Isolation of Dominant Actinomycetes from Soil of Waxberry Orchards and Its Disease Prevention and Growth-Promotion Function

Abstract

[Objective]The objective of this study is to isolate and screen the dominant actinomycetes from plant roots and rhizosphere soils in waxberry orchards, explore the seasonal characteristics of the number and distribution of actinomycete populations, and to analyze its application potential in biological control and plant growth promotion.[Method]Samples of plant roots and rhizosphere soils were collected in different seasons from waxberry orchards, and the dominant actinomycetes were isolated and purified by the dilution plate method. Selective media were used to analyze the plant growth-promoting rhizobacteria (PGPR) characteristics of dominant actinomycetes such as nitrogen fixation, phosphorus solubilization, and potassium solubilization. The CAS plate assay was used to detect siderophore production capacity. The Salkowski assay was used to detect IAA production capacity. The colorimetric method was used to detect ACC deaminase activity. The strains with excellent growth-promoting characteristics were identified by test tubes for pro-biogenesis, and their antibacterial activity was analyzed by the flat-confrontation method and the Oxford cup method. Finally, the taxonomic status of the strain with good characteristics was identified by morphological observation, physiological and biochemical tests, and 16S rDNA sequence analysis.[Result]A total of 127 strains of dominant actinomycetes were isolated from two waxberry orchards at different altitudes, including 32 from plant roots and 95 from rhizosphere soils. Compared with those isolated in spring and summer, the actinomycetes isolated in autumn and winter had greater quantity and variety, stronger inhibition and promotion ability. The number of dominant actinomycetes isolated at higher altitudes was significantly higher than at lower altitudes in spring and summer, while in autumn and winter the number of actinomycetes isolated at lower altitudes exceeded that of higher altitudes and far exceeded the total number of actinomycetes isolated in spring and summer in that area. Finally, 46 strains of different species of actinomycetes were obtained, and through the analysis of PGPR characteristics, 35 strains of actinomycetes had obvious growth-promoting characteristics. Among them, strain Sz-11 had 6 growth-promoting characteristics, including nitrogen fixation, inorganic phosphorus solubilization, organic phosphorus solubilization, siderophore production, IAA production and ACC deaminase production, and the test tube identification results showed that it could effectively promote the growth and development of rice seedlings. The seedlings inoculated with strain Sz-11 increased by 36.08% and 22.70% in plant height and root length, respectively. Meanwhile, strain Sz-11 showed good antagonistic activity against various plant pathogenic bacteria, with significant and stable antagonistic effects against Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xooc). It was tentatively identified as Streptomyces zaomyceticus by observations, and experiments combined with sequencing analysis.[Conclusion]The number and distribution of dominant actinomycetes in waxberry orchard soil are influenced by season and altitude, and the proportion of growth-promoting strains among culturable actinomycetes is high. S. zaomyceticus has good disease prevention and growth-promoting function, which is expected to be developed into biofertilizer and biocontrol agent for rice production.