Seed contaminants: an overlooked pathway for the introduction of non-native plants in Sardinia (Italy)

The accidental introduction of alien plants through contaminated seed is a source of new incursions and subsequent invasions that can impact natural habitats, agriculture and forestry. While seed lots for agricultural crops are often well regulated through a certification process, the trade of many other types of seeds is largely unregulated. Here, we evaluate the risk of seed lots trade as a pathway for invasive alien plant species in Sardinia (Italy), by identifying and quantifying the presence of contaminant species. The study included uncertified commercial seeds as well as the ones sold as pet feed. We randomly sampled 39 seed packets, from multiple sources, including novel forage crops under experimental testing (Fc), flower mixtures (Fm), recreational lawn mixtures (Lm) and pet feed (Pf). Germination and viability were analysed on the seed commodity of Pf. A total of 231 contaminant species was found, belonging to 88 genera and 34 families. Moreover, among the contaminants, the non-native invasive agricultural weeds Amaranthus sp. pl. and Echinochloa sp. pl. were found. Our results showed that unregulated seed contaminants are associated with a high risk of non-native plants entry and their potential establishment in Sardinia.