阅读说明：本技术 一种利用活体生测体系筛选烟草青枯病生防菌的方法 (Method for screening biocontrol bacteria for tobacco bacterial wilt by using living biological test system ) 是由 卢灿华 晋艳 盖晓彤 米梦鸽 马俊红 姜宁 高朝阳 莫献化 刘春明 雷丽萍 夏振 于 2020-12-08 设计创作，主要内容包括：本发明公开了一种苗期烟草青枯病生防菌的筛选方法,包括烟苗培育、生测初筛和复筛及温室盆栽等步骤。本发明采用漂浮育苗方式培育烟草青枯病感病烟苗,将烟苗分为试验组和对照组,分别对试验组和对照组接种候选生防菌和LB液体培养基,1～2d后挑战接种烟草青枯菌,将育苗盘置于28～30℃恒温温室培育,调查筛选具有控病能力的生防菌；再次用烟苗生测法验证防效,复筛时每个处理组和对照组的烟苗为6～16株,筛选具有明显控病能力的生防菌；最后在温室大棚内进行盆栽试验,评价生防菌对烟草青枯病的防治效果。运用该方法已获得多株非拮抗作用的烟草青枯病生防菌。(The invention discloses a screening method of biocontrol bacteria for tobacco bacterial wilt in seedling stage, which comprises the steps of tobacco seedling cultivation, primary screening and secondary screening for bioassay, greenhouse potting and the like. The method comprises the steps of cultivating tobacco seedling with a floating seedling cultivation mode, dividing the tobacco seedling into a test group and a control group, respectively inoculating candidate biocontrol bacteria and LB liquid culture media to the test group and the control group, challenging and inoculating tobacco ralstonia solanacearum after 1-2 days, placing a seedling tray in a constant-temperature greenhouse at 28-30 ℃ for cultivation, and investigating and screening the biocontrol bacteria with disease control capacity; verifying the control effect by using a tobacco seedling bioassay method again, wherein 6-16 tobacco seedlings are selected for each treatment group and each control group during rescreening, and biocontrol bacteria with obvious disease control capability are screened; and finally, carrying out a pot experiment in a greenhouse to evaluate the control effect of the biocontrol bacteria on the tobacco bacterial wilt. A plurality of strains of tobacco bacterial wilt biocontrol bacteria with non-antagonistic action are obtained by applying the method.)

1. A method for screening biocontrol bacteria for tobacco bacterial wilt by using a living biological test system is characterized by comprising the following steps:

step S1: the primary screening is carried out in the raw test,

(1) taking a diseased tobacco variety Honghuadajinyuan as a test object, carrying out floating seedling culture to cultivate tobacco seedlings to 4-5 leaf stages, and dividing the test object into a test group and a control group, wherein each group comprises 2 tobacco seedlings;

(2) firstly, injuring the root of a tobacco seedling, inoculating 1mL of candidate biocontrol bacteria for 48h in a test group, taking the tobacco seedling inoculated with an LB liquid culture medium as a control group, placing a floating disc in a constant-temperature artificial climate chamber for culturing for 1-2 d, challenging the test group and the control group to inoculate ralstonia solanacearum, and continuously culturing in the constant-temperature artificial climate chamber;

(3) observing the disease incidence of the test group and the control group, recording the disease incidence of the tobacco plants of the test group when the disease incidence of the control group is more than 80%, and screening biocontrol bacteria with disease control capability;

step S2: the raw test is carried out again to sieve,

(1) secondary screening of the biocontrol bacteria obtained by primary screening of the biological assay is carried out, 8-16 tobacco seedlings are respectively treated by a treatment group and a control group during secondary screening, and the method for root injury of the tobacco seedlings, inoculation of the biocontrol bacteria and inoculation of ralstonia solanacearum is the same as the step S1;

(2) disease grades of tobacco seedlings treated in each step are investigated 10d and 20d after the ralstonia solanacearum is inoculated, disease indexes are calculated, and biocontrol bacteria with control effects are screened and used for verifying control effects of greenhouse potting plants;

step S3: the greenhouse is verified by the verification method,

(1) the greenhouse control effect evaluation of the biocontrol bacteria is carried out in a greenhouse with the temperature of 28-30 ℃, a ralstonia solanacearum treatment group and a control group are set in the test, and the process is repeated for 3 times, and 10 tobacco plants are repeated for each time;

