Insects can respond to selection pressure by mobilising new defence mechanisms. In contrast to recessive resistance mechanisms based on rare target site mutations in receptor proteins, leading to extreme resistance to high B. thuringiensis (Bt) toxin concentrations, we observed a “hidden” inducible immune and metabolic tolerance in field derived laboratory populations of H. armigera to Cry1Ac and Cry2Ab toxins, with potential to cause ecological and economic problems in cotton production. Given that offspring from insects surviving in the field are tolerant of Bt but do not exhibit resistance to Cry1Ac and Cry2Ab due to target site mutations, it is likely that other mechanism(s) is assisting larvae to survive on certain parts of the plants or late in the season when toxin expression is low. Importantly for cotton bollworm management, we have the following three main outcomes:

1) Tolerance in H. armigera larvae is induced by gut-derived toxins (both Cry1Ac and Cry2Ab) and creates sub-populations of insects that show significant levels of tolerance without displaying mutational changes in a major resistance gene locus. Instead, the tolerant phenotype is caused by differential regulation of immune and metabolic activities (larval induction), and is transmitted to offspring by an epigenetic mechanism showing a maternal effect (embryonic induction). While the epigenetic contribution to incremental increases in tolerance is prominent under low to medium selection pressure, other resistance mechanisms that are transmitted genetically may predominate over time with incremental increase in toxin exposure.

2) Testing gene expression in tolerant and susceptible neonate larvae indicates that a range of genes are expressed significantly differently (both higher and lower expression) in tolerant insects compared to susceptible control. Although some of these differentially expressed genes are important key receptor, putative immune and catalytic genes, most of the differentially regulated genes (up to 190 fold) are unknown in function. By understanding these highly altered unknown genes, it is likely we will gain an understanding of the tolerance mechanism and able to develop management options to specially counter tolerance buildup. Further, significant differential regulation of key receptor genes opens up avenues for further research that may lead to establish monitoring tool to detect inducible tolerance and/or resistance in the field.

3) There appears to be significant developmental penalties under laboratory selection, as evidenced by lowered larval weights and increased developmental times. However, once the populations were kept at constant toxin levels, the developmental penalties slowly diminished over subsequent generations. This could indicate possible genotype selection of allelic combinations of multi-gene functions that reduce developmental penalties. This may in long term provide tolerant populations with the adaptive potential to acquire resistance mechanisms that are genetically transmitted and involve target site mutations in important resistance genes. Our findings have practical significance for adapting pest management protocols to counter inducible tolerance, particularly the importance of susceptible females in blocking this form of resistance.

Lastly, laboratory selected H. armigera (25 generations selected with Cry1Ac, 63 fold resistance) are able to complete their larval development on transgenic cotton expressing Cry1Ac and produced fertile adults (Akhurst et al., 2003). Therefore, whether incremental increases in tolerance can support selection for target site mutations in key receptors allowing insect larvae to survive on Bt-plants is another key issue that requires investigation.

Knowledge is fundamental to improving the competitiveness, responsiveness

and levels of innovation that we see in industries. This research project completed interviews with

90 growers of cotton and grains, consultants, extension workers, government researcher officers,

and irrigation equipment suppliers to determine how information and knowledge about water

management and water use efficiency is being used and managed in irrigated cotton and grains. Four key issues affecting water management were identified as having major impacts on water management. Information, knowledge and knowledge sharing. All groups believed that the industry was

responsive to change, willing to continually learn, and that growers, consultants and extension

officers were very willing to share information and knowledge. There was considerable

information that was available to growers and consultants. A major concern, however, among

growers and consultants, was the need for the information to have been tested and applied to

determine its relevance and applicability to specific regions.

There is currently a shortage of irrigation water available for cotton production in Australia due to recent climatic and legislative conditions. Some growers have responded to this water shortage by changing from traditional furrow irrigation to alternative irrigation systems such as centre pivots and lateral move irrigations (collectively known as large mobile irrigation machines – LMIMs). Improved efficiency of irrigation application, as well as labour savings, have been the main reasons for the increased adoption of LMIMs. The use of LMIMs also enables a higher level of control in water application in terms of irrigation volume, timing and placement. As a result, growers now have much greater control over soil moisture conditions which enables the implementation of improved irrigation management strategies that have the potential for improved crop water use efficiency (WUE).

Two irrigation strategies which have been demonstrated to achieve benefits in terms of crop WUE are partial rootzone drying (PRD) and deficit irrigation (DI). PRD and DI involve manipulating the placement of irrigation water and the moisture deficit maintained in the root zone, respectively. Neither PRD nor DI is able to be applied easily under furrow irrigation. However, both PRD and DI may be able to be implemented under LMIMs within the cotton industry. Deficit irrigation has been shown to be effective at improving WUE in cotton, although it is not widely used within the Australian cotton industry. Similarly, there has been little research conducted to identify whether cotton responds to partial rootzone drying and there is currently little understanding of the way in which DI and PRD strategies could be implemented commercially using LMIMs.

