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.
Highlights
Seed for sowing shipments provide a major pathway for weed seed contaminants across the globe [1–4]
This study aims to help inform Ministry for Primary Industries (MPI) and industry by determining 1) the most and least contaminated crop types and crop seeds entering New Zealand, including corresponding contamination rates; 2a) the most common contaminant seeds; 2b) the most common category of contaminant seed; 2c) which crop seed, crop type and exporting country are most commonly associated with a regulated quarantine weed, and; 3) whether the size of a seed lot is linked to contamination
Past international studies looking at weed seed contamination are scarce, and generally focused on relatively few crop species or a small number of seed lots [2, 6, 54, 55]
Summary
Seed for sowing shipments (hereafter referred to as a seed lot) provide a major pathway for weed seed contaminants across the globe [1–4]. While economically beneficial to local industry, increases in the number of imported crop species, trading partners and trade volume provide more pathways for the introduction of non-native plant species, thereby raising the probability of introducing new weed species that threaten crop production and raise management costs [16, 17]. Management of this pathway is a significant means of reducing future plant invasions [18]
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