Screening And Medium Optimization Of PGPR From Tomato Rhizosphere

Tomato is an important cash crop,and with the cultivated area is continuously extending,continuous cropping result in decline of fertility,aggravation of soil-borne diseases,accumulation of self-toxiciting,which affecting the sustainable production of tomato.Plant Growth-promoting Rhizobacteria（PGPR）can produces plant growth regulators,improve or provide soil fertility,inhibit soil-borne diseases,induce system resistance and tolerance,and degrade autotoxicity.In the agricultural production has broad prospects.In this study,25 strains of bacteria selected from tomato rhizosphere soil were provided for the experiments,then we identified these bacteria,and tested the antagonism to Botrytis cinerea of them.The results showed that its capacities of producing IAA,iron carrier,protease,release organic phosphorus,solubilizing inorganic phosphorus,and the pot experiments was used to verify the effect of PGPRs on the growth of tomato.Two strains of bacteria with capacity of growth-promoting were optimized on medium.The 16S rRNA gene sequence data of the strain was obtained and the phylogenetic tree was constructed.The identifying results showed that SH180 belongs to Bacillus safensis,SH159 belongs to Bacillus subtilis,JF20 and SH160 belong to Bacillus tequilensis,SH10 and SH69 belong to Alcaligenes faecalis,JF12,JF32,JF38 belong to Bacillus siamensis,JF9,JF33,SH162,SH164 belong to Bacillus stratosphericus,JF2,JF27,JF31,JF45,SH35,SH81,SH82,SH98,SH122,SH143,SH183,SH184 belong to Bacillus xiamenensis.We measured 25 strains of bacteria potential ability to promote plant growth.20 strains of bacteria on Botrytis cinerea had better resistance,which SH180,SH183,SH164,JF27 these strains had excellent antagonistic effect.JF2 and JF38 have some antagonistic effect on E.Coli.24 strains of bacteria have the ability to produce protease,SH183 fermentation broth in the protease activity as high as 347.61μg/mL.In this study,we found that SH10,JF32,SH69have superior capability of producing iron carrier,the siderophore units was 69.27%,65.03%,48.63%.SH160 can produce IAA and all of these bacteria lack of the ability of release organic phosphorus or solubilizing inorganic phosphorus.We measured these bacteria potential ability to promote tomato growth by pot experiments.In the first pot experiments,the tomato plant height of SH180,SH183,SH69,SH98,SH164 increased 29.73%,29.05%,23.61%,19.05%,14.29%compared with control group（CK）respectively,SH180 and SH183 reached an extremely significant difference;the ground diameter of SH180 increased 8.02%;the tomato root length of SH183,SH164,SH184,SH180 increased 25.31%,19.87%,14.81%,13.54%respectively.According to agricultural traits we selected 5 strains to conduct the second pot experiments,that were SH180,SH183,SH164,SH69 and SH98.In the second pot experiments,The plant height of SH183,SH180,SH164,SH69,SH98 increased 19.13%,17.13%,10.49%,12.45%,2.93%compared with CK respectively,the plant height of SH183 and SH180 reached an extremely significant difference or significant difference;the tomato root length increased 22.97%,34.14%,23.78%,16.91%,4.62%respectively,SH180 reached a significant difference;the ground diameter of SH164 and SH180 increased 12.09%,10.11%,they reached an extremely significant difference or significant difference respectively;The overground fresh weight of SH180,SH183,SH164,SH69,SH98 increased 52.46%,35.16%,35.63%,19.00%,0.28%compared with CK respectively,SH180 reached an extremely significant difference,SH183 and SH164reached significant difference;the overground dry weight of SH180,SH164,SH183 increased60.31%,55.56%,44.44%respectively,they reached an extremely significant difference or significant difference respectively;the root fresh weight of SH164,SH180,SH69,SH183increased 85.42%,71.88%,43.75%,36.46%,they reached an extremely significant difference or significant difference respectively;the root dry weight of SH180,SH183,SH164,SH69,SH98 increased 55.56%,55.56%,55.56%,38.89%,33.33%respectively,SH180,SH183,SH164 reached an extremely significant difference,SH69 and SH98 reached a significant difference.The two strains,SH180 and SH183,which were effective and stable in two experiments were selected,then optimized the medium for cultivating and tested by dilution coating method.The based medium was used as the bean sprouts for the addition of 3%sucrose,and the appropriate carbon source,nitrogen source and inorganic salt were selected by single factor experiment.The carbon source used in the single factor test was glucose,sucrose,lactose,corn flour and soluble starch.The nitrogen source used was tryptone,yeast extract,soybean meal,sodium nitrate,ammonium chloride and urea.The inorganic salt used was CaCO₃,MgSO₄·7H₂O,K₂HPO₄,KH₂PO₄,FeSO₄·7H₂O,CuSO_4.The optimal carbon sources for SH180 and SH183 were glucose and sucrose,respectively.The optimal nitrogen sources was soybean meal for SH180 and SH183.The best inorganic salts for SH180 and SH183 are Fe SO₄·7H₂O and KH₂PO₄,respectively.And then use the orthogonal test to determine the best medium formula.The best medium of SH180 was:4%glucose,2%soybean meal,0.003%FeSO₄·7H₂O.The best medium of SH183 was:4%sucrose,2%soybean powder,0.3%KH₂PO₄.