Investigating the effect of microbial inoculants Frankia F1 on growth-promotion, rhizosphere soil physicochemical properties, and bacterial community of ginseng

Abstract

Ginseng root rot caused by Fusarium solani (F. solani) is a highly destructive soil-borne disease that happens worldwide, which seriously affects the growth and development of many types of crops. Frankia casuarinae CcI3 (Frankia F1) microbial inoculants F1 on the mycelial integrity of pathogenic fungus F. solani, the growth of ginseng plants, and the structure of rhizosphere microbial community were carefully studied in the rhizosphere soil of ginseng infected with ginseng disease. Under the normal ginseng growth and F. solani infected environment, plant height, root length, dry weight, stem diameter, leaf area, and chlorophyll content increased by 40.57%, 68.98%, 92.09%, 56.67%, 23.29%, and 39.60% in T2 (50 mL microbial inoculants F1) compared with CK (natural control without treatment). Increased enzyme activity of phenylalanine ammonia-lyase (PAL), peroxidase (POD), polyphenol oxidase (PPO), β-1, 3-glucanase, and chitinase showed improved disease resistance and stress resistance of plants in ginseng leaves having inoculation. Our present study demonstrated that the soil pH value, cation exchange capacity, organic matter, total nitrogen, available nitrogen, phosphorus, and potassium increased by 8.00%, 50.78%, 18.81%, 43.36%, 23.25%, 14.00%, and 5.11% in T2 compared with CK. Furthermore, the soil enzyme activities of catalase, sucrase, and urease in T2 treatment were increased by 12.14%, 27.56%, and 22.60%, respectively. Amplicon sequencing analysis revealed that the diversity of soil bacteria decreased after microbial inoculants F1 treatment. More specifically, the T2 treatment inhibited the growth of F. solani, and promoted that the relative abundance of Xanthomonadales, Sphingomonadales, Sphingobacteriales, Frankiales, and Propionibacteriales. The PICRUSt data predicted an array of bacterial functions, and microbial inoculants F1 primarily increased the abundance of functional genes related to bacterial metabolism in ginseng soil we confirmed. Collectively, we found that the optimal inoculation amount of Frankia F1 for inhibiting F. solani and promoting the growth of ginseng plants was 50 mL (T2), which could effectively regulate the soil microbial community structure during ginseng production. It helped to promote the sustainable development of Chinese agriculture.