Arbuscular mycorrhizal fungi alleviate pathogenic stress on the invasive weed Alternanthera philoxeroides

Context Invasive plants can cause extensive damage in ecosystems. The ‘enemy release hypothesis’ proposes that invasive plants often escape from their natural enemies including pathogens. Arbuscular mycorrhizal fungi (AMF) play important roles in plant growth; however, the importance of AMF in pathogenic stress on invasive plants has rarely been studied. Aims The effects of AMF (Claroideoglomus etunicatum) on resistance of an invasive plant Alternanthera philoxeroides to the pathogenic fungus Rhizoctonia solani were examined in a 2-month greenhouse experiment, using four treatments (with/without AMF inoculation × with/without pathogen infection). Key results The AMF colonisation rates increased significantly in the presence of R. solani. The AMF significantly promoted stem length, spacer length, and leaf area of A. philoxeroides. The pathogen R. solani negatively impacted plant growth, including aboveground biomass and root characteristics; however, AMF inoculation mitigated these negative effects. The AMF significantly promoted aboveground growth and decreased the root/shoot ratio, helping to resist the pathogen. Conclusions These findings indicate that AMF can enhance A. philoxeroides resistance to pathogenic stress, potentially contributing to its invasive success. Implications This study provides insights into the interactions between invasive plants, beneficial fungi, and pathogens, which may have implications for understanding and managing plant invasions. Disrupting the AMF symbiosis might improve the control efficiency of invasive plants.