This research investigated the response of cotton to a range of PRD and deficit irrigation strategies under LMIMs. Assessment of the biochemical and physiological response of cotton to irrigation strategies were conducted under glasshouse conditions. Field trials conducted under a commercial centre pivot and lateral move assessed the crop response, soil moisture movement, yield and WUE associated with the implementation of a range of PRD and deficit treatments. Modelling of rainfall probability and soil moisture movement were also undertaken to quantify constraints to the successful commercial implementation of irrigation management strategies such as PRD within the Australian cotton industry.

Weather and climate news 10 August 2015

Weather and climate news 24 August 2015

Weather and climate news 27 September 2015

Weather and climate news 07 September 2015

The Grassroots Program offers Cotton Grower groups the opportunity to apply for community based assistance.

Weather Station Upgrades: The Darling Downs Cotton Growers Inc (DDCGI), and individual growers established 21 weather stations between the period 1996-1998, to provide growers with localised weather information to assist with on-farm management operations. The DDCGI has maintained these stations over this period, and in recent years, been working on major upgrades to digital technology to enable text communication with growers rather than the old analogue voice system. To date 11 stations have been upgraded by the DDCGI, and funding from this grant contributing to upgrading another four stations.

Chemical Application Workshops: It is vital for growers to maintain a high level of responsible chemical use and efficient crop protection through continued improvement, uptake a new technology and adoption of best practice. Spray drift is not only a risk of susceptible crops, non-target and sensitive areas but also to the future access of certain groups of chemicals. In addition, poor application methods and reduced efficacy contribute to the development of resistance. The DDCGI is committed to responsible chemical use and the stewardship of agricultural chemicals. The DDCGI plans to use funding from this grant towards organising three training and extension days across the region, the focus will be on chemical application best practice, spray drift risk management, understanding the local weather conditions and record keeping compliance. The DDCGI will engage the services of Mary O’Brien Rural Enterprises to deliver these workshops.

The cotton industry spends about $8M on P fertilizers and about $5M of K fertilizers. This indicates the extent of recognised P and K deficiency. It is envisaged that many cotton-growing soils are nearing deficient status, as continual cotton cropping quickly depletes these nutrients. Identification of these soils through soil and plant testing and formulation of improved fertilizer management practices will avoid nutrient deficiencies that reduce the productivity and profitability of cotton cropping.

Inadequate P and K nutrition are responsible for substantial losses of yield and profitability in cotton farming. Deficencies of both nutrients have been linked with the premature senescence syndrome, although confusion arises between the importance and the interactions of these two nutrients.

Previous research has indicated levels of available soil P at which response to P fertilizer is expected and P fertilizer recommendations for maintaining levels of soil P to adequate crop P nutrition. Similarly, research has been conducted on the association between K nutrition and premature. However, the influence of soil sodicity on the P and K nutrition of cotton has now been recognised and a significant effort is required to determine its importance and economic relevance to production.

The cotton simulation model, OZCOT, is an important component of a number of current and future projects. It is a key tool both for exploring cotton crop responses and as a means of extending the outcomes of science into the industry. In this project we aimed to ensure the ongoing maintenance of the model as well as the continued incorporation of new science to improve our capacity to deal with current industry issues.

The project covered three main research components: 1.) exploring varietal differences in determinacy, 2.) exploring the model’s capacity to simulate compensatory growth responses to insect damage, and 3.) implementing a new soil water balance in the model. These areas were identified as being of current high importance by a meeting of researchers associated with the project, including Drs Greg Constable, Lewis Wilson, Mike Bange and Brian Hearn. Ensuring the model’s capability to simulate compensation is important for specific applications but the issues of growth form and soil water extraction are important for the general performance of the model and hence its application to a range of issues.

A complete review and restructure of the model has been undertaken. In addition to meeting existing usage requirements, the restructure has allowed considerable advances to be made towards making the science included in the model readily available to a much wider audience through conforming the model components to CSIRO Plant Industry’s Common Modelling Protocol.

Modifications have been made to the model to allow it to respond to pest damage. Research is underway to refine these modifications with the aim of developing a version of OZCOT that can be linked with EntomoLOGIC to improve pest management decisions and reduce insecticide use.

Coding for the use of the Montieth-Passioura approach in the Ozcot model has been completed is a version of the model using this approach has been developed. Collection of data for validation and for the development of a database of parameters for different soil types has been impared by drought and the reduced plantings of dryland crops.

This is the first study of which we are aware to attempt to derive an objective, quantifiable measure associated with determinacy in cotton. Two indices were developed which were well correlated to the breeders’ field assessment of determinacy, suggesting that they might provide a suitable basis for an index of determinacy. The measure based on rate of decline in nodes above last flower is the simpler of the two for field use.