(2) culturing biocontrol bacteria with LB culture solution at 225r/min at 30 deg.C for 48 hr; culturing pathogenic ralstonia solanacearum with CG liquid culture medium, and shaking at 30 deg.C at 225r/min for 24 hr;

(3) uniformly mixing the red soil and the organic matter according to a ratio of 3:1, transplanting tobacco seedlings, namely tobacco seedlings with secondary leaf cutting, culturing for about 50d, diluting 250mL of biocontrol bacterium fermentation liquor by 25 times after transplanting, irrigating roots of a test group, and treating a control group by using an equal volume of LB diluent; inoculating 100 times of dilution of tobacco ralstonia solanacearum to each tobacco strain challenge the next day; after inoculation, the disease index is investigated every 7 days, and 5 times of continuous investigation are carried out;

(4) counting according to the investigation result; and calculating the morbidity, disease index and prevention effect.

2. The method of claim 1, wherein: the specification of the floating plate is 8 multiplied by 14 and 9 multiplied by 18 hole floating plates.

3. The method of claim 1, wherein: the LB liquid medium comprises 1% tryptone, 0.5% yeast extract, 1% sodium chloride and 0.5% sucrose; the CG medium contained 0.1% acid hydrolyzed casein, 0.5% glucose, and 2% peptone.

4. The method of claim 1, wherein: the biocontrol bacteria and the ralstonia solanacearum are inoculated in sequence, namely, after wounds are formed on two sides of the root of the tobacco seedling by using a sterile blade, the root of the tobacco seedling is pretreated by using the biocontrol bacteria, and then the pathogenic bacteria are inoculated after 1-2 days, or the biocontrol bacteria and the pathogenic bacteria are simultaneously irrigated into the root of the tobacco seedling.

5. The method of claim 1, wherein: the inoculation amount of the ralstonia solanacearum in the steps S1 and S2 is 1.0mL multiplied by 10⁷～1.0mL×10⁹CFU/mL, the inoculation amount of biocontrol bacteria is 1.0mL multiplied by 10⁸～1.0mL×10⁹CFU/mL。

6. The method of claim 1, wherein: the inoculation amount of the ralstonia solanacearum in the step S3 is 50mL multiplied by 10⁷～50mL×10⁸CFU/mL, the inoculation amount of biocontrol bacteria is 200mL multiplied by 10⁷～200mL×10⁸CFU/mL。

7. The method of claim 1, wherein: the temperature of the constant-temperature artificial climate chamber is set to be 28-30 ℃.

8. The method according to any one of claims 1 to 7, wherein: the incidence is the total number of diseased plants/investigated plants x 100%.

9. The method according to any one of claims 1 to 7, wherein: the disease index is 100 multiplied by sigma (each stage of disease plant number multiplied by each stage of representative value)/total plant number multiplied by the highest stage representative value is investigated;

wherein, the disease degree of the tobacco plants is divided into 0, 1, 3, 5, 7 and 9 grades according to the disease grade.

10. The method according to any one of claims 1 to 7, wherein: the control effect is 100 x (disease index of a control group-disease index of a treatment group)/disease index of a control group.

Technical Field

The invention relates to the field of plant pathology, in particular to a method for screening biocontrol bacteria for tobacco bacterial wilt by using a living biological test system.

Background

Tobacco Bacterial Wilt (TBW) is one of the common plant bacterial diseases in tropical, subtropical and some temperate regions. The disease is commonly generated in Yangtze river basin and other big smoke areas in the south of China, wherein Yunnan, Guizhou, Sichuan, Chongqing, Fujian, Guangxi, Anhui and other provinces and cities are seriously damaged, often outbreak and epidemic, and cause destructive loss.

The method for preventing and treating the tobacco bacterial wilt mainly comprises the steps of utilizing disease-resistant varieties, chemical prevention and treatment, agricultural prevention and treatment, biological prevention and treatment and the like. The biological control is widely concerned by researchers at home and abroad due to the environmental safety, and is one of the ideal measures for sustainable green control.

