Establishment of rapid propagation system of high-essential-oil Melaleuca alternifolia and characteristics of soil microorganisms during plantlet transitioning from aseptic to microorganism conditions

Plant tissue culture is a valuable tool for the asexual propagation of valuable genotypes, enabling the conversion of tissue-cultured plantlets from a closed sterile environment to a natural environment, however, the influence of tissue-cultured plantlets on the characteristics of soil microbial communities during their gradual adaptation to the environment is still unknown. This study established a rapid propagation system for 4-terpineol type Melaleuca alternifolia and analyzed the changes in soil microbial community composition after transplanting tissue-cultured plantlets. The optimal formulation for proliferation was 1/2MS + 0.3 mg/L 6-BA + 30 g/L sucrose, and the average multiplicity was 4.04. The optimal rooting medium was 1/4MS + 0.7 mg/L IBA + 0.7 g/L AC + 25 g/L sucrose, and the rooting rate was 100 %. In the initial adaptation stage (40 d), the rhizosphere soil microorganisms of the tissue-cultured plantlets were characterized by drastic changes in the relative abundances of fungal genera greater than 10 % and a stable composition of bacterial genera, whereas in the complete adaptation stage (150 d), the number of dominant fungal genera with relative abundance of greater than 10 % increased, and the composition of the dominant bacterial genera remained stable. Throughout 4-terpineol type M. alternifolia domestication, the fungal genera with more than 10 % relative abundance changed, and the composition of the top 10 bacterial genera in terms of relative abundance was stable. The increase in the relative abundances of the beneficial bacterial genera Bradyrhizobium and Mesorhizobium, and the relative abundances of phytopathogenic fungi Fusarium and Colletotrichum decreased, may be related to the root exudates of 4-terpineol type M. alternifolia. The paper not only presents a rapid plant propagation system suitable for commercial use but also establishes a scientific foundation for the utilization of beneficial microorganisms to enhance the overall health of soil-plant systems.