Risk Assessment Of Exotic Plant Diseases To The Australian Rice Industry, With Emphasis on Rice Blast

A pest risk assessment was carried out using all available information found in the literature and also two softwares developed by the CSIRO, CLIMEX and DYMEX. CLIMEX was used to assess the suitability of the climate in Australian rice growing area for each pest/disease and then when necessary and possible, a pest/disease model was created with DYMEX and run with Australian climatic data. The Australian climatic conditions and/or the rice growing practices were found to be unfavourable for the majority of the exotic diseases. However, two diseases of rice (rice blast and kernel smut) and one plant parasitic nematode genus (root nematodes) were identified as having the potential to threaten the Australian rice industry if ever introduced in south eastern Australia

Exotic fungal spores in the Australian Plant Biosecurity context

This project aims to define the relative likelihood of, and means by which, exotic fungal spore incursions on or in different carrier materials can occur by assessing common pathogen species in Australia and likely entry pathways and develop effective methods of decontamination of such infested materials. In Australia, the risk of inadvertent introduction of exotic fungal pathogen particularly by spores is increasing. Many of these exotic fungal pathogens pose a threat to our agricultural, horticultural and natural ecosystems if introduced into Australia e.g. Ug99. This research will improve the current understanding of the different entry pathways of fungal pathogens to Australia. The research project will specifically focus on the role of different materials as fungal spore carriers and their effects on spore survivability using common fungal spores as a model to develop and apply prototype tools to detect the contamination of carrier materials with exotic fungal pathogen threats, and develop effective methods of decontamination of such contaminated materials

Long-term viability of the northern anthracnose pathogen, Kabatiella caulivora, facilitates its transportation and spread

The conidia and resting hyphae of the northern anthracnose pathogen of Trifolium species, Kabatiella caulivora, were effectively carried by, and maintained long-term viability on, a range of materials, including metals, fabrics, woods and plastics. Conidia and hyphae became thick-walled and melanized with time. There were significant (P < 0.001) differences in conidia/resting hyphae survival between carrier materials and between temperature regimes. At 23 °C/8 °C day/night, conidia and resting hyphae remained viable on steel, corrugated iron, galvanized steel, all tested fabrics, wood and random mixed materials for up to 8 months. At 36 °C/14 °C day/night, conidia and resting hyphae remained viable for up to 8 months, but only on cotton, denim, fleece, silk, leather, paper, plastic and all wood materials. At 45 °C/15 °C day/night, conidia and resting hyphae remained viable up to 8 months only on fleece wool, Eucalyptus marginata (jarrah wood) and paper. There were significant differences between carrier materials in their abilities to retain conidia and resting hyphae after washing (P < 0.001). Metabolic activity was confirmed for conidia and resting hyphae recovered after 8 months and K. caulivora colonies successfully re-established on potato dextrose agar. Findings confirmed the critical importance of materials as long-term carriers of viable K. caulivora conidia and resting hyphae, highlighting the potential for spread of a highly virulent K. caulivora race within and outside Australia via farming equipment, clothing and other associated materials. Results also have wider biosecurity implications for the transportation of fungal-infested carrier materials previously considered as low risk

Extended survival of Puccinia graminis f. sp. tritici urediniospores: implications for biosecurity and on-farm management

Puccinia graminis f. sp. tritici (Pgt), the causal organism of stem rust, is of global importance across wheat-growing countries. However, some epidemics commence without the obvious presence of ‘alternate’ or ‘green bridge’ hosts, suggesting urediniospores can survive in the absence of suitable host plants for many weeks. Testing a range of inert material types, including metals, plastics, fabrics and woods, highlighted a significant effect of material type and temperature on urediniospore viability (P < 0.001), with urediniospores remaining attached and viable on these materials (aluminium, paper, rubber, all fabric and all woods) for up to 365 days at 23/8 °C day/night. At 36/14 °C day/night, urediniospore viability was retained for a maximum of 300 days on denim and jute. Furthermore, at 45/15 °C day/night, urediniospores remained viable for a maximum of 180 days on cotton and jute. The frequency of recovery of attached urediniospores was also dependent upon the material type, with significant differences between materials in their abilities to retain urediniospores after washing (P < 0.001). Urediniospores recovered even after 300 or 365 days from the lower two temperature regimes successfully initiated infections of wheat seedlings. Results confirm the potential importance of inert materials as long-term carriers of viable Pgt urediniospores, highlighting risks of spread of new pathotypes and strains across wheat-growing regions, the significant biosecurity implications for contaminated carrier materials, and its likely survival across seasons without a host