At present, the biological control method for preventing and treating plant diseases is greatly developed and shows diversified development trends, and the biological control method becomes one of important measures for preventing and treating the diseases on part of crops. The screening method of biocontrol bacteria is a bottleneck in the field of biological control research, and most researchers use an in vitro plate method for primary screening, namely screening strains with bacteriostatic activity on pathogenic bacteria on a plate (Hanchang. the current research situation and development trend of biocontrol bacteria for plant diseases [ J ]. forest diseases and pests in China, 2015,34(01):33-37, 25.). For example, 8 kinds of registered biocontrol bacteria on tobacco in China mainly comprise bactericides such as pseudomonas fluorescens, bacillus amyloliquefaciens, paenibacillus polymyxa and bacillus subtilis, and most bactericides have the capacity of antagonizing ralstonia solanacearum. The method for obtaining potential biocontrol bacteria by antagonistic primary screening plays a great role in biological control of plant diseases, but the method also has the defects. The traditional screening method is not easy to screen biocontrol bacteria which can prevent diseases by non-antagonism, for example, many bacteria can control diseases by mechanisms such as competition, growth promotion, plant disease resistance induction and the like. In recent years, in vivo test systems have been introduced into screening of biocontrol bacteria against plant diseases, for example, screening of biocontrol bacteria and agents against cotton rhizoctonia solani, which have been screened by the in vivo test method for obtaining a plurality of strains (species) having a certain development value (in vitro test system for screening of biocontrol bacteria and agents against cotton rhizoctonia solani [ D ] in Hebei agriculture university, 2015.). At present, the application of a living body biological test method in the biological control bacteria screening of tobacco diseases is temporarily absent.

Disclosure of Invention

In order to solve the problems and the defects of the prior art, the invention provides a method for screening biocontrol bacteria for tobacco bacterial wilt by using a living biological test system.

In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:

a method for screening biocontrol bacteria for tobacco bacterial wilt by using a living biological test system is characterized by comprising the following steps:

step S1: the primary screening is carried out in the raw test,

(1) taking a diseased tobacco variety Honghuadajinyuan as a test object, carrying out floating seedling culture to cultivate tobacco seedlings to 4-5 leaf stages, and dividing the test object into a test group and a control group, wherein each group comprises 2 tobacco seedlings;

(2) firstly, injuring the root of a tobacco seedling, inoculating 1mL of candidate biocontrol bacteria for 48h in a test group, taking the tobacco seedling inoculated with LB culture solution as a control group, placing a floating disc in a constant-temperature artificial climate chamber for cultivation for 1-2 d, challenging the test group and the control group to inoculate ralstonia solanacearum, and continuing cultivation in the constant-temperature artificial climate chamber;

(3) observing the disease incidence of the test group and the control group, recording the disease incidence of the tobacco plants of the test group when the disease incidence of the control group is more than 80%, and screening biocontrol bacteria with disease control capability;

step S2: the raw test is carried out again to sieve,

(1) secondary screening of the biocontrol bacteria obtained by primary screening of the biological assay is carried out, 8-16 tobacco seedlings are respectively treated by a treatment group and a control group during secondary screening, and the method for root injury of the tobacco seedlings, inoculation of the biocontrol bacteria and inoculation of ralstonia solanacearum is the same as the step S1;

(2) disease grades of tobacco seedlings treated in each step are investigated 10d and 20d after the ralstonia solanacearum is inoculated, disease indexes are calculated, and biocontrol bacteria with control effects are screened and used for verifying control effects of greenhouse potting plants;

step S3: the greenhouse is verified by the verification method,

(1) the greenhouse control effect evaluation of the biocontrol bacteria is carried out in a greenhouse with the temperature of 28-30 ℃, a ralstonia solanacearum treatment group and a control group are set in the test, and the process is repeated for 3 times, and 10 tobacco plants are repeated for each time;

(2) shaking and culturing the biocontrol bacteria in an LB liquid culture medium at the temperature of 30 ℃ at 225r/min for 48 hours; shaking culture of pathogenic ralstonia solanacearum in CG liquid culture medium at 225r/min and 30 deg.C for 24 hr;

(3) uniformly mixing the red soil and the organic matter according to a ratio of 3:1, transplanting tobacco seedlings, namely tobacco seedlings with secondary leaf cutting, culturing for about 50d, diluting 250mL of biocontrol bacterium fermentation liquor by 25 times after transplanting, irrigating roots of a test group, and treating a control group by using an equal volume of LB diluent; challenge inoculation test group and treatment group by using tobacco ralstonia solanacearum on the next day; disease index was investigated every 7 days after inoculation, and 5 consecutive investigations were performed.

