| Nowadays,biocontrol bacteria are widely used in agriculture.Pseudomonas fluores cens CPF10,a kind of Pseudonmonas fluorescens,is the mostly reported biocontrol stra in in pseudomonas genus.CPF10 is effective in the treatment and prevention of some soil-borne diseases(e.g.wilt disease and damping-off disease)in watermelon、cucumber and so on.With the continuous development of soil microbial community analysis technology,biocontrol bacteria influence on soil microbial community studies have drawn the attention of the people.Based on our previous studies,CPF10 might have impact on soil microbial community and some kind of soil microbial were dramatically changed.It is still unknown for us what roles of these bacteria have played in soils and how these strains affect the growth of plants.Thus,to understand the mechanism of biocontrol strains or find other functional flora,it is important to investigate these ba cteria.454 pyrosequencing was applied to analyze watermelon rhizosphere soil microbial after CPF10 treated.We Three dramatically changed strains were found.U36 is dramatic increase and U12、U40 are dramatic decrease.This study based on the functions and characteristics of the three strains to conduct a comprehensive analysis.The three strains were identified as Sporosarcina koreensis U12,Bacillus tequilens is U36,and Aeromonas media U40 by means of morphological,physiological and biochemical and molecular identification.The resistance research indicated that U36 showed good resistances to temperature,pH and salinity compared with U12 and U40.It can survive in the conditions of 55 ℃ and 10%salt concentration;But U12 and U40 at temperatures of up to 50℃ or in salt concentration of 10%and 5%respectively can not growth.The inhibition rate of U36 in the pH 4 and 9 conditions only have 22.8%and 22.8%.The inhibition rate reached 62.8%and 62.8%of U12 and U40 inhibition rate reached 51.8%and 19.0%.Besides,in the resistance research of agricultural fungicide,all three strains have no resistance to Bordeaux mixture,Kresoxim-methyl and Dimethachlon.For Kanamycinum Carbendazim and Hymexazol oxazole cycloheximide,U12、U36 and U40 could survive under a prescribed concentration.The interactions of three strains and microbial were also studied.U36 could not only against some of the common plant pathogenic,but also have certain antagonistic effect on indigenous microorganisms.And the growth of U36 was not affected by the indigenous bacteria.However,both U12 and U40 had no antagonism to pathogenic f ungi and indigenous microorganisms and the growth of the two strains were easily inhibited by indigenous bacteria.In a conclusion,U36 have stronger competitive ability.While U12 and U40 had relatively poor stability,which were vulnerable inhibited by other microbial.Besides,the effects of the isolated three strains on plant budding,growth and resistance were also studied.The budding experiment indicated that there was no significant difference between U12-treated group and the control group on root length(P>0.05).But the plant fresh weight and stem length were 15.9%and 20.6%inhibited by U12,respectively.In U36-treated group,stem length and plant weight showed no significant differences,but the root length was 41.5%promoted.There were not any significant differences between U40-treated group and the control group.Moreover,germination rates of both pepper and watennelon seeds were not affected by all three strains.In the experiment of pepper growth,both U36 and U40 showed promotion effects on pepper growth on 40th day.While U12 was the opposite.In contrast with the sterile soil,peppers which grew in usual soil were significantly affected by U12 and U36.Thus we concluded that U12 and U36 might directly affected the soil microbial and influenced the growth of plants indirectly.While U40 showed direct impact on plant growth.In the experiment of plant resistance,only U36 improved the water retention and the growth of plant under drought condition and consequently the drought resistance of plants was improved.Under salt stress conditions,plants may grow in U36-treated group and its salt resistance index were improved.However,the index was decreased when the plant treated by U12.U40 showed no significant impact on the salt resistance index of the plant.In a conclusion,U36 and U40 had a promotion effects on seeds gennination,plants growth and stress resistance,while U12 showed inhibition for the plant growth.By investigate the promoting mechanism of U36 and U40,production of sideroph ore,IAA,acetoin,and ACCD,nitrogen fixation and phosphate-solubilizing were discovered.U12 only produced small amounts of IAA and acetoin.All of these features may be the explanations of why U36 and U40 promoted and protected the growth of plants.As a conclusion,Pseudonmonas fluo,rescens CPF10 not only can product antibiotics to inhibit pathogen,but also promoted the growth of useful microbiological population,inhibited harmflul bacteria and finally to improve the soil environment.So we can know that Pseudonmonas.fluorescent CPF10 on soil micro ecological regulation is also an important part of the mechanism of bio-control.Importantly,U36,which was isolated from the soils,showed great growth promoting effects and was well tolerated.U36 may be used as a potential biological fertilizer in further studies.Nowadays most studies focused on the microbial communities,only a few studied the specific changed strains.So the understanding of the problem stay at the group level As we all know,these dramatic changed strains in soils may play special functions in soils,From the individual level of severe changes flora to research they interacted with the microorganisms and plants in soils for clear about the Pseudomonas fluore scent CPF 10 role in soil and provide ecological base for the Pseudonmonas fluorescent CPF 10 biological control mechanism. |
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