Isolation, Identification And Characteristics Of Endophytic Bacteria From Alfalfa

There are many kinds of endophytic bacteria living in various organs and tissues of many kinds of plants. These endophytic bacteria can help the plants resist diseases through secreting different kinds of helpful metabolites, competing ecological niche and nutrient substances with the pathogenic fungus, inducing systemic resistance and many other different mechanisms. Alfalfa(Medicago sativa L.) is an old perennial leguminous pasture. It contains rich nutrient, such as different kinds of essential amino acids, rare amino acids and digestible proteins. It also has strong tolerance to barren soils and drought. In this study, endophytic bacteria of the alfalfa plants were used as experimental materials, and their biocontrol characteristics and effects had been evaluated. The results were as follows:1. Isolating, screening and identification of endophytic bacteria60 strains of endophytic bacteria were isolated from the alfalfa plants and 6 strains which showed antagonism against Fusarium oxysporum in dual culture assay were selected. According to 16 S r DNA sequencing analysis, morphology, physiological and biochemical characteristics, the isolated strains were identified as: Y1 and Y5 were Bacillus subtilis, G43 was Pseudomonas chlororaphis, Y22 was Enterobacter amnigenus, G62 was Pseudomonas argentinensis, G68 was Enterobacter hormaechei.2. Effects of biocontrol by the endophytic bacteriaIn dual culture assay, 6 strains showed antagonism against different kinds of plant pathogenic fungi to varying degrees. The fermentation broth of the 6 strains could inhibit the growth of mycelia and spores of F. oxysporum, make the mycelia break and produce deformities, and reduce the numbers of the spores. In pot experiments, the disease conditions of the alfalfa plants that were treated with the 6 strains were alleviated to varying degrees. The relative control effect of Y22 was the highest and reached to 53.97%.3. Characteristics of the endophytic bacteriaThe abilities to synthesize siderophore and produce HCN, the chitinase activity and the cellulase activity of the 6 strains were evaluated. The 6 strains could all synthesize siderophore and produce chitinase. The ability to synthesize siderophore of Y22 was the highest, and the value was 0.521. The chitinase activity of G62 was the highest, and the value was 0.355 IU/m L. All the strains could produce HCN except G62, and the ability of G43 to produce HCN was the strongest. Y1 and Y5 could produce cellulase, and the values of the cellulose activity were 0.486 IU/m L and 0.360 IU/m L, respectively.