bug, Nezara viridula, has recently become a more significant pest of Australian cotton but it is not a problem every season. This project addressed aspects of the multiple host use and movement of N. viridula as they relate to cotton, as well as the genetic relationship between Australian N. viridula and the global populations of this pest.

Samples of N. viridula were collected from northern and eastern Australia and from a variety of weed and crop hosts, with an emphasis on cotton. The abundance of N. viridula was low for the duration of the project but about 800 adult insects were collected overall. Comprehensive phylogenetic and population genetics methods were used to address each of the questions. The methods developed during this study will be made available to other researchers through scientific publications.

The Australia populations of N. viridula come from two different evolutionary lineages, one European and one Asian. The former is distributed across eastern Australia and the other across northern Australia. At some point in the past some individuals of the Asian lineage have mated with individuals of the European lineage in northern Queensland but these events appear to have occurred only rarely. Across the different host plant species there are no genetic differences between N. viridula that would indicate separate host-specific gene pools.

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The N. viridula in eastern Australia are more genetically distinct from one another the greater the geographic distance that separates the sampling localities from which they were collected. This slight genetic differentiation over geographic distance is present in insects collected across two years and this indicates that N. viridula populations remain relatively localised in the short term. This result indicates that the host plants available to N. viridula within each cotton growing region will be the most relevant for predicting the abundance of this insect in cotton. Pest pressure from N. viridula was low for the duration of the project and so this pattern may be different during seasons when N. viridula is present in high numbers. In years of high abundance host plants might be found between growing regions, and allow for the recruitment of N. viridula over a wider area.

Future research that addresses the host use of N. viridula should investigate populations from each cotton growing region independently, as local conditions, such as the crop and weed host plants used by N. viridula each season before cotton becomes attractive, will be the most relevant to late season numbers of this insect in cotton. A previous CRDC funded project has already addressed N. viridula host use in central New South Wales. If cotton is grown regularly in northern Australia then it would be prudent to treat the N. viridula population there as a separate entity, as there may be significant differences in their biology which could affect their host use and abundance in cotton. Any differences would therefore influence the development of management strategies.