Rhizobia mitigates autotoxicity in Malus hupehensis via phenolic degradation and enhanced melatonin-antioxidant responses

Abstract

Introduction Phloridzin is a major autotoxin contributing to apple replant disease (ARD) by inducing oxidative stress and disrupting the rhizosphere ecology. Methods This study evaluated the potential of Ensifer meliloti y5077 to mitigate these detrimental effects in Malus hupehensis. Results Strain y5077 demonstrated high degradation efficiency, removing 100% of phloridzin in vitro within 48 h and reducing soil phloridzin levels by 68.4% in 60-day pot experiments. Inoculation significantly improved seedling growth under autotoxic stress, with root dry weight increased compared to non-inoculated stressed plants. These growth benefits were linked to a significant increase in endogenous melatonin levels and the restoration of antioxidant enzyme activities to normal basal levels, which effectively suppressed malondialdehyde (MDA) and reactive oxygen species (ROS) accumulation. Furthermore, y5077 inoculation restructured the rhizosphere microbiome, characterized by significant shifts in the relative abundance of specific microbial taxa (e.g., increases in Firmicutes and Actinobacteriota, and decreases in Basidiomycota). Discussion These results demonstrate that y5077 acts as a multi-functional bioremediator that integrates toxin degradation with physiological priming and rhizosphere microbial community restructuring, providing a robust and sustainable biological solution for mitigating phloridzin-induced autotoxic stress in apple seedlings.