Arbuscular mycorrhizal fungi travel the world with harvested underground crops

In recent years, the dispersal of potentially invasive plants, animals, and pathogens via international trading routes for fresh agricultural goods has been the subject of intensive research and risk assessment. Comparatively little is known about the potential impact of global food trade on the spreading of symbiotic soil microorganisms, such as arbuscular mycorrhizal (AM) fungi. The present study thus assessed whether internationally traded underground crop harvest products carry AM fungal propagules. Twenty batches of tubers, corms or bulbs originating from eight different countries were sampled and used to inoculate Sorghum bicolor (L.) Moench plants grown in a heat-sterilized, sandy dune soil from the United Arab Emirates (UAE). Results revealed that most of the underground crop harvest products contained AM fungal propagules able to establish AM symbioses in a pot experiment under greenhouse conditions. Though it is likely that most AM fungal propagules attached to harvest products will ultimately be eliminated in the waste or sewage stream, it is well possible that a certain portion would find its way into agricultural or natural ecosystems, e.g., via organic waste disposal or use of kitchen greywater for irrigation. Given the large volumes of underground crops traded worldwide, their impact on AM fungal dispersal and distribution deserves further investigation and assessment of associated risks of adulteration of soil microbial communities.