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Abiotic Degradation of the Toxin Simplexin by Soil Collected from a Pimelea-Infested Paddock
No full textPimelea poisoning of cattle is caused by the toxin simplexin present in native Pimelea plant species. Surface weathering and burial of Pimelea plant material under soil in Pimelea-infested pastures previously showed simplexin degradation, suggesting soil microbial metabolism and/or abiotic degradation of simplexin in the field. This current study investigated whether soil from a Pimelea-infested paddock was capable of simplexin degradation in the laboratory. The effects of temperature on isolated simplexin levels and simplexin levels in Pimelea plant material treated with field-collected soil, acid-washed sand or bentonite were determined. Pimelea plant material incubated in field-collected soil at 22 °C for seven days did not show any simplexin degradation. Isolated simplexin preadsorbed to field-collected soil, acid-washed sand or bentonite showed simplexin decrease after one hour of incubation at 100 °C with three breakdown products identified by UPLC-MS/MS, indicating that toxin breakdown can be a heat-induced process rather than a microbial-based metabolism. Decreased simplexin levels were observed in Pimelea plant material mixed with acid-washed sand under similar incubation conditions. Overall, the study showed the field-collected soil did not contain soil microorganisms capable of simplexin metabolism within a short period of time. However, the co-exposure to high temperature resulted in significant abiotic simplexin breakdown, without microorganism involvement, with the product structures suggesting that the degradation was a heat promoted acid hydrolysis/elimination process. Overall, this study demonstrated that simplexin breakdown in the field could be a thermal abiotic process with no indication of microbial involvement
Stakeholders' perspective of the economic cost of managing the invasive Navua sedge in tropical Queensland, Australia
No full textWeeds incur up to AUD 72.91/hectare (AU $82.06 present value). This cost nor the type of management tactics (chemical vs. integrated weed management [IWM]) did not vary between land use types; however, the labor (relative to chemical and machinery) component of the control cost was the greatest. The currently approved herbicide, halosulfuron-methyl (SempraTM), is largely ineffective in controlling the weed due to its inability to deplete below-ground tubers of the weed. Correlation analyses suggest control costs will continue to increase with increasing Navua sedge infestation over time, especially in grazing lands. Farmers show high awareness of the challenge of managing the new weed incursion. Farmers are using myriads of strategies, including willingness to impose strict biosecurity measures and IWM tactics while waiting for more effective herbicides and promising biocontrol agents to minimize the spread and impact of the weed
RNAi Biopesticides for Root-Feeding Insects
No full textRoot-feeding insect pests present a significant challenge to global agriculture, often remaining hidden beneath the soil and causing damage to crop roots before visible signs of damage emerge. Conventional pest control methods, primarily relying on chemical pesticides, have limitations such as non-target toxicity and the development of resistance, necessitating the exploration of alternative approaches. In this context, RNA interference (RNAi) emerges as a natural defense mechanism with potential for the management of various pests, including root-feeding insects. RNAi biopesticides can selectively target-specific genes of root-feeders, hindering their growth, development, and survival, while providing safe and environmental-friendly alternatives adaptable to various delivery methods. This chapter presents a comprehensive review of RNAi studies focused on root-feeding insects for the first time, highlighting the efficacy of RNAi and its impact on different insects. By comparing the effectiveness of representative genes silenced through RNAi and their effects on the growth, development, and survival of root-feeding insects, this chapter enhances the understanding of RNAi as a feasible pest control strategy. Importantly, we explore current and potential RNAi delivery methods, whether through plants, microbes, or the soil, emphasizing the need to address key research gaps, especially the unique challenges for efficient delivery of the RNAi agents to the roots to control the root-feeding insects. Furthermore, we discuss the advantages and disadvantages of different delivery approaches, the possible environmental impact in the long-term, providing insights for future research and the development of RNAi biopesticides for root-feeding pest insects for field application
