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.
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.
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.
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