Improving apple orchard health: The role of arbuscular mycorrhizal fungi in alleviating replant disease and strengthening soil microbial communities

The occurrence of apple replant disease (ARD) is inevitable during the renewal and transformation of aging orchards. This disease seriously threatens the healthy and sustainable development of the apple industry. Arbuscular mycorrhizal fungi (AMF) have shown great potential in promoting plant growth, resisting soilpathogen infection and improving soil quality. However, there is relatively little information available about the application of AMF in the prevention and control of ARD. In this study, we conducted a pot and field experiment were conducted with inoculation of AMF (Paraglomus sp. SW1) on apple rootstock (Malus hupehensis Rehd. in the pot experiment and M9T337 in the field experiment) to explore the biocontrol effect of AMF on ARD by comparing the changes in fungal and AMF communities after AMF inoculation on apples under replanting conditions. AMF-inoculated apple was used as the treatment, while non-inoculated apple was used as the control. The results showed that AMF-inoculated plants not only promoted the growth of M. hupehensis Rehd., but also stimulated the branch elongation growth of young apple trees, compared to the control. After inoculation with AMF, the community structure of soil fungi and arbuscular mycorrhizal fungi changed significantly, with an increase in the abundance of fungi and AMF in soil, and a significant reduction in the abundance of Fusarium spp., especially Fusarium moniliforme, Fusarium solani, and Fusarium proliferatum. Additionally, the soil enzyme activity increased significantly. Furthermore, the levels of ammonium nitrogen (NH4+), nitrate nitrogen (NO3-), available phosphorus (AP), available potassium (AK), organic matter (SOM), and pH in the rhizosphere soil were significantly related to the changes in the community structure of fungi and AMF. The AP, NH4+ and NO3- was found to drive the fungal communities, while NH4+ and NO3- drove the AM fungal communities in replanting soil. In conclusion, apple-arbuscular mycorrhizal symbionts can effectively alleviate ARD by promoting plant growth and optimizing the structure of soil microbial communities. Future research, should test other gardening plants following AMF inoculation to prepare for a wider application in controlling replant disease.