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

Abstract

The international seed trade is considered relatively safe from a phytosanitary point of view and is therefore less regulated than trade in other plants for planting. However, the pests carried by traded seeds are not well known. We assessed insects and fungi in 58 traded seed lots of 11 gymnosperm and angiosperm tree species from North America, Europe, and Asia. Insects were detected by X‐raying and molecular methods. The fungal community was characterized using high‐throughput sequencing (HTS) and by growing fungi on non‐selective agar. 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 (Curculio spp.) larvae. HTS indicated the presence of fungi in all seed lots and fungi grew on non‐selective agar from 96% of the seed lots. Fungal abundance and diversity were much higher than insect diversity and abundance, especially in angiosperm seeds. Almost 50% of all fungal exact sequence variants (ESVs) found in angiosperms were potential pathogens, in comparison with around 30% of potentially pathogenic ESVs found in gymnosperms. The results of this study indicate that seeds may pose a greater risk of pest introduction than previously believed or accounted for. A rapid risk assessment suggests that only a small number of species identified in this study is of phytosanitary concern. However, more research is needed to enable better risk assessment, especially to increase knowledge about the potential for transmission of fungi to seedlings and the host range and impact of identified species.

Spotting the pests of tomorrow—Sampling designs for detection of species associations with woody plants

“…This is especially relevant for insect pests, as if they have left the plants then they are no longer at risk of being transported with the plants (e.g. Franić et al, ).…”

“…The fungal community was assessed for 100 surface sterilized seeds each from six locations by growing fungi on non‐selective agar media (1.5% water agar (PPA, Pronadisa Lab. Conda) with streptomycin (100 mg/L) to inhibit bacterial growth) and grouping the obtained isolates based on their morphology (Franić et al, ). The diversity of fungal morphotypes in each sample was assessed by calculating rarefaction (interpolation) and extrapolation (prediction) of sampling curves.…”

Fast and reliable molecular methods to detect fungal pathogens in woody plants

“…To address this gap in our knowledge, one of the most challenging fields in plant health is the identification of potential threats before their introduction in a new environment. The trade in forest tree seeds is therefore considered to be high risk for the introduction of fungal pathogen in disease-free areas (Burgess and Wingfield 2002;Franić et al 2019), and sensitive tests are required to check their health status before movement (Ioos et al 2009a;Lamarche et al 2015). Sentinel planting, i.e., plants native to importing country planted in exporting countries that are inspected and analyzed at regular intervals for microbial pathogen detection, is the most promising tool (Eschen et al 2019).…”

Strategies for deployment of reproductive material under supply limitations – a case study of Norway spruce seed sources in Sweden

“…In case this is not possible trees with lower performance have to be used which in turn yields lower growth and quality (Liziniewicz and Berlin 2019;Haapanen, 2020). The nonnative seeds can also be a potential source of nonnative pests, which needs to be considered when importing material from other countries (Franić et al 2019). Another aspect of this is how the climate will change in the future where local trees will not be able to disperse, establish or adapt as fast as needed.…”