Soil Microbial Diversity Analysis In Cotton Continuous Fields Under Continuous And Rotation Cropping Systems And Screening Of Plant-growth Promoting Rhizobacteria Strains

Research on soil microbial diversity in cotton under continuous and rotation cropping systems have been done through the biotechnology method and culture method, the results show that the continuous cropping obstacles of the bio-factors, continuous and rotation cropping present and trend. The PGPR strains which have prevent growth-promoting effects have been used to improve the ecological condition in the cotton fields, to study the how to deal with continuous cropping obstacles, and improve the cotton growing structure of cotton strains, provide a scientific basis and technical to support cotton industry developing healthy, sustainably and effectively.The results showed: the continuously cropping of cotton will cause the decrease of the cultivable microorganism number, compare to cropping less than 5a continuously, 6-8a, 9-12a and more than 13a of continuously cropping will cause the decrease of the soil microbe by 40.2%, 46.7%, 52.4%, the structure of the soil microbe translated from a rich nutrition bacteria type to the low nutrition fungi type gradually after 5a, the rate of B/F have decreased, pathogenic bacteria have accumulated.With the increasing of the years of continuously cropping, the number of ammonification bacteria, nitrifying bacteria, free-living nitrogen fixing bacteria in the soil have decreased, meanwhile the number of denitrifying bacteria have increased. Respiratory intensity, cellulolytic activity have decreased in continuously cropping field. Through the rotational cropping,the number of the soil microbe has increased obviously, the rate of B/F and A/F, the number of nitrogen-fixing bacteria and microbial activity have increased.A simple and efficient DNA extraction of the total microbial cotton method has been establishment-modified CTAB-SDS method. This method of extract DNA are integrity and also have higher rate, 24.20μg/g dry soil. The A260/A280 and A260/A230 after the purifying are 1.80 and 1.70, purification Recovery rate are 70.1%, it is totally fit for the next pcr analyzing, It provides the foundation for the study of the soil microbial diversity without culturing.The changes of bio-diversity in continuously and rotational cropping soil have been compared through the ARDRA and DGGE, it shows that the continuously cropping lower the number of the bacteria, diversity index, richness index and uniform index, the structure of the bacteria begin to have complicate changes after continuously cropping. 13a of continuously cropping was similar to cropping less than 5a continuously only 45 percent, There have obvious differences in the bio-structure of continuously cropping and rotational cropping, the bio-diversity has increased, and especially the tomato and melilotoides have great effects on improve the bacteria diversity in the continuously cropping field.The number of superiority soil bacteria have changed. One kinds of uncultured bacteria disappeared or weaked. Two kinds of uncultured bacteria be enriched. A number of nonsuperi- ority soil bacteria has been strengthened to rotational cropping fields.Screen out activity strains of CRB115 from rhizosphere with high antagonistic to Fusarium oxysporium f.sp. vasinfectum(Atk) Snyder et Hansen, Verticillium dahliae Kleb, Rhizoctonia solani kuhn. A pot experiment results showed it have played roles in preventing the disease, accelerating germination and increasing living weight after inoculation of the strains. Morphological identification combination with 16S rDNA sequence analysis identified as bacillus subtilis.