| Indole acetic acid(IAA)is a plant hormone that plays an important role in plant growth and development.It can effectively promote the growth and development of plant roots,stems,buds and enhance the synthesis of RNA.Bacillus has the characteristics of rapid reproduction,strong resistance to stress and favorable industrial production.Therefore,in this study,L-tryptophan-containing liquid medium was used to screen Bacillus with high IAA-producing ability.Two multi-functional strains were obtained by synthesizing their biological characteristics such as phosphorus-solubilizing and protein-lowering.Then the effects of the germination of Chinese cabbage seeds and the root development of Arabidopsis thaliana were studied by using the culture filter paper method.The plant growth promoting effect was further verified by the Chinese cabbage and corn pot experiment.The main results are as follows:(1)In this study,six strains producing IAA more than 30.78 mg·L-1 were obtained in liquid medium containing L-tryptophan,which was cultured at 30 C and 180 rpm for 24hours.They were W56,B24,YC1,YC2,YC3 and YC4.Among them,W56 strain had the highest IAA production capacity,reaching 48.04 mg·L-1,followed by B24 reaching 44.41mg·L-1.After 7 days of culture in Mengjinna liquid medium,the amount of water-soluble phosphorus in the culture solution was 14.51?91.28 mg·L-1.Using the skim milk powder medium and peptone water medium,6 strains were found to have reduced protein and ammonia production.Six strains were identified as Gram-positive bacteria(G+)by Gram staining and spore staining,and all had sporulation ability.According to the physiological and biochemical characteristics of the strain and 16S r DNA sequence analysis,W56,YC1,YC2,YC3 and YC4 were initially identified as Bacillus aryabhattai,and B24 was identified as Bacillus megaterium.(2)In the experiment of Chinese cabbage seed germination by using the culture dish filter paper method,strains B24 and W56 could improve the germination rate,bud length and stem diameter of Chinese cabbage seed.In the root development test of Arabidopsis thaliana,compared with CK,B24 solution with concentrations of 2.11×107cfu·m L-1,2.11×106cfu·m L-1,and 2.11×105 cfu·m L-1 increased the number of adventitious roots by60.34%?74.50%.The root length of Arabidopsis thaliana increased by 117.44%at the concentration of 2.11×105 cfu·m L-1.The adventitious roots of Arabidopsis thaliana increased by 23.26%?67.38%when the concentration of W56 was 5.56 x 106 cfu·m L-1,5.56 x 105cfu·m L-1 and 5.56 x 104 cfu·m L-1.The root length of Arabidopsis thaliana was increased by94.39%when the concentration of W56 was 5.56 x 105 cfu·m L-1.(3)In the potted cabbage experiment,the plant height and leaf number of Chinese cabbage increased by 50.73%,37.81%,28.95%and 29.61%,after 7 days of application of B24 and W56 bacteria.Compared with CK,the plant height,leaf length,leaf width,leaf number,root length,root dry weight and leaf dry weight of Chinese cabbage treated by strain B24 increased 51.68%,66.67%,62.71%,34.50%,54.01%,142.11%and 78.30%respectively after 14 days of inoculation.Compared with CK,Chinese cabbage treated by W56 strain increased by 40.32%,52.46%,53.22%,30.41%,47.00%,133.07%and 73.22%,respectively.(4)The growth of corn could be significantly promoted by both methods.Compared with CK,the stem and leaf dry weight and root dry weight ratio of corn plants increased by27.71%,92.24%,45.53%and 117.50%in the corn potting experiment.In the corn pot experiment of root-inoculation,the dry weight and root dry weight of stems and leaves of B24 and W56 strains increased by 111.90%,153.55%and 83.24%,119.79%.It is indicated that both microbial agents can significantly promote the growth of potted corn.Moreover,the method of irrigating roots has a stronger ability to promote corn plants.In summary,two strains of Bacillus strains,B24 and W56,were screened in this study.They had stable IAA production capacity and multiple growth promoting functions.It can promote the root growth of Arabidopsis thaliana and the seed germination and stem development of Chinese cabbage.In pot experiment,B24 and W56 showed strong growth promoting ability,significantly promoted the growth of roots,stems and leaves of pakchoi and maize,and were expected to be developed into biofertilizers,which had good application prospects in agricultural production. |
PDF Full Text Request