Non-Host Status of Brassicaceae Plants to Mucoromycotina Fine Root Endophytes and Their Neutral Impact on Neighboring Host Mycorrhiza and Phosphorus Uptake

Brassicaceae plants are generally considered non-mycorrhizal; however, recent studies have challenged this non-host status, suggesting occasional colonization during reproductive stages or by overlooked fungi such as Mucoromycotina Fine Root Endophytes (MFRE). To re-evaluate the non-host status of Brassicaceae, we cultivated five Brassicaceae species, including rapid life cycle Brassica rapa (Fast plants) using field soil containing both Glomeromycotina Arbuscular Mycorrhizal Fungi (G-AMF) and MFRE. To ensure inoculum potential, a co-planting system with lettuce (Lactuca sativa) as a nurse plant was employed. While lettuce roots were rapidly colonized by both G-AMF and MFRE, no mycorrhizal colonization was observed in any Brassicaceae roots throughout their entire life cycle, from vegetative growth to flowering and seed maturation in Fast plants. Furthermore, co-planting with Brassicaceae did not significantly affect the mycorrhizal colonization or shoot phosphorus concentrations of the neighboring lettuce. These results demonstrate that Brassicaceae plants maintain a robust non-host status against both G-AMF and MFRE. Moreover, they function as “neutral non-hosts” that do not disrupt the symbiotic networks of neighboring plants. This characteristic reinforces the value of Brassicaceae in sustainable crop rotation systems.