(4) Counting according to the investigation result; and calculating the morbidity, disease index and prevention and treatment effect (the prevention effect can be called for short).

Further, the specification of the floating plate is 8 × 14 and 9 × 18 hole floating plates.

Further, the LB liquid medium comprises 1% tryptone, 0.5% yeast extract, 1% sodium chloride and 0.5% sucrose; the CG medium contained 0.1% acid hydrolyzed casein, 0.5% glucose, and 2% peptone.

Further, the biocontrol bacteria and the ralstonia solanacearum are inoculated in sequence, namely, after wounds are formed on two sides of the root of the tobacco seedling by using a sterile blade, the root of the tobacco seedling is pretreated by using the biocontrol bacteria, and then the pathogenic bacteria are inoculated after 1-2 days, or the biocontrol bacteria and the pathogenic bacteria are simultaneously irrigated into the root of the tobacco seedling.

Further, theThe inoculation amount of the ralstonia solanacearum in the steps S1 and S2 is 1.0mL × 10⁷～1.0mL×10⁹CFU/mL, the inoculation amount of biocontrol bacteria is 1.0mL multiplied by 10⁸～1.0mL×10⁹CFU/mL。

Further, the inoculation amount of ralstonia solanacearum in step S3 was 50mL × 10⁷～50mL×10⁸CFU/mL, the inoculation amount of biocontrol bacteria is 200mL multiplied by 10⁷～200mL×10⁸CFU/mL。

Further, the temperature of the constant-temperature artificial climate chamber is set to be 28-30 ℃.

Further, in the bioassay rescreening, the incidence rate is ═ diseased plants/total number of investigated plants × 100%.

Further, in the bioassay rescreening, the disease index is 100 × ∑ (number of disease plants per grade × representative value per grade)/number of total investigated plants × highest representative value, wherein the disease degree of tobacco plants is classified into 0, 1, 3, 5, 7 and 9 grades according to disease grade.

Further, the biocontrol bacterium control effect is 100 x (disease index of a control group-disease index of a treatment group)/disease index of a control group.

The working principle is as follows:

the invention screens the biocontrol bacteria for the tobacco bacterial wilt by three steps of primary screening, secondary screening and greenhouse verification. Firstly, cultivating tobacco seedling with bacterial wilt disease by adopting a floating seedling cultivation mode, dividing the tobacco seedling into a test group and a control group, respectively inoculating candidate biocontrol bacteria and LB culture medium to the test group and the control group, challenging and inoculating tobacco ralstonia solanacearum after 1-2 days, putting a seedling cultivation disc in a constant temperature greenhouse at 28-30 ℃ for cultivation, and investigating and screening the biocontrol bacteria with disease control capability; verifying the control effect of the biocontrol bacteria obtained by primary screening of the biological test indoors by using a tobacco seedling biological test method, and screening the biocontrol bacteria with obvious disease control capability; and finally, performing greenhouse control effect evaluation on the biocontrol bacteria with better control effect in the secondary screening, and screening the biocontrol bacteria with stable control effect.

Compared with the prior art, the invention has the following beneficial effects:

(1) the conventional in-vitro flat plate antagonism method takes an indoor flat plate as a screening environment, has obvious difference with natural soil, adopts a living body bioassay method to artificially simulate disease conditions, is closer to natural disease conditions, and is more beneficial to screening biocontrol bacteria with application value in the field;

(2) the invention firstly screens the biocontrol bacteria with disease prevention and control capacity by a living body bioassay system, and then analyzes the disease prevention mechanism of the biocontrol bacteria, and the conventional technology screens the antagonistic bacteria by an in vitro flat plate antagonism method to detect the disease prevention capacity, so the invention can screen the biocontrol bacteria which have the functions of preventing and controlling diseases, such as antagonism, competition, promoting growth, inducing disease resistance, and the like;

(3) compared with the conventional nutrition bag transplanting, the tobacco seedling cultivation method adopting the floating seedling cultivation mode has the advantages of high tobacco seedling cultivation efficiency, small occupied space, simple, convenient and quick seedling cultivation and transplanting modes, high efficiency and large screening biocontrol bacteria flux.