Development and validation of X-ComEC qPCR, a novel assay for accurate universal detection of both Xylella fastidiosa and Xylella taiwanensis
No full textXylella fastidiosa is a devastating plant pathogenic bacteria known for its broad host range, in contrast to the related species Xylella taiwanensis, which is only known to cause disease in Asian pears. Despite the potential threats they pose to Australian agriculture, diagnostic assays capable of detecting both Xylella species are scarce. Bridging this critical gap, this study presents the development of the X-ComEC qPCR assay that targets a genus-specific DNA sequence, enabling accurate generic detection of all Xylella species. Benchmarking this novel qPCR assay against other published Xylella qPCR assays demonstrated its superior performance. The X-ComEC qPCR assay stands out as the only assay that can accurately detect both X. fastidiosa and X. taiwanensis without cross-reactivity with related bacteria. We have also carried out a comprehensive inter-laboratory test performance study, which demonstrated that the X-ComEC qPCR and the qPCR described by Harper et al. (Development of LAMP and real-time PCR methods for the rapid detection of Xylella fastidiosa for quarantine and field applications; erratum 2013) are highly robust and ready to use in Australia. Combining these two assays into a duplex qPCR enables simultaneous detection and species-level identification of X. fastidiosa and X. taiwanensis. The findings of this study have been incorporated into the Australian National Diagnostic Protocol for Xylella detection, arming diagnostic laboratories with critical knowledge to combat these globally significant pathogens. Overall, the collaborative and systematic approach employed in this study provides a model for developing and validating assays for all plant pathogens
Detection of Invasive Species (Siam Weed) Using Drone-Based Imaging and YOLO Deep Learning Model
No full textThis study explores the efficacy of drone-acquired RGB images and the YOLO model in detecting the invasive species Siam weed (Chromolaena odorata) in natural environments. Siam weed is a perennial scrambling shrub from tropical and sub-tropical America that is invasive outside its native range, causing substantial environmental and economic impacts across Asia, Africa, and Oceania. First detected in Australia in northern Queensland in 1994 and later in the Northern Territory in 2019, there is an urgent need to determine the extent of its incursion across vast, rugged areas of both jurisdictions and a need for distribution mapping at a catchment scale. This study tests drone-based RGB imaging to train a deep learning model that contributes to the goal of surveying non-native vegetation at a catchment scale. We specifically examined the effects of input training images, solar illumination, and model complexity on the model’s detection performance and investigated the sources of false positives. Drone-based RGB images were acquired from four sites in the Townsville region of Queensland to train and test a deep learning model (YOLOv5). Validation was performed through expert visual interpretation of the detection results in image tiles. The YOLOv5 model demonstrated over 0.85 in its F1-Score, which improved to over 0.95 with improved exposure to the images. A reliable detection model was found to be sufficiently trained with approximately 1000 image tiles, with additional images offering marginal improvement. Increased model complexity did not notably enhance model performance, indicating that a smaller model was adequate. False positives often originated from foliage and bark under high solar illumination, and low exposure images reduced these errors considerably. The study demonstrates the feasibility of using YOLO models to detect invasive species in natural landscapes, providing a safe alternative to the current method involving human spotters in helicopters. Future research will focus on developing tools to merge duplicates, gather georeference data, and report detections from large image datasets more efficiently, providing valuable insights for practical applications in environmental management at the catchment scale
Development of multiplex Luminex assays for the surveillance of antimicrobial resistance genes in nasal samples
