Plant parasitic nematode survival and detection to inform biosecurity risk assessment

Abstract

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. Aalders et al. / NeoBiota 36: 1-16 (2017) 2

Quantifying the economic cost of invertebrate pests to New Zealand’s pastoral industry

“…Pratylenchus is observed in >90% of pasture soil samples throughout New Zealand (Yeates 1981;Skipp & Christensen 1983;Knight 2001;McNeill et al 2015) and large populations have been associated with a lack of plant response to applied fertilisers (Yeates 1976). Some Pratylenchus species are able to withstand long periods of desiccation (Das Neves et al 2012;Aalders et al 2017), which probably assists their ability to persist in most soil situations. Heterodera populations occur throughout the country and in both lowland and hill country situations (Skipp and Christensen 1983;Mercer and Woodfield 1986).…”

Potential distribution and biosecurity risks from three economically important plant‐parasitic nematodes

“…In addition to local spread in irrigation water, dispersal of H. zeae is aided by its survival for long periods in the absence of hosts. Viability for 3-7 years under transit conditions has been observed (Aalders, McNeill, Bell, & Cameron, 2017).…”

Assessment of Common Factors Associated with Droplet Digital PCR (ddPCR) Quantification of Paratrichodorus allius in Soil

“…Nematodes were rapidly killed in freezing temperatures [ 27 ] and above 20 °C [ 30 ]. Interestingly, Pratylenchus species, one of the common PPNs, were found to be infective even after 36 months of storage at 12.5 °C [ 26 ]. Whether nematodes are dead or alive in stored soil, the molecular analysis of nematodes in soil should not be affected substantially by the physical conditions of the nematodes since DNA from both dead and live nematodes would be accounted for in the analysis.…”

“…Thus, the storage time may not directly influence the molecular analysis of soil, but other environmental factors may, such as soil pH, soil type, vegetation, and soil handling before storage [ 45 ]. In all studies with PPNs, nematode numbers gradually decreased over time even at the optimal storage temperature [ 26 , 27 , 28 , 31 ]. In a proteomic study with entomogenic nematodes at two storage temperatures (9 °C and 20 °C), it was found that the proteome of the nematodes was affected by temperature, as well as nematode species [ 46 ].…”

“…Many PPNs can tolerate periods of desiccation. Previous studies have demonstrated that soil samples intended for nematode analysis can be stored at 5–20 °C for a considerable length of time with the optimum storage temperature being 10–15 °C [ 26 , 27 ]. However, nematode recovery percentage decreases with time regardless of the storage temperature [ 28 ].…”