| Fresh corn is an important commercial crop in China.For the presence of diseases and pests,and the nutrition need during the development,large amount of pesticides and fertilizers are used in fresh corn plantation.Abuse of fertilizers and pesticides has negative impact on the food safety of fresh corn and the sustainable development of industrialization.In this study,the endophyte bacteria from the roots of fresh corn were isolated,and their functions of nitrogen fixation,phosphate solubilizing,potassium solubilizing,potential growth promoting and the antagonistic activity were eveluated.Some of those strains were used to test their influence on the germination,growth and agronomic traits of the sweet corn in field.The purpose of this study aims to select useful bacterial strains to reduce the application of chemical fertilizers and insectcides in the production of sweet corn,and improve the food safety of sweet corn.The fresh roots of sweet corns and waxy corns planted in breeding bases of Zhuhai Modern Agricultural Development Center(Dongken,Xiangzhou District of Zhuhai Ctiy,Pingsha Town of Zhuhai City,and Xinhui District of Jiangmen City)were used to screen the endophyte bacteria.By means of selective culture and dilution-plate method,those with the ability of phosphorus and potassium solubilizing,nitrogen fixation,IAA secretion were selected.The quantitative determination of the ammonia secretion,phosphorus and potassium solublizing were tested with indol blue spectrophotometric method,Mo-Sb colorimetric method and atomic absorption specrtoscopy.Confrontation experiment was performed to test the antagonistic activity of the isolated strains to fungal pathogens F.graminearum and F.verticillioides.In order to identify the isolated microbes,16 S rDNA,gyrB and hsp60 sequences of these strians were cloned and analyzed,along with a series of physiological biochemistry experiments.According to theie ability of phosphorus and potassium solublizing,nitrogen fixation and IAA production,several strains were selected to study thier effects on seed germination and growth promotion of the sweet corns.The main results were as follows:1.There were 266 strains of bacteria were isolated from the fresh corn roots with NA medium culture and 186 strains with ability of nitrogen fixation in Ashby nitrogen-free medium were further isolated.From the 186 strains,83 strains showed weak growth ability,63 moderate ability,40 high ability and 12 of them could produce hydrolytic circle on the plate.Specifically,Enterobacter cloacae P1-6 showed the highest level of nitrogen fixation and the ammonia secreted into the medium reached 2.41 ?g/mL.2.103 strains of bacteria with middle and high level of nitrogen fixation were used as experimental materials to test their ability of dissolving both phosphorus and potassium.The 35 strains from them were screened for their phosphorous solublizing,potassium solublizing and IAA secretion.The results showed that Enterobacter cloacae P1-6 had the best effect of dissolving inorganic phosphorus,and Bacillus altitudinis S-3-8 had the best effect of dissolving organic phosphorus.Bacillus megaterium P3-2 and Enterobacter cloacae P1-7 were found high level of dissolving patassium,and the Enterobacter cloacae S-2-14 was the second one with high level of dissolving patassium.The IAA secretion of Enterobacter cloacae S-2-12 was the highest(334.46±8.80 ?g/mL),and the IAA secretion of other strains of Enterobacter was between 200 ?g/mL and 300 ?g/mL,significantly higher than the control.3.Fusari?m graminearum and Fusarium verticillioides were chosen as indicator strain to test the antagonistic activity from the 35 bacterial strains isolated.The results showed that 12 bacteria of them had antagonistic activity to these fungus pathogens,and Bacillus amyloliquefaciens P4-2,S1-8 and S4-1 were found with the strongest antagonistic effect.4.The sequences of 16 S rDNA?gyrB and hsp60 of these strians were cloned,sequenced,and analyzed with Blast software in NCBI data bank.The phylogenetic trees of these strains based on the Blast data were constructed by using MEGA5.1 software.The results indicated that the strains P1-7,P1-6,S-2-2,S-2-12,S-2-8,S-2-11,S1-14 and S-2-14 belonged to Enterobacte cloacaer;CHI-1-2,P2-7,P2-13 and BC25-1-11 were Bacillus subtilis;I736-1,S-1-1,S4-1,S1-8,P4-2,P2-6,CHI-1-1,P1-1 and S-1-8 were Bacillus amyloliquefaciens;S-1-2,S-3-7,P4-7 and S-3-8 were Bacillus altitudinis;I736-3 and P3-4 were Bacillus thuringiensis;P1-5,P2-5,P3-2,I720-1 and P2-4 were Bacillus megatherium;S4-12,S1-15 were Bacillus asahhi.5.According to the classification of strains and their ability to produce IAA,four strains Enterobacter cloacae P1-6,Bacillus amyloliquefaciens CHI-1-1,S1-8 and Bacillus megaterium I720-1 were chosen to evaluate their effects on the germination of sweet corn 'Zhuyutian No.1',the results showed that germination rate of the treatments were lower than the control and the seeds treated by the strains with the highest IAA secretion showed the lowest germination rate.The treatments had significant effects on sweet corn biomass,and growth of roots were promoted significantly by strains S1-8,CHI-1-1 and 1720-1.Growth of stems were promoted significantly by strains P1-6 and CHI-1-1,and root fresh weight of seedlings treated by CHI-1-1 was significantly higher than that of the control and other treatments.6.According to the ability of solubilizing phosphorus,solubilizing potassium and IAA production,Enterobacter cloacae P1-6,P1-7,S-2-2 and Bacillus altitudinis P4-7 were selected to perform seed and field experiment of the corns for comparing their influence on seed germination,seedling growth,productivity and sweetness of sweet corn 'Zhuyutian No.1'.The results showed that only the strain P1-7 could significantly improve the sweetness of sweet corn 'Zhuyutian No.1',while it had not significant influence on other biological traits.7.Acccording to field experiment,Enterobacter cloacae strain P1-7 was selected to observe its growth promotion and quality on flowering cabbage in pot culture.The results showed that strain P1-7 increased the sweetness of the flowering cabbage,and also increased the vitamin C content of the flowering cabbage. |
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