Isolation of phloridzin-degrading, IAA-producing bacterium Ochrobactrum haematophilum and its effects on the apple replant soil environment

Abstract

We isolated and identified a bacterium that could produce IAA and degrade phloridzin in the rhizosphere soil of healthy replanted apple (the rootstock is M9T337 and the scion is Yanfu 3), providing a theoretical basis for reducing the obstacles associated with apple replant disease (ARD). Isolates were screened using Salkowski colorimetry and screening medium for phloridzin. The isolate of interest (W6) was identified as Ochrobactrum haematophilum based on morphological analysis, physiological and biochemical tests, and 16S rDNA sequencing. In a laboratory experiment, W6 produced auxin and promoted the growth of Arabidopsis thaliana roots, and its degradation rate of 100 mg · L−1 phloridzin was 62.0%. In a pot experiment, W6 significantly reduced the phenolic acid contents of replanted soil, lowered the abundance of the harmful fungus Fusarium solani, and increased soil enzyme activities, thereby improving the micro-ecological environment of replant soil. W6 increased the root antioxidant enzyme activity and leaf photosynthetic pigment content of replanted Malus hupehensis Rehd. seedlings, effectively alleviating the decrease in net photosynthetic rate, transpiration rate and stomatal conductance caused by ARD. In a field experiment, W6 also promoted the growth of replanted apple (the rootstock is M9T337 and the scion is Yanfu 3) saplings. Therefore, W6 can promote apple growth and degrade phenolic acids, and it can be used as an effective treatment for the reduction of ARD.