The role of weed seed contamination in grain commodities as propagule pressure

Abstract

The international grain trade is a major pathway for the introduction of alien plants because grain commodities can be contaminated with various weed seeds. To evaluate how alien weed seeds derived from imported grain commodities affect local vegetation in international trading ports, we conducted a vegetation survey on a set of grain landing ports and non-grain landing ports in nine regions throughout Japan to compare the vegetation between these two types of ports. We also surveyed weed seed contamination of wheat imported into Japan, and the contamination rate was calculated for each species based on our survey and previous studies on weed seed contamination. The vegetation clearly differed between the grain landing ports and the non-grain ports. In the grain landing ports, alien species were more abundant than in non-grain landing ports. All indicator species of the grain landing ports were reported to be contaminants in grain commodities. Furthermore, there was a tendency for the more abundant species at the grain landing ports to show higher contamination rates in grain commodities.These results indicate that contaminant seeds spill from imported grain in grain landing ports, and highly contaminated species are likely to become established. We clearly show that weed seed contamination in grain commodities plays an important role in propagule pressure. Gathering information about the prevalence of weeds in grain-exporting countries and monitoring the weed species composition in imported grain commodities is becoming increasingly important for predicting the unintentional introduction of troublesome weeds and identifying effective weed management options.

Agricultural weeds: the contribution of domesticated species to the origin and evolution of feral weeds

“…4,82 Consequently, gene flow between crops (or volunteer plants) and their wild or weedy relatives may lead to the introgression of desired crop traits in wild/ weedy populations, and thus result in the evolution of new weeds or enhance the weediness of existing weeds (more problematic weeds), referred to as "superweeds". 4,83 In addition, given that seeds of cultivated species could be intentionally or unintentionally dispersed away from the production areas, 17,18 superweeds may emerge in those countries where desired crop traits have been permitted legally or in those where they have not. 82,84,85 For example, Pandolfo et al 8 found transgenic glyphosate-resistant oilseed rape in Argentina where it has never been permitted legally.…”

“…Alien species are introduced intentionally (for example, for cultivation, breeding, and research) or accidentally (for example, as contaminants of traded goods) outside their native range through global commerce 17 . Internationally traded seed and grain are two of the main pathways for the introduction of weed seeds into new areas 17,18 . So, weeds can be problematic in their native range (“native weeds”) and/or colonize new habitats and become “invasive weeds”.…”

“…17 Internationally traded seed and grain are two of the main pathways for the introduction of weed seeds into new areas. 17,18 So, weeds can be problematic in their native range ("native weeds") and/or colonize new habitats and become "invasive weeds". In a new habitat, roads or railways function as corridors for invasive species-inadvertently transported by vehicles, agricultural equipment, people and animals-providing suitable disturbed habitats for their establishment and spread.…”

Factors impacting the detection of weed seed contaminants in seed lots

“…Seeds are a key agricultural input and output and are a part of a complex global trade network 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 1–3 . These unintended introductions contribute to the homogenization of world floras and are a threat to global food security.…”

“… 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.…”