Drawings

FIG. 1 is a flow chart of the present invention.

FIG. 2 is the structural explosion diagram of tobacco seedling root suspension culture method.

FIG. 3 is a side view of the tobacco seedling root suspension culture method.

Reference numerals in the drawings: 1-floating plate, 2-disposable culture dish, 3-thick plastic cloth.

Detailed Description

The following detailed description will be made with reference to specific embodiments and accompanying drawings, but the present invention is not limited to the following embodiments.

Example 1

In the test, a soil sample is collected from Wenshan, a soil microorganism trapping method is adopted to culture and separate candidate biocontrol bacteria, a living organism biological test system is used for evaluating the capacity of the candidate biocontrol bacteria for preventing and controlling tobacco bacterial wilt in a laboratory, and finally the disease control capacity of biocontrol is further verified in a greenhouse, and the specific method comprises the following steps:

the preliminary stage preparation work of the test mainly comprises the steps of tobacco seedling culture, microorganism trapping culture, pathogenic bacteria culture and the like.

Float seedling raising

The method is characterized in that a diseased tobacco variety, namely Honghuadajinyuan, is taken as a test object, and tobacco seedlings are cultivated to 4-5 leaf stages through floating seedling.

Trapping and separating of microorganisms

Removing impurities and larger blocks from a soil sample, putting the soil sample into a glass culture dish with the diameter of 120mm, wherein the thickness of a soil layer is about 1.5cm, and wetting the soil with distilled water by adopting a titration flask;

preparing a microorganism trapping device: firstly, coating glue on the edge of a microporous filter membrane with the diameter of 50mm and the aperture of 0.45 mu m, and placing a stainless steel flat-bottom gasket on the microporous filter membrane; then 3mL of solid medium (1.2% gellan gum and 1.0% vitamins) was added to the inner cavity of the gasket; coating glue on the upper surface of the metal washer, and covering another microporous filter membrane with the pore diameter of 0.45 μm;

placing the microorganism trapping device on the soil moistened in a glass culture dish according to the method, slightly compacting the device to ensure that the microporous filter membrane is fully contacted with the soil, completely covering the device with the residual soil, and moistening the soil again by using distilled water by adopting a titration flask;

covering the culture dish, sealing the culture device with a sealing film, culturing in an incubator at 30 deg.C for 7d, observing soil humidity, and supplementing with sterile water if soil humidity is low;

taking out the culture device from the incubator, mashing the solid culture medium, adding 3mL sterile water, standing for 10min, and diluting to 10^-4；

Get 10^-4、10^-5The bacterial liquid was spread on oligotrophic medium CN containing 0.1% casamino acid, 0.1% nutrient broth, 1.5% agar, 5 dishes each gradient coated, blow dried on a clean bench, and cultured in an incubator at 30 ℃ for 7 days.

Candidate biocontrol bacterium culture

Single colonies growing on the oligotrophic medium CN were picked and inoculated into a test tube containing 2.5mL of LB liquid medium (1% tryptone, 0.5% yeast extract, 1% sodium chloride and 0.5% sucrose), and subjected to shaking culture at 28 ℃ and 225r/min for 48 hours.

Cultivation of pathogenic bacteria

Activating tobacco ralstonia solanacearum on the surface of a TTC culture medium (1% peptone, 1% glucose, 0.1% casein hydrolysate, 1.5% agar and 0.005% triphenyltetrazolium chloride (TTC)) from an ultra-low temperature refrigerator at-80 ℃, and placing the surface in a constant temperature incubator at 28 ℃ for culturing for 36-48 h;

selecting a typical bacterial colony which has a wider white edge and stronger fluidity and is pink or light red dilute liquid in the middle, inoculating the typical bacterial colony into a triangular flask containing 100mL of CG liquid culture medium (1% peptone, 1% glucose and 0.1% casein hydrolysate), and placing the triangular flask in a constant-temperature shaking culture at 28 ℃ and 225r/min for 24 hours;

diluting 100 μ L to 10^-7Taking 100 μ L of 10^-5、10^-6、10^-7The dilution was spread on TTC plates and the colony morphology was observed and the number of colonies counted after 48 h.

