Weed seed contamination in imported seed lots entering New Zealand

Abstract

Imports of seeds for sowing are a major pathway for the introduction of contaminant seeds, and many agricultural weeds globally naturalised originally have entered through this pathway. Effective management of this pathway is a significant means of reducing future plant introductions and helps minimise agricultural losses. Using a national border inspection database, we examined the frequency, origin and identity of contaminant seeds within seed for sowing shipments entering New Zealand between 2014–2018. Our analysis looked at 41,610 seed lots across 1,420 crop seed species from over 90 countries. Overall, contamination was rare, occurring in 1.9% of all seed lots. Among the different crop types, the arable category had the lowest percentage of seed lots contaminated (0.5%) and the forage category had the highest (12.6%). Crop seeds Capsicum, Phaseolus and Solanum had the lowest contamination rates (0.0%). Forage crops Medicago (27.3%) and Trifolium (19.8%) had the highest contamination rates. Out of 191 genera recorded as contaminants, Chenopodium was the most common. Regulated quarantine weeds were the rarest contaminant type, only occurring in 0.06% of seed lots. Sorghum halepense was the most common quarantine species and was only found in vegetable seed lots. Vegetable crop seed lots accounted for approximately half of all quarantine species detections, Raphanus sativus being the most contaminated vegetable crop. Larger seed lots were significantly more contaminated and more likely to contain a quarantine species than smaller seed lots. These findings support International Seed Testing Association rules on maximum seed lot weights. Low contamination rates suggest industry practices are effective in minimising contaminant seeds. Considering New Zealand inspects every imported seed lot, utilises a working sample size 5 times larger than International Seed Testing Association rules require, trades crop seed with approximately half of the world’s countries and imports thousands of crop seed species, our study provides a unique overview of contaminant seeds that move throughout the seed for sowing system.

Translating virome analyses to support biosecurity, on-farm management, and crop breeding

“…Australia and New Zealand, island nations with unique endemic biota, apply stringent biosecurity practices to reduce catastrophic introductions of invasive species ( Simberloff, 2019 ; Pysek et al., 2020 ). New Zealand has an effective seed screening protocol with only an estimated 1.9% of lots being contaminated, but containing over 190 genera of weeds ( Rubenstein et al., 2021 ), where weed seed also has the potential to introduce new viruses detrimental to crop production or natural plant systems. Virus screening in Australia employs a combination of visual methods, bioassays, ELISA, PCR and qPCR approaches, in which thresholds for acceptable viral contamination are determined through a regularly adjusted ‘appropriate level of protection’ evaluation ( Whattam et al., 2021 ).…”

“…only an estimated 1.9% of lots being contaminated, but containing over 190 genera of weeds (Rubenstein et al, 2021), where weed seed also has the potential to introduce new viruses detrimental to crop production or natural plant systems. Virus screening in Australia employs a combination of visual methods, bioassays, ELISA, PCR and qPCR approaches, in which thresholds for acceptable viral contamination are determined through a regularly adjusted 'appropriate level of protection' evaluation (Whattam et al, 2021).…”

Factors impacting the detection of weed seed contaminants in seed lots

“… 1 , 10 However, as a global commodity, contaminated seed for sowing can provide a pathway for the introduction and establishment of pests, weeds and diseases with the potential to cause unwanted impacts across field, farm, regional or national scales. 1 , 2 , 3 These unintended introductions contribute to the homogenization of world floras and are a threat to global food security. Mitigating the impacts of weeds, pests, diseases or other invasive species in seed‐for‐sowing systems is a shared goal of farmers, seed producers and national/international plant protection organizations.…”

“… 11 , 12 Detections of new seeds of concern at the border prior to clearance in New Zealand, are rare, given the high inspection rates, with seed cleaning and inspections occurring offshore prior to shipment, and on arrival in New Zealand. 2 , 10 Post‐border incursions ( i.e ., detection of newly imported regulated weeds growing in fields New Zealand) are also rare. 2 , 10 It is possible that seed importers are taking extra steps to reduce seed contaminants to avoid problems (such as costly destruction or reshipping) due to the high inspection rates at the New Zealand border for seeds for sowing imported into New Zealand.…”

“… 2 , 10 Post‐border incursions ( i.e ., detection of newly imported regulated weeds growing in fields New Zealand) are also rare. 2 , 10 It is possible that seed importers are taking extra steps to reduce seed contaminants to avoid problems (such as costly destruction or reshipping) due to the high inspection rates at the New Zealand border for seeds for sowing imported into New Zealand.…”