| The bacterial wilt,a worldwide soil-borned desease,is threating the production of tomato in China.While traditional methods to control the disease have drawbacks of one kind or another,biological control as an environmentally friendly and sustainable discipline emerged.Therefore,we need to breeding superior strains to make them more suitable for production use.This paper presents the mutation to SQR-T3,screening and identification of two superior mutant strains and some studies to them.The main results of this work were as following:(1)The mutagen dose and experimental conditions of UV and NaNO2 are definited in this experiment:a.UV irradiation 180s,wavelength of 260nm,power 15W,vertical distance 30cm;b.Suspending in 0.1mol/L NaNO2 solution for 12min.(2)After several compound mutagenesis and three rounds of screening,five strains are obtained:T-4,T-11,T-32,T-39 and T-43.Compared to the original strain,growth rate and inhibitory effect of them were both increased,the antibacterial circle increased by 24.I%,14.8%,22.2%,24.1%and 20.4%,and growth rate increased by 3.43%,9.38%,8.66%,11.89%and 10.30%.In the stability test,T-4,T-11 and T-43 were lost their advantages on the antibacterial activity,and therefore the T-32 and T-39 are the selected mutants for the latter experiment.(3)Compared with SQR-T3,T-32 and T-39 did not changes in their physiological and biochemical characteristics,sensitivity to antibiotics and 16s rDNA sequences.(4)Experimental study on colonization showed that three strains could colonize in tomato rhizosphere,and mutant T-39 given colonization density of 1.32 times the original strain SQR-T3,and up to 1.559 × 106 in 30 days after transplanting.(5)The three strains can effectively promote growth and improve the yield of tomato plants,especially in combination with the use of organic fertilizer.Compared with CK,tomato inoculated SQR-T3,T-32 and T-39,respectively,yield increased by 31.14%,34.52%and 49.74%;inoculation SQR-T3,T-32 and T-39 with organic fertilizer mixed were increased by 29.97%?44.58%and 50.51%than OF1.(6)Compared with the chemical fertilizer,organic can effectively reduce the incidence of tomato bacterial wilt,the disease severity index decreased by 0.89,control effects by 24.7%;SQR-T3,T-32 and T-39 with chemical fertilizers decreased their disease index by 1.00,1.06 and 1.19,control effects by 27.7%,29.4%and 33%;with organic fertilizer,the control effects reached 62.6%,65.4%and 70.0%;and compared with the original strain,the mutant T-39 had more significant prophylactic effect.(7)Test for bacteria SQR-T3,T-32 and T-39 shows the following conclusions:SQR-T3,T-32 and T-39 can secrete cellulase,?-1,3-glucanase and protease,and mutant T-39 has significantly improved as compared with CK on protease production capacity;synthetic genes of a variety of antagonistic substances,including Iturin,Bacillomycin,Subtilisin QK,Fengycin and Sufactin can be detected in the three biocontrol bacteria;all of them have the capable of producing lipopeptide active antagonists,and T-39 had the best performance.(8)The strains SQR-T3,T-32 and T-39 could get the maximum growth under conditions as following,the temperature of 30-37?,volume of 50 mL/250 mL,initial pH of 7.0,glucose as carbon source,and peptone as nitrogen source.In order to improve their production of antagonist material,the initial pH of 7.0,temperature of 30?,volume of 50 mL/250 mL,inoculum of 1%in Landy medium is the best choice. |
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