The screening and evaluation of the tobacco bacterial wilt biocontrol bacteria are mainly divided into three stages of indoor primary screening and secondary screening and greenhouse verification control effect, and the method specifically comprises the following operations:

step S1, primary screening for bioassay

Tobacco seedling treatment: taking out the standby tobacco seedlings from the seedling raising pool 1d before the seedlings, airing and floating the tray, damaging the two sides of the root of each tobacco seedling, which are 1.5cm away from the center of each tobacco plant, by using an aseptic surgical blade the next day, dividing the tobacco seedlings into a test group and a control group, wherein each group comprises 2 tobacco seedlings, and a plurality of treatment groups and control groups are arranged.

And (3) biocontrol bacteria pretreatment: inoculating 1mL candidate biocontrol bacteria to the test group, and inoculating equal volume of LB culture solution to the control group;

tobacco seedling root suspension culture: placing a piece of thick plastic cloth 3 with the size larger than that of a floating disc on a culture shelf in a constant-temperature artificial climate room at 28 ℃, placing 5 disposable culture dishes 2 on 4 corners and the center of the plastic cloth 3 as supports (figures 2 and 3), placing the floating disc 1 on the plastic cloth for culture for 1d, and watering by a water spraying device in the morning, noon and evening, wherein the watering amount is suitable for preventing water in holes of the floating disc from dripping;

and (3) pathogen inoculation: after the biocontrol bacteria are pretreated for 1d, 0.5mL of 10-time diluent of the pathogenic bacteria is inoculated to the test group and the control group, the test group and the control group are continuously cultured in a constant-temperature artificial climate room at the temperature of 28 ℃ for 15-20 d, and watering and moisturizing are carried out by a water spraying device for three times in the morning, in the middle and at night;

and (4) observing and recording: observing the disease incidence of the test group and the control group, when the disease incidence of the control group is more than 80%, recording the disease incidence of the tobacco plants of the test group, wherein the value of the tobacco plants is 1 minute, the value of the tobacco plants which are diseased but not withered is 0.5 minute, the value of the tobacco plants which are withered and dead is 0 minute, the value of the tobacco plants processed by each test bacterium is the sum of the values of the two tobacco plants, and selecting the strain with the highest value among the test bacteria as the potential biocontrol bacterium for indoor repeated screening.

The operation steps of the raw test rescreening of the step S2 are the same as the raw test prescreening of the step S1 except for the following tests.

The test strain is potential biocontrol strain obtained by primary screening of step S1;

increasing the number of treated tobacco plants, and treating 8 tobacco seedlings in the treatment group and the control group;

disease occurrence of tobacco plants in each treatment group was investigated 10 and 20 days after the inoculation of ralstonia solanacearum.

Step S3, greenhouse verification

And (3) experimental setting: performing a test in a greenhouse with a temperature of 28-30 ℃, setting a ralstonia solanacearum treatment group and a control group (irrigating an equal-volume LB culture medium and tap water), and repeatedly treating for 3 times each time, wherein 10 tobacco plants are repeatedly treated each time;

and (3) culture of test strains: culturing biocontrol bacteria with LB liquid culture medium (1% tryptone, 0.5% yeast extract, 1% sodium chloride and 0.5% sucrose) at 225r/min and 30 deg.C for 48 hr; culturing pathogenic ralstonia solanacearum with CG liquid culture medium (0.1% acid hydrolyzed casein, 0.5% glucose and 2% peptone), and shake-culturing at 225r/min and 30 deg.C for 24 hr;

transplanting tobacco seedlings: uniformly mixing the red soil and the organic matter according to a ratio of 3:1, transplanting tobacco seedlings, wherein the tobacco seedlings are secondarily cut leaves, and culturing for about 50 d;

inoculation: diluting 250mL of biocontrol bacteria fermentation liquor by 25 times after transplanting, irrigating 200mL of diluent into roots of each tobacco plant, and treating a control group by using an equal volume of LB diluent; the next day, the CG medium was shaken for 24h and diluted 100-fold, and 100mL of the ralstonia dilution was inoculated per strain.

