Study On The Preparation Of PGPR Multiple Bacterial Agents And The Field-promoting Effect On Chilli

Chilli is the main crop in Guizhou province,which has the highest planting area in China.Although the excessive application of chemical fertilizer could increase the crop yields,it also leads to agricultural pollution.Using microbial fertilizer replace of chemical fertilizer partially should reduce environmental pollution.Plant growth promoting rhizobacteria?PGPR?is a class of bacteria isolated from plant rhizosphere soil,which can promote plant growth and increase stress resistance.Microbial fertilizers,insisted of PGPR,can promote plant growth through those functions,such as nitrogen fixation,phosphorus dissolution,potassium hydrolysis and secretion of plant hormones,etc..In this paper,four PGPR strains,named as Pseudomonas putida HGD3,Bacillus velezensis HP9,Burkholderia cepacian P10 and Bacillus flexus HGD12,isolated from tea rhizosphere,were used as the research materials.The fermentation system of the multiple bacterial agents was constructed,and chill's inoculation experiment was carried out under field conditions,in order to explore the plant-growth promoting effect and mechanism of this multiple bacteria agents.The main findings were as follows:Using different combinations of multiple bacteria,pot experiments of chilli seedlings were carried out and it found that the culture of four strains had significant effect on the growth of chilli,So the multiple bacterial agents was consisted of four strains The inoculation sequences of the multiple bacteria fermentation was determined according to the growth curves of the four strains,that is,first inoculated with P10,then HP9 five hours'later,and another two hours's interval inoculation with HGD3 and HGD12 together.By the optimization of single factor and orthogonal experiment,the medium formula was constructed,that is,sucrose 18.65 g,yeast extract 12.53 g,Na₂HPO₄4.0 g,Na H₂PO₄2.0 g,Mg SO₄0.5 g,Ca Cl₂0.2 g,1000 m L distilled water.And analyzing single factor experiment combined with response surface method,the optimum fermentation conditions was obtained,which is,temperature 29.7°C,culture medium p H 7.045,inoculation rate 3.19%,medium volume 50 m L/250 m L.The growth-promoting effects of the two multiple bacterial agents were evaluated through pot experiments,the results showed that the multiple bacterial fermentation agents significantly promoted the increase of chilli's plant height,root weight,fresh weight and chlorophyll content,and these indexes were increased by 8.01%,50.22%,43.66%and 6.94%compared with the single-bacterial agent mixture group,respectively.The field growth promotion study of chilli was carried out by using multiple bacterial agents.Three treated groups,including,100%chemical fertilizer+PGPR multiple bacterial agents,80%chemical fertilizer+PGPR multiple bacterial agents,and 100%chemical fertilizer group as control.Effects of PGPR multiple bacterial agents were comprehensively evaluated on the growth,development and fruit of two varieties of chill,and community structure of rhizosphere soil microorganisms.The result showed that,comparing to 100%chemical fertilizer control group,the plant height and stem diameter of the two varieties of chill,named as Yan Jiao-425 and Zun La-9,inoculated with PGPR agents,increased in different degrees during fruit-setting and fruit-bearing stages.At Yan Jiao-425,the fruit numbers per plant increased 32.17%and 52.55%,the yield per plant increased 34.14%and 38.76%,respectively.At another variety Zun La-9,the fruit numbers per plant increased 14.82%and 7.24%,the yield per plant increased 28.74%and22.10%,respectively;and weight of per fruit obviously increased,too.Therefore,the application of PGPR multiple bacteria significantly promoted the growth and yield of chilli,the yield of Yan Jiao-425 was significantly increased even though reduced 20%chemical fertilizer.Dynamic monitoring results of microbial quantity in rhizosphere soil showed that,after treatment with PGPR multiple agents,significant increase were existed in the numbers of microorganism and bacteria and obvious decrease in the the numbers of fungi the numbers of actinomycetes in fruit-bearing period increased significantly.while functional bacteria numbers,including nitrogen-fixing bacteria,phosphate-solubilizing bacteria,potassium-solubilizing bacteria,increased in general with different degrees.Bacterial diversity analysis showed that the inoculation of PGPR multiple agents improved the species diversity and community structure of rhizosphere bacteria of Zun La-9,increased the relative abundance of Bacillales,Burkholderiales,Sphingobacteriales,etc..Pearson index showed that chilli yield and single fruit weight were positively correlated with bacterial diversity and abundance in rhizosphere soil.In addition,the PGPR multiple bacterial granules was preliminary prepared.Using the sodium alginate and polyving akohol?PVA?as embedding material,the influence of different concentration and proportion of embedding agent on the basic index of granular bacterial agents was investigated,and the composition was determined to be 2%PVA-3%SA-4%Si O2-0.3%Ca CO₃.In this condition,the granular bacterial agents had good sphericity and mechanical strength,the embedding rate was the highest,and the continuous releasing ability of living bacteria was stable.Another dosage form,solid bacterial agents were prepared using peat as the main materials,the formula was peat 250 g plus 1%sodium alginate solution 73 m L,the storage stability of this solid agent was better under this condition.These results established a foundation for further studying microbial fertilizer.