No full textBovine respiratory disease (BRD) is the major cause of morbidity and mortality in feedlot cattle. It is the major driver for the therapeutic use of antimicrobials in feedlot cattle with their continued use and effectiveness being underpinned through the implementation of stewardship programs that include monitoring of resistance levels. To enable these programs, rapid and user-friendly assays are needed to detect antimicrobial resistance genes (ARG) for efficient monitoring. This study developed multiplex Luminex assays targeting 34 ARGs and validated them using reference strains of Pasteurellaceae and other bacteria, as well as field samples from nasal swabs of cattle (n = 94) undergoing BRD treatment at an Australian feedlot. One swab was collected from each nostril of every animal, with one being used for bacterial culture and conventional PCR analyses for ARGs, while the DNA extracted from the second swab was analyzed using the novel Luminex assays for the presence or absence of the ARGs of interest. The pathogens isolated by culture were tested for macrolide resistance genes erm (Timsit et al., 2017 (42)), mph(E) and msr(E); sulfonamide resistance genes, sul1 and sul2; florfenicol resistance gene floR; β-lactam resistance gene blaRob-1 and tetracycline resistance genes tet(Q) and tet(Y), by conventional PCR. Kappa statistics suggested a moderate agreement between the tests in detecting the macrolide resistance genes. Luminex based analyses identified more resistance genes than PCR on cultured organisms, revealing the presence of a broader array of these genes than previously reported. In addition to detecting more genes, Luminex assays could process a higher number of samples in a single day, making them well-suited for ongoing surveillance of antimicrobial resistance in BRD affected cattle. This capability is essential for optimising therapeutic use and detecting emerging resistance patterns
Diverse human dimensions affect the management of public and animal health impacts of free-roaming dogs in Australia: A One Health solution
No full textThe socio-ecological roles and status of free-roaming dogs (Canis familiaris) in Australian urban, peri-urban and other environments are complex. We review and synthesise those complexities and identify knowledge deficits and impediments to adoption of best practice management of free-roaming dogs. Briefly, perceptions of the roles and impacts of free-roaming dogs in Australia are affected by their status as native, introduced and culturally significant animals, the situations in which they occur and the other species, including humans, with which they interact. Their negative, neutral and positive impacts often occur contemporaneously making free-roaming dogs a 'wicked' problem. We propose and evaluate a One Health-based solution using an environmental psychology perspective in a strategic adaptive management framework. This includes: a typology of free-roaming dogs that assists in the situational definition of animal and public health and welfare issues; identification of some human dimensions affecting management of free-roaming dogs; identification of discipline specialities that require inclusion in an effective One Health approach; audience segmentation, and; priorities for research and policy development to encourage adoption of best-practice management for each occurrence of free-roaming dog impacts
Acclimation of mango ( Mangifera indica cv. Calypso) to canopy light gradients - scaling from leaf to canopy
No full textMango (Mangifera indica), a leading tropical fruit crop, is a prime candidate for intensification through modern orchard-management techniques, including canopy manipulation to improve light interception. This study investigated how leaf-level acclimation to light gradients within the canopy of a high-yield, dwarfing mango cultivar (Calypso™) could be used to examine integrated canopy-scale responses. We quantified foliar morphological, biochemical, and physiological traits across a range of canopy positions using this information to model canopy-scale productivity within digital-twin representations of mango under both conventional (i.e. open-vase) and espalier training canopy systems. Key findings demonstrated that leaves exposed to higher light exhibited increased leaf mass per unit area (LMA), nitrogen content, and photosynthetic capacity (Asat), but decreased chlorophyll-to-nitrogen ratios and photochemical reflectance indices, reflecting trade-offs between light capture and photoprotection. Phenolic content increased under high irradiance, indicating investment in photoprotective compounds at the expense of net carbon gain. Modelled leaf-level productivity increased with light availability, following a Michaelis-Menten saturating response, with diminishing returns under high light. Digital modelling of canopy light interception revealed that espalier-trellis training enhanced light distribution efficiency per unit leaf area but resulted in a 6.5% reduction in total canopy productivity due to a smaller total canopy leaf area. However, when normalized by total canopy leaf area, the espalier-trellis system showed a 3.6% productivity advantage over conventional canopies at the time of year modelled. These results highlight the role of canopy structure and light-use efficiency play in determining orchard productivity. Integrating spatially explicit mechanistic models with LiDAR-derived canopy data offers a promising pathway for designing high-density, resource-efficient mango orchards. Future work should expand modelling to account for dynamic canopy shape throughout the growing season and evaluate the interaction of modified canopy structures with environmental stressors, particularly under climate variability
