Are traded forest tree seeds a potential source of nonnative pests?

Authors: FRANIC, IVA - Centre For Agriculture & Biosciences International (CABI); PROSPERO, S - Swiss Federal Research Institute Wsl; HARTMANN, MARTIN - Eth Zurich; ALLAN, ERIC - University Of Bern; AUGER-ROZENBERG, MARIE-ANNE - Institut National De La Recherche Agronomique (INRA); Grunwald, Niklaus - Nik; KENIS, MARC - Centre For Agriculture & Biosciences International (CABI); ROQUES, ALAIN - Institut National De La Recherche Agronomique (INRA); SCHNEIDER, SALOME - Swiss Federal Research Institute Wsl; SNIEZKO, RICHARD - Us Forest Service (FS); WILLIAMS, WYATT - Oregon Department Of Forestry; ESCHEN, RENE - Centre For Agriculture & Biosciences International (CABI)

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2019
Publication Date: 7/13/2019
Citation: Franic, I., Prospero, S., Hartmann, M., Allan, E., Auger-Rozenberg, M., Grunwald, N.J., Kenis, M., Roques, A., Schneider, S., Sniezko, R., Williams, W., Eschen, R. 2019. Are traded forest tree seeds a potential source of nonnative pests? Ecological Applications. 29(7). https://doi.org/10.1002/eap.1971.
DOI: https://doi.org/10.1002/eap.1971

Interpretive Summary: International seed trade is considered relatively safe from the phytosanitary point of view, compared with the trade in other plants for planting (P4P), and is thus less regulated. The pests potentially carried by seeds are, however, not well known and additional knowledge would be valuable. We assessed insects and fungi in 58 traded seed lots, 100 seeds each, of eleven tree species from North America, Europe and China. Insects were detected by x-raying, extracted and identified by sequencing DNA. The fungal community was characterized sequencing DNA extracted from each seed lot, and by growing fungi from seeds on growth media, grouping them according to morphology and sequencing a few representatives of each morphological group. Our results provide evidence for the movement of pests previously undetected from the studied countries. Although rare compared to fungi, insects representing a phytosanitary risk were more frequent in naked-seed plant seeds and were more specific. Fungal abundance and diversity were much higher, especially in flowering plant seeds which also contained more fungi capable of causing disease than naked-seed plant seeds. Moreover, seeds from Asia contained large fractions of disease-causing and unique fungi. The presence of pests in traded tree seeds highlights the need for measures to mitigate the risk of introducing new pests and repeated introduction of known pests.

Technical Abstract: International seed trade is considered relatively safe from the phytosanitary point of view, compared with the trade in other plants for planting (P4P), and is thus less regulated. The pests potentially carried by seeds are, however, not well known and additional knowledge would be valuable. We assessed insects and fungi in 58 traded seed lots, 100 seeds each, of eleven tree species from North America, Europe and China. Insects were detected by x-raying, extracted and identified by sequencing the mtDNA COI region. The fungal community was characterised using high-throughput sequencing (HTS) of DNA extracted from each seed lot, and by growing fungi from seeds on non-selective agar, grouping them according to culture morphology and sequencing a few representatives of each morphotype. Fungi were identified by sequencing the rDNA ITS2 region. About 30% of the seed lots contained insect larvae. Gymnosperms contained mostly hymenopteran (Megastigmus spp.) and dipteran (Cecidomyiidae) larvae, while angiosperms contained lepidopteran (Cydia latiferreana) and coleopteran larvae. HTS revealed fungi in all seed lots and fungi grew on non-selective agar from 96% of the seed lots. The results provide evidence for the movement of pests previously undetected the studied countries. Although rare compared to fungi, insects representing a phytosanitary risk were more frequent in gymnosperm seeds and were more specific. Fungal abundance and diversity were much higher, especially in angiosperm seeds which also contained more pathogenic fungi than gymnosperm seeds. Moreover, seeds from Asia (China) contained large fractions of pathogenic and unique fungi. The presence of pests in traded tree seeds highlights the need for measures to mitigate the risk of introducing new pests and repeated introduction of known pests. Different patterns in insect and fungal abundance and diversity suggest that the whole picture needs to be considered when assessing the phytosanitary risk.