Survey and statistics: disease index was investigated every 7 days after inoculation, and 5 consecutive investigations were performed. The morbidity, disease index and prevention and treatment effect of the tobacco bacterial wilt are calculated according to the following formula: incidence rate is equal to the total number of diseased plants/investigation plants multiplied by 100%; disease index [ case number of strains)/(highest number of strains × total number of strains) ] × 100; the prevention and treatment effect is (contrast disease index-treatment disease index)/contrast disease index x 100%. The disease index is investigated according to the tobacco disease grading and investigation method of the tobacco industry standard of the people's republic of China (GB/T23222-2008), and the disease grading is as follows: the disease-free state of the whole plant is 0 grade, the withering of the leaves below one half of the diseased side is 1 grade, the withering of the leaves from one half to two thirds of the diseased side is 3 grade, the withering of the leaves above two thirds of the diseased side is 5 grade, the complete withering of the leaves of the diseased plant is 7 grade, and the basic withering of the diseased plant is 9 grade.

Results and analysis

And (3) test results: soil bacteria are separated from 50 soil samples collected from wenshan state in Yunnan province by adopting a soil bacteria trapping culture method, 5 strains with certain control effect in a greenhouse are obtained through primary screening of bioassay, secondary screening and secondary evaluation in the greenhouse, the value of all 5 strains in the primary screening in the greenhouse is more than or equal to 1.50, and certain disease prevention capability is shown in the first investigation (10dpi) of the secondary screening in the greenhouse. The results of greenhouse bioassay show that 100mL of 10 is inoculated in the greenhouse⁷3 strains of the CFU/mL ralstonia solanacearum 35d with the serial numbers of 11E4, 22-E5 and 4-4 still have the control effect of more than 40 percent. The results prove that the biocontrol bacteria with the disease control capability can be obtained by screening through indoor primary screening, secondary screening and greenhouse secondary evaluation by using a living body bioassay method.

TABLE 1 preventive and therapeutic effects on tobacco bacterial wilt by 5 biocontrol bacteria in example 1

Note: assigning value to each tobacco during primary screening, wherein the value of the health of each tobacco is 1.00, the value of partial wilting of each tobacco is 0.5, and the value of withering of each tobacco is 0.00; recording the number of the tobacco plants which survive in the secondary screening; in greenhouse evaluation, disease grades are investigated every 7d, and disease indexes are calculated; in the table, the control effect is the control effect of the treatment group relative to the control CK when the pathogenic bacteria 35d is inoculated.

Example 2

Example 2 the procedure was the same as in example 1 except for the following tests and results.

The soil samples to be tested were collected from tobacco-planting soil in Lincang City.

And (3) test results: collecting tobacco planting soil from tobacco fields in Lincang City Linxiang district, Shuangjiang county, Cangyuan county, Fengqing county and cloud county, separating soil bacteria by using a soil microorganism trapping method, and screening 5 strains with certain control capacity on tobacco bacterial wilt from 1248 strains of soil bacteria through indoor primary screening, secondary screening and greenhouse potting test, wherein the greenhouse control efficiency of 3 strains with the numbers of 56D2, 65D6 and 66C8 is more than 50 percent, so that the tobacco bacterial wilt control method has certain control potential. Similar to the results in example 1, the 5 strains screened in example 2 all have the assignment value of 1.50 or more in the indoor primary screening, and 3 strains such as 65D6, 66C8, 7E4 and the like show better disease control capability in the indoor secondary screening.

TABLE 2 biocontrol effect of 5 biocontrol bacteria on tobacco bacterial wilt in example 2

Note: assigning value to each tobacco during primary screening, wherein the value of the health of each tobacco is 1.00, the value of partial wilting of each tobacco is 0.5, and the value of withering of each tobacco is 0.00; recording the number of the tobacco plants which survive in the secondary screening; in greenhouse evaluation, disease grades are investigated every 7d, and disease indexes are calculated; in the table, the control effect is the control effect of the treatment group relative to the control CK when the pathogenic bacteria 35d is inoculated.