Movement of pathogens between horticultural crops and endemic trees in the Kimberleys

Recently a survey of endophytes associated with boabs (Adansonia gregorrii) and associated tree species in the Kimberleys, Western Australia has resulted in the description of seven new species in the Botryosphaeriaceae (Pavlic et al. 2008). Additionally several common species of Lasiodiplodia, (L. theobromae, L. pseudoptheobromae and L. parva) were also isolated as endophytes of endemic tree species. Concurrently, surveys in the Ord River Irrigation Area (ORIA) have revealed Mangiferum indica trees showing symptoms of dieback and cankers. In this project we isolated, identified and determined the pathogenicity of fungi associated with these cankers

Pathogenic Botryosphaeriaceae associated with Mangifera indica in the Kimberley Region of Western Australia

Members of the Botryosphaeriaceae, in particular Lasiodiplodia theobromae, Neofusicoccum parvum, N. mangiferum and Botryosphaeria dothidea, commonly cause stem cankers, dieback and stem end rot of mangoes worldwide. In the current study, eight taxa of Botryosphaeriaceae were identified as canker-associated fungi, pathogens, potential pathogens or endophytes of mangoes in the Kimberley, Australia. These include Neoscytalidium novaehollandiae, Ne. dimidiatum, Pseudofusicoccum adansoniae, P. ardesiacum, P. kimberleyense, Lasiodiplodia sp. 1, L. iraniensis and L. pseudotheobromae. The pathogenicity of a selection of these species toward fruit and branches was tested. All were pathogenic to mango in comparison to the control, with Lasiodiplodia spp. being the most pathogenic. It appears that either geographic isolation or the unique growing conditions in the Kimberley may have provided an effective barrier to the acquisition or establishment of known botryosphaeriaceous pathogens. Wounds caused by mechanical pruning may provide an entry point for infection, whilst severe pruning may increase plant stress

A rapid and miniaturized system using Alamar blue to assess fungal spore viability: implications for biosecurity

Long-lasting viable fungal spores are one of the important aspects in emergence, spread and disease development of pathogenic fungi. We developed a rapid and miniaturized system using Alamar Blue (resazurin dye; 7-hydroxy-3H-phenoxazin-3-one 10-oxide) for assessing fungal spore viability, using the ascomycete Leptosphaeria maculans (causing blackleg disease on canola) as a ‘model pathogen’. The assay is dependent on the metabolic activity of viable fungal spores to convert the dark blue of resazurin (maximum absorbance 605 nm) into the pink colour of resorufin (maximum absorbance 573 nm). The Alamar Blue assay uses an optimised micro-titre based format that was far superior for determining fungal spore viability in comparison with current conventional techniques including trypan blue staining, a TC10 cellometer cell counter, or by assessing germination of the spores under the microscope. This new assay was also more rapid and reproducible than current conventional tests to detect viable spores. Viable spores could be reliably detected within two hours. The successful application of the Alamar Blue assay to measure fungal spore viability in the current study has important benefits for biosecurity operations relating to faster and more reliable confirmation of viability of potential invasive exotic fungal pathogens and in minimising any consequent disease outbreaks. The effectiveness of the Alamar Blue assay was confirmed by successfully determining the relative retention times of viable L. maculans ascospores across a range of different potential spore-carrier materials, including steel, fabric, wood, paper, rubber and leather, over a time period of eight months. To further confirm the wide applicability of the Alamar Blue assay, it was successfully applied to detect viable spores of fungal pathogens of diverse taxonomic groups, including Kabatiella caulivora, Magnaporthe oryzae and Puccinia striiformis f.sp. tritici, and also of the yeast Saccharomyces cerevisiae

