The import and export of tree seed carries with it risks of inadvertent introduction of pests and pathogens to hitherto unaffected regions. Although trade in seed of specified trees is regulated, phytosanitary requirements for most tree species are minimal, even those related to the most important forest tree species in a given region. A better understanding of the microbiome associated with seed intended for commercial production or ornamental use, and their potential risk with the transport from the source origin of distributors, will help regulatory agencies implement measures to safeguard seed health and avoid trade-related spread of potentially harmful pathogens. In this study we used high-throughput sequencing to show that highly diverse fungal communities were associated with seed of 14 different Pinus species obtained from seed banks (seed orchards) and retail sources (online distributors) in North America and Europe. Fungal diversity differed among the 23 seedlots tested. Community composition did not relate to the species of Pinus nor the country of origin. Assigned potential functions based on sequence identity using FUNGuild provided an overall understanding of the likely life strategies of fungal operational taxonomic units (OTUs). Of those sequences classified to a trophic level, 453 were plant pathogens, with the Dothideomycetes having the highest prevalence. The most common plant pathogens included Sydowia polyspora, Lasiodiplodia theobromae, Diplodia intermedia and Diplodia sapinea that were detected from the majority of Pinus species. The evidence presented here illustrates an urgent need for plant protection authorities, practitioners and the general public to recognize the potential risk of introducing harmful pathogens through innocent transport of seed.
The import and export of tree seed carries with it risks of inadvertent introduction of pests and pathogens to hitherto unaffected regions. Although trade in seed of specified trees is regulated, phytosanitary requirements for most tree species are minimal, even those related to the most important forest tree species in a given region. A better understanding of the microbiome associated with seed intended for commercial production or ornamental use, and their potential risk with the transport from the source origin of distributors, will help regulatory agencies implement measures to prevent new and emerging risks. In this study we used high throughput sequencing to show that highly diverse fungal communities were associated with seed of 14 different Pinus species obtained from seed banks (seed orchards) and retail sources (online distributors) in North America and Europe. Fungal diversity differed among the 23 seedlots tested. Community composition did not relate to the species of Pinus nor the country of origin. Assigned potential functions based on sequence identity using FUNGuild provided an overall understanding of the likely life strategies associated fungal OTUs. Of those sequences classified to a trophic level, 453 were plant pathogens, with the Dothideomycetes having the highest prevalence. The most common plant pathogens detected included Sydowia polyspora, Lasiodiplodia theobromae, Diplodia intermedia and Diplodia sapinea. The evidence presented here illustrates an urgent need for plant protection authorities, practitioners and the general public to recognize the potential risk of introducing harmful pathogens through innocent transport of seed.
In the past 25 to 30 years, a marked increase has occurred in numbers of invasive alien pests and pathogens recorded, damaging agriculture, horticulture and forest environments. The reasons for this upsurge are clear: all involve human-driven factors, with, arguably, global trade as the most important component in the complex. Climate change is another major factor. Each plant transported through trade could carry cryptic pests or pathogens, which may be introduced into previously naïve environments and lead to major health issues on previously unaffected plants. Global trade in plants is a complex system, driven by a desire to use large plants in landscapes and demand for varied species for gardens. Examples of invasive alien pathogens causing wide-spread problems on a global scale currently include many Phytophthora species, Dothistroma needle blight of pines, and Xylella fastidiosa on a wide range of trees. A striking example recently was the spread of the Dutch elm disease pathogen, Ophiostoma novo-ulmi, in North America and Western Europe. Many invasive pathogens cause problems in localized regions, including Ceratocystis platani, killing Platanus in some European countries. Other examples include the threat of pine wilt nematode (Bursaphelenchus xylophilus), damage to Cupressus in Mediterranean landscapes caused by Seiridium cardinale, dieback of sweet chestnut (Castanea) caused by the canker pathogen Cryphonectria parasitica, and many others. In addition to global trade, climate change appears to be exacerbating the problems, with major influences on establishment and spread of alien invasive species. Hope lies in the enormous genetic ‘power’ of plants: humans could establish selection and breeding programmes that will ultimately enable us to plant trees with greater tolerance of changing climate and pests and pathogens, whether native or invasive.
Non-native pests, climate change, and their interactions are likely to alter relationships between trees and tree-associated organisms with consequences for forest health. To understand and predict such changes, factors structuring tree-associated communities need to be determined. Here, we analysed the data consisting of records of insects and fungi collected from dormant twigs from 155 tree species at 51 botanical gardens or arboreta in 32 countries. Generalized dissimilarity models revealed similar relative importance of studied climatic, host-related and geographic factors on differences in tree-associated communities. Mean annual temperature, phylogenetic distance between hosts and geographic distance between locations were the major drivers of dissimilarities. The increasing importance of high temperatures on differences in studied communities indicate that climate change could affect tree-associated organisms directly and indirectly through host range shifts. Insect and fungal communities were more similar between closely related vs. distant hosts suggesting that host range shifts may facilitate the emergence of new pests. Moreover, dissimilarities among tree-associated communities increased with geographic distance indicating that human-mediated transport may serve as a pathway of the introductions of new pests. The results of this study highlight the need to limit the establishment of tree pests and increase the resilience of forest ecosystems to changes in climate.
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