| Pepper is an important advantageous industry in Guizhou province,and as environment-friendly biofertilizers,microbial agents prepared with plant growth-promoting rhizobacteria(PGPR)play an important role in promoting plant growth and improving crop yield.Facility agriculture has gradually become an important part of modern agriculture in China and has great significance for chili seedlings.In this study,four PGPR strains with obvious growth-promoting effects on pepper,Pseudomonas putida HGD3,Bacillus velezensis HP9,Burkholderia pyrrocinia P10,and Bacillus flexus HGD12 was used.In order to build multifunctional growth promoting microbial agents,the mode of co-fermentation,the growth-promoting characteristics of different combinations of strains,the effect of co-fermentation solution on seed germination of chili were analyzed.In order to develop the biological seedling substrate and explore the mechanism of growth-promoting effect of PGPR on chili seedlings,different proportion of co-fermentation solution were mixed with seedling substrate,and the effects on chili seedlings were analyzed.The main research results are as follows:(1)Using two co-fermentation modes of simultaneous fermentation and delayed fermentation,after the compatibility analysis of different strains and the growth amount test of strain combination co-fermentation,HP9 was found to be slightly antagonistic to HGD12 strain.And combined with the comparison of IAA and siderophore secreting capacity of different strain combinations under two fermentation modes,P10+HGD12,HP9+P10,HP9+P10+HGD12 strain combinations were preliminary screened.The co-fermentation solution,bacterial suspension and supernatant of these three combinations were soaked with chili seeds,which showed that the co-fermentation solution and supernatant had more significant germination-promoting effect on seeds,and co-fermentation solution was selected as the type of liquid multifunctional growth-promoting bacterial agent.(2)After the simultaneous fermentation solution and delayed fermentation solution of three combinations of strains P10+HGD12,HP9+P10 and HP9+P10+HGD12 were mixed into the seedling substrate,the experiment of promoting pepper seed germination was conducted.It was found that the seed germination rate,strong seedling index,plant height,fresh weight and leaf numbers of P10+HGD12 simultaneous fermentation solution treated pepper were the highest,so this combination liquid was selected as the compositon of multifunctional growth promoting microbial agent.The biological seedling substrate prepared with 5%-25% bacterial solution for cavity tray seedling,it showed that 15%(v/w)bacterial solution treatment had the highest germination rate,germination index,germination potential and survival rate,in which was increased by 32.99%,200.00% and 22.67%,respectively.In addition,the plant height,root length,dry weight,leaf number,leaf area and strong seedling index of germinating seedlings was increased by 29.17%,32.11%,94.44% 22.29%,49.45%,and 75.00%,respectively,thus determining a 15% addition rate of bacterial solution to the biological seedling substrate.(3)The mechanism of growth-promoting of biological seedling substrate composed of P10+HGD12 was studied.It showed that the promotion of seed germination and seedling growth by the co-fermentation solution of the two strains was significantly better than that of the two single strain groups.Both single and mixed strains could promote the increasing of organic matter,available nitrogen and available phosphorus content of the substrate,however the co-fermentation solution of the two strains significantly decreased the content of available potassium compared with the single strain.The analysis of the bacterial diversity of the substrate showed that the relative abundance of Proteobacteria of the substrate in the P10+HGD12 treated group decreased compared with the CK group,and the abundance of Bacteroidota,Firmicutes,Actinobacteriota and Patescibacteria increased compared with CK and P10 treatment;the abundance of Bacteroidota,Firmicutes and Halobacterota increased compared with HGD12 treatment.The results on fungal diversity showed that the abundance of Ascomycota and Chytridiomycota in P10+HGD12 treatment decreased compared to CK and single agent,the abundance of Mucoromycota decreased compared to CK,the abundance of Basidiomycota decreased significantly compared to HGD12 treatment,and the abundance of Rozellomycota increased compared to CK.Overall,the multifunctional growth promoting microbial agent increased the relative abundance of beneficial microorganisms in the substrate,reduced the abundance of some possible pathogenic microorganisms,and had a certain effect on enhancing the nutrient conditions of the substrate and promoting seed germination.(4)After the biological seedling substrate was applied to floating seedling cultivation of peppers,various indicators of pepper seed germination and seedling growth significantly improved,the germination rate and seedling strength index were significantly increased by 62.07% and 61.84%compared to CK,respectively,and there was more developed root system and higher growth volum. |
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