Disinfestation of diverse fungal pathogen spores on inert contaminated materials

In vitro studies were undertaken to determine the effects of five fungicide and disinfectant treatments [propiconazole (Tilt 250EC), azoxystrobin (Amistar 250EC), didecyldimethyl ammonium chloride (Sporekill), alkali metal salts of alkylbenzene sulfonic acid and coconut diethanolamide (Farmcleanse), and potassium peroxymonosulfate (Virkon)] in preventing the germination of spores of Puccinia graminis f. sp. tritici, Kabatiella caulivora, Leptosphaeria maculans and Magnaporthe oryzae. Germination was inhibited by all fungicides and disinfectants, with maximum reductions at the manufacturer’s recommended concentration. Overall, azoxystrobin was the most effective, reducing germination of M. oryzae by 89%, L. maculans by 78% and P. graminis f. sp. tritici by 77%. Propiconazole was the most effective in reducing germination of K. caulivora by 72%. The extent of inhibition of germination was dependent on the pathogen; for example, alkali metal salts of alkylbenzene sulfonic acid and coconut diethanolamide, and potassium peroxymonosulfate were more effective on M. oryzae and P. graminis f. sp. tritici compared with L. maculans or K. caulivora. Studies undertaken to define the effectiveness of the fungicides/disinfectants reducing germination of the pathogens on five inert carrier materials (steel, fabric, wood, paper, and rubber) showed azoxystrobin and propiconazole to be the most effective, having 12–15% spore germination following decontamination treatment of carrier materials. The results demonstrate the potential for increased use of fungicides, particularly demethylation inhibitor and QoI fungicides, to decontaminate carrier materials to address the critical need to implement a practical commercial solution for dealing with threats posed by the long-term viability of these and other plant pathogens on inert materials associated with movement of humans, farming equipment, and commodities nationally and internationally

Chemical treatments inhibiting germination of wheat rust, clover anthracnose, canola blackleg and rice blast spores

In vitro studies were undertaken to determine the effects of five chemical fungicide/disinfectant treatments [Tilt 250 EC (propiconazole), Amistar 250 SC (azoxystrobin), Sporekill, (didecyl dimethyl ammonium chloride), Farmcleanse (Alkali metal salts of alkylbenzene sulfonic acid and coconut diethanolamide) and Virkon S (potassium peroxymonosulfate)] in preventing spore germination of Puccinia graminis f. sp. tritici, Kabatiella caulivora, Leptosphaeria maculans and Magnaporthe oryzae. Germination was inhibited by all fungicides and disinfectants. Maximum reductions in spore germination were obtained at manufacturer’s recommended concentration and concentrations above, while concentrations below were less effective than the recommended concentration. Overall, Amistar and Tilt were the most effective of the chemicals tested, reducing germination of M. oryzae L. maculans and P. graminis f. sp. tritici spores by >75%. However, the extent to which germination of fungal spores was inhibited was dependent on the pathogen. Sporekill was the least effective, inhibiting spore germination across all the pathogens by <15%. Additional studies undertaken to define the effectiveness of the same fungicides/disinfectants for the same pathogens inoculated on five common carrier materials, metal, fabric, wood, paper, and rubber, also showed Amistar and Tilt the most effective. Results highlight a necessity for re-evaluating the requirement for decontamination procedures for carrier materials that have perhaps long been mistakenly considered of low biosecurity risk in regards to the movement of exotic fungal plant pathogens and their races

Inert materials as Long-Term carriers and disseminators of viable leptosphaeria maculans ascospores and wider implications for ascomycete pathogens

The viability of ascospores of the Phoma stem canker (blackleg) pathogen, Leptosphaeria maculans, was tested on a range of carrier materials, including metals, fabrics, woods, and plastics, and under different temperature conditions of 23 and 4, 36 and 14, and 45 and 15°C day and night, respectively. At 23 and 4°C (day and night, respectively), ascospores remained viable for up to 240 days on Tasmanian oak (Eucalyptus regnans) and pine wood (Pinus radiata). At 36 and 14°C (day and night, respectively), ascospores remained viable on pine wood for up to 180 days. At 45 and 15°C (day and night, respectively), ascospores remained viable up to 60 days on jute. There were also significant differences (P < 0.001) between carrier materials in their abilities to retain ascospores following washing. At least 30% of intact ascospores recovered from inert carrier materials were able to germinate on artificial growth media within 48 h of recovery and some ascospores were still viable after 240 days. These findings confirm that L. maculans ascospores remain viable for a much longer time in the absence of a host than previously considered. This demonstrates the importance of inert materials as long-term and long-distance carriers of viable L. maculans ascospores, and highlights their potential role for spread of L. maculans races to new regions and countries via farming equipment, clothing, and other associated materials. Local, national, and international biosecurity agencies need to be aware that the risks of spread of ascomycete plant, animal, and human pathogens via inert materials are significantly greater than currently assessed