Example 3

Example 3 the procedure was the same as in example 1 except for the following tests and results.

1. The soil sample to be tested is collected from tobacco planting soil in the red river;

2. the disease grade and disease technical disease index are investigated when the control effect is repeatedly screened indoors;

3. when the control effect of potential biocontrol bacteria is evaluated by greenhouse potting, tobacco strains treated by adding control medicament thiabendazole copper and LB10 times of diluent are used as positive control and blank control.

And (3) test results: the method comprises the steps of adopting a soil bacteria trapping method, separating soil bacteria from tobacco-planting soil in Maitreya, Jianshui, Luxi, Kaiyuan and Shipingxian in red river, and finally obtaining 5 tobacco bacterial wilt biocontrol bacteria with certain control capacity through indoor primary screening, secondary screening and greenhouse potting. The evaluation values of 5 strains obtained by screening are more than or equal to 1.50 during indoor primary screening; the disease indexes of the tobacco strains treated by the 5 strains in the indoor repeated screening are all above 60 when the tobacco strains are inoculated for 20 days, which shows that the biocontrol bacteria can only delay the occurrence of diseases when the diseases are serious. In a greenhouse pot experiment, the control effect of 3 strains of bacteria with the numbers of 221D2, 221C8 and 219B1 is more than 38%, the control effect of the 3 strains of bacteria is better than that of a control medicament, namely thiabendazole, and the control effect of the thiabendazole is 31.02%. The results show that the biocontrol bacteria with certain control effect can be obtained by separating soil bacteria by a soil microorganism trapping method and then carrying out 3 times of living body bioassay such as indoor primary screening, secondary screening, greenhouse potted plant evaluation control effect and the like.

TABLE 3 biocontrol effect of 5 biocontrol bacteria in example 3 on tobacco bacterial wilt

Note: assigning value to each tobacco during primary screening, wherein the value of the health of each tobacco is 1.00, the value of partial wilting of each tobacco is 0.5, and the value of withering of each tobacco is 0.00; investigating the disease grade of tobacco plants during secondary screening, and calculating disease indexes; in greenhouse evaluation, disease grades are investigated every 7d, and disease indexes are calculated; in the table, the control effect is the control effect of the treatment group relative to the control CK when the pathogenic bacteria 35d is inoculated.

Example 4

The bacteriostatic zone of the strain was measured by plate-confrontation culture. The operation steps are as follows: gradient dilution of Ralstonia solanacearum cultured in CG medium (0.1% acid hydrolyzed casein, 0.5% glucose and 2% peptone) for 24h to 10^-4(ii) a Placing 100 μ L of the diluted solution on the surface of CGA (0.1% acid hydrolyzed casein, 0.5% glucose, 2% peptone, and 1.5% agar) culture medium, uniformly coating with coating strain, and blow-drying in ultra-clean work; selecting a single colony to be inoculated on the surface of a culture medium containing ralstonia solanacearum, observing the bacteriostasis condition of each strain after culturing for 2-3 days, culturing the strains with the bacteriostasis effect by using a four-point method in opposition, and measuring the bacteriostasis circle of the strainsAnd a zone of bacteriostasis.

And (3) test results: in order to preliminarily verify the disease prevention mechanism of the biocontrol bacteria screened in the examples 1, 2 and 3, the inhibition capacity of the 15 potential biocontrol bacteria on the tobacco ralstonia solanacearum is detected by adopting a plate confrontation method, and the result shows that only the strains numbered 4-4 have the bacteriostasis function and the bacteriostasis bandwidth is 0.8 cm. The rest 14 strains of bacteria have no inhibition capacity on the ralstonia solanacearum, and the 14 strains of bacteria are supposed to possibly play a biological control role through non-antagonistic action. The results show that the antagonistic bacteria in the conventional screening can be obtained by adopting the invention, and the biocontrol bacteria without antagonistic action can also be obtained by screening.

The scope of the present invention is not limited to the above-described embodiments, which are intended to help explain and illustrate the present invention, but not to limit the scope of the present invention, if it is designed to be the same as or substituted by the equivalent design of the present invention, and fall within the scope of the present invention as claimed.