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Soil frequently occurs as a contaminant on numerous sea, land and air transport pathways. It can carry unwanted invasive species, is widely recognized as a biosecurity risk, and is usually strictly regulated by biosecurity authorities. However, little is known about relative risk levels between pathways, thus authorities have limited capability to identify and target the riskiest soil pathways for management. We conducted a an experiment to test the hypotheses that biosecurity risks from soil organisms will increase both with declining transport duration and with increasing protection from environmental extremes. Soil was collected from two sites, a native forest remnant and an orchard, and stored on, in and under sea containers, or in cupboards, and assayed after 0, 3, 6 and 12 months for bacteria, fungi, nematodes and seeds. Results showed that viability of Pseudomonas spp., bacteria, nematodes and plants declined over 12 months, irrespective of soil source. Also, mortality of most biota was higher when exposed to sunlight, moisture and desiccation than when protected. However, bacterial and fungal numbers were higher in exposed environments, possibly due to ongoing colonization of exposed soil by airborne propagules. The results were consistent with our observations of organisms in soil intercepted from airports and sea ports, and indicated there is potential to rank risks from transported soils based partly on transport duration and environmental exposure. This would help authorities to optimally allocate management resources according to pathway-specific risks.
Plant parasitic nematodes (PPN) are known to survive periods of desiccation, an ability that increases the risk of them surviving unintentional transport between countries. To investigate nematode survival in soil subject to prolonged storage, soil collected from a native forest and an organic orchard was stored separately in cupboards at ambient temperature for 36 months. Subsamples were taken at 0, 3, 6, 12, 13, 24 and 36 months to determine the presence of plant parasitic and total nematodes using a standard misting technique. Pratylenchus was used as a model to determine if PPNs that had been under prolonged storage were able to infect plant hosts at 13, 24 and 36 months. Overall, the total number of nematodes recovered from stored soil declined over time, with differences in species diversity determined by molecular methods, related to soil origin. No PPN were recovered in soil stored beyond 13 months using the three-day misting technique. By comparison, Pratylenchus nematodes, using a baiting method, were found to successfully invade host plant roots (ryegrass and white clover) even after 36 months storage and were observed to produce offspring at 13 months. Baiting was not effective for Pratylenchus found in soil originally collected from the forest but was for orchard soil, a result attributed to the lack of suitable host plants for the Pratylenchus species found in forest soil. This study demonstrated, that in protected environments, nematodes could survive for at least 36 months and were observed to produce offspring at 13 months. Baiting with a host plant was more sensitive in detecting nematodes than using the misting extraction technique, although this approach only works where the host plant is known. Without a priori knowledge of the nematode-plant host association, plant baiting may also produce false negatives. In the context of plant biosecurity and providing an accurate risk assessment in soil contaminants, the development of a generic test for PPN that induces nematodes in a resting stage to emerge and respond to a cue would enhance the probability of detection. However, as assessments at the border are often time limited, a molecular based bioassay that can be used to indicate the presence of multiple species of live PPN species may be a more feasible option for risk assessments.
Phenological studies are important to gain insights into the ecology of plant species, particularly those that are threatened and require specific management actions such as regular population monitoring. For many species of terrestrial orchids, limited fundamental knowledge on peak flowering, pollination and seed production restricts effective monitoring outcomes. In this single-season study, phenology data from one population of the vulnerable Diuris praecox were collected, with the aim of informing future management relating to monitoring surveys and to assist in conservation of this species. To this end, six sub-populations (three each in forest habitat and along maintained powerline easements) were visited weekly from the onset of flowering until seed release, with observations made on 134 tagged individuals within 10 x 10 m plots. During the 2019 flowering season, 37% of all plants developed capsules, and 35% released seed. However, success varied between locations, with greater floral displays along powerline easements resulting in stronger pollination rates, while sparse sub-populations in forested locations showed lower pollination. Significantly more flowers per inflorescence (range 1-7) were evident in forest than easement sites, but there was no significant difference in inflorescence height across these habitats. For most sub-populations at least one orchid set seed, even when occurring in low densities (<10 plants). Overall, substantial floral displays did not necessarily result in abundant fruiting, and impacts from desiccation, predation and grazing likely prevented more successful capsule production in any given sub-population. The synchronously flowering shrubs Daviesia ulicifolia and Pultenaea villosa co-occurred across all sub-populations, suggesting that the nectar-less Diuris praecox may mimic these species to attract pollinators. Peak flowering was determined to be approximately 20 days from the onset of flowering, with 83% of all plants in flower at that time. For ongoing monitoring, the timing of surveys to occur approximately three weeks after the first observed flowering, will likely maximize return-for-effort, particularly when survey resources are limited, although it is acknowledged that different seasons and populations may vary from this timeframe.