Exploited mutualism: the reciprocal effects of plant parasitic nematodes on the mechanisms underpinning plant-mutualist interactions.

We are quickly gaining insights into the mechanisms and functions of plant-mutualist relationships with the common overarching aim of exploiting them to enhance food security and crop resilience. There is a growing mass of research describing various benefits of plant-mutualistic fungi, including increased nutrition, yields, and tolerance to biotic and abiotic factors. The bulk of this research has been focused on arbuscular mycorrhiza; however, there is now an expansion toward other plant mutualistic fungi. Contrary to the established 'mycorrhizal induced resistance' principle, increasing evidence shows that certain plant pests and pathogens may, in fact, exploit the benefits that mutualists provide their hosts, resulting in enhanced pathogenicity and reduced mutualist-derived benefits. In this Viewpoint, we propose that studying plant mutualistic fungi under controlled artificial conditions indeed provides in-depth knowledge but may mislead long-term applications as it does not accurately reflect multi-symbiont scenarios that occur in natura. We summarize the reciprocal impacts of plant pests, such as plant parasitic nematodes, on plant-fungal mutualisms and highlight how glasshouse experiments often yield contradictory results. We emphasize the need for collaborative efforts to increase the granularity of experimental systems, better reflecting natural environments to gain holistic insights into mutualist functions before applying them in sustainable crop protection strategies.