Characterizing the structural variations in the genome of the mandarin variety, IrM2, induced by gamma irradiation
No full textFruits with few or no seeds are favoured by consumers because they provide an improved eating experience alongside other important quality traits such as taste and shelf-life. Gamma irradiation has been widely used to induce favourable trait changes in plants, including a reduction in seediness. For this reason, it has been extremely important in the development of new commercial citrus cultivars. The variety IrM2 is a mutant derived from the mandarin variety, Murcott, by gamma irradiation. IrM2 has improved consumer and economic appeal due to its earlier fruit maturity time, low number of seeds and improved external skin colour compared with its progenitor. Here, we developed high-quality, haplotype-resolved genomes for Murcott and IrM2, using PacBio HiFi and Hi-C sequencing. The assemblies ranged from 329 to 344 Mb, with N50s of more than 30 Mb, and more than 98% assembly and annotation completeness for the four haplotypes. Duplications, inversions, translocations and INDELs were the predominant types of mutations found in IrM2. Two large heterozygous inversions (3.1 Mb in Chr3 and 8.6 Mb in Chr6) and one large heterozygous, non-reciprocal translocation (between Chr3 and Chr6) were prominent in IrM2 and may be the causes of the reduced seeds. Variations such as insertions and deletions were also found, resulting in additions and loss of genes in IrM2. The genes lost in IrM2 were associated with many processes, including hormone signalling, flowering, DNA transcription, reproduction, gene expression and transmembrane transport. These high-quality genomes contribute to a deeper understanding of how irradiation affects plant genomes
Efficacy of phosphine (PH 3) under hypoxia: pilot and industry‐scale trials for controlling strongly resistant stored product pests in rice
No full textBackground: Phosphine (PH 3 ) is a slow‐acting fumigant, therefore control of resistant insect pests requires high concentrations of 540–1080 ppm (0.75–1.5 g m −3 ) over long exposure periods of up to 21 days. This is difficult to achieve under many practical storage conditions; hence, there is a need to enhance the toxicity of PH 3 , so that resistant insects can be eradicated in a shorter fumigation time. Co‐fumigation with PH 3 , along with other atmospheric gases (carbon dioxide (CO 2 ) and nitrogen (N 2 )), enhances PH 3 toxicity in laboratory‐scale experiments; however, this information has not been translated into practical pest management protocols for adoption by the industry.
Methodology: The effectiveness of co‐fumigation with PH 3 plus two of the atmospheric gases (N 2 and CO 2 ) was evaluated in fumigation chambers and commercial‐scale rice storage silos. Strongly PH 3 ‐resistant insects of mixed life stages of key grain insect pests, Rhyzopertha dominica, Tribolium castaneum, Sitophilus oryzae, and Cryptolestes ferrugineus were placed in cages inside the mini‐fumigation chambers or silos containing freshly milled rice grains. Fumigations were performed with currently registered application rates of PH 3 (0.75–1.5 g m−3) in combination with selected concentrations of CO 2 (5–30%) and N 2 (90–98%)/low oxygen (O2, 5–10%) over a short exposure period of 4 days. Test insect cages were retrieved after venting, and the effectiveness of the hypoxic fumigation was evaluated in terms of per cent mortalities of adults and progeny.
Results and conclusion: Both the pilot scale and field fumigation research confirmed that the triplet mixture, PH 3 0.75–1.0 g m −3 + high N 2 (90–95%) + CO 2 (5–20%) over 4 days was very effective against three strongly PH 3 ‐resistant species, R. dominica, T. castaneum, and S. oryzae and caused complete adult and progeny mortality. However, higher concentrations of this triplet mixture, PH 3 1.5 g m −3 + high N 2 (90–95%) + CO 2 (30%) over 4 days was required to achieve complete mortality of adults and progeny of strongly resistant C. ferrugineus. At both the low and high co‐fumigation dose rates, the required minimum effective PH 3 concentrations (540–1080 ppm) were maintained over the 4‐day exposure period, confirming the reliability of these rates for industrial applications