| Maize cob rot is a common agricultural disease that affects maize between sowing and harvest,causing serious effects on quality and yield,and the pathogenic bacteria also produce toxins that pose a threat to human and livestock health.At present,chemical control is still the main measure.Chemical control has the advantages of quick results and ease of use.However,the use of chemical pesticides may lead to the development of resistance to the pathogen,and cause serious harm to the environment,so it is necessary to carry out research on biological control.In this experiment,Strain N20 was isolated and screened with good biocontrol effect on Fusarium graminearum,and was subjected to identification,determination of inhibition activity,determination of inhibition spectrum,optimisation of fermentation conditions,stability of inhibition activity of fermentation broth and biocontrol potential.The main results are as follows:1.Thirty strains of bacteria were isolated from the soil by dilution coating method,and seven strains were screened out with an inhibition rate of more than 50% on the mycelial growth of Fusarium graminearum by plate confrontation method,among which the inhibition rate of strain N20 reaches 85.63% with the best suppression effect on the mycelial growth of Fusarium graminearum.2.The N20 strain was identified as Paenibacillus polymyxa by morphological,physiological,biochemical and molecular identification.3.The inhibitory effect of strain N20 on the mycelial growth of 10 tested plant pathogenic fungi was determined by the plate confrontation method,among which the N20 strain had the best inhibitory effect on the mycelial growth of Fusarium graminearum,and the mycelial growth inhibition rate reached 90.91%.4.This study investigated the impact of N20 sterile filtrate and fermentation supernatant on the growth of Fusarium graminearum mycelium and spore germination.Results showed that the addition of sterile filtrate and fermentation supernatant led to deformities in the mycelium,including top swelling and hyphae rupture.Additionally,the N20 strain’s sterile filtrate and fermentation supernatant had a significant inhibitory effect on the germination of conidia of Fusarium graminearum.At 12 hours,the inhibition rates of conidia germination were 56.01% and 75.45% for sterile filtrate and fermentation supernatant,respectively,when the concentration was 50%.When the concentration was 10%,the inhibition rates of conidia germination were 27.37% and 42.71% for sterile filtrate and fermentation supernatant.The N20 strain fermentation broth and bacterial suspension at 10%showed inhibition rates of 89.33% and 88%,respectively,on the mycelia of Fusarium graminearum when grown on solid medium.The addition of 10% sterile filtrate on the mycelia of Fusarium graminearum resulted in an inhibition rate of 25.73%.When grown under liquid culture conditions,the N20 strain showed an inhibition rate of 83.92% on the dry weight of Fusarium graminearum mycelium.5.The fermentation conditions of the N20 strain were optimized through the PlackettBurman test design,the steepest climbing method test design,and the Box-Behnken test design to determine the best conditions.The optimal conditions were found to be 7.5 g of yeast extract,25 g of sucrose,and 15 g of tryptone,with a p H of 7,temperature of 28°C,time of 24 h,rotation speed of 120 r/min,and an inoculum size of 3%.The optimized fermentation system was used to cultivate N20 strain,and the inhibition rate of 50% sterile filtrate on the growth of Fusarium graminearum mycelia reached 73.33%.6.The effects of three factors,namely p H,temperature and ultraviolet rays,on the stability of N20 fermentation broth were determined by mycelial growth rate method.The amount of sterile filtrate added was 33.33%;In terms of p H stability,the inhibition rate was 45.45% at p H=5,and 17.75% and 19.92% at p H=11,respectively,which was not conducive to the growth of N20 strains.After different temperature treatment,the inhibition rate was 41.33%at 30 °C,34.42% and 33.17% at 50 °C and 70 °C,respectively,and the inhibition rate was about 30% in the range of 50-121 °C,the bacteriostatic activity was basically the same,and the N20 strain sterile filtrate had good stability to temperature.In terms of UV stability,the inhibition rate of 0.5 h UV treatment was 45.78% in different UV treatment groups,and the inhibition rate was about 30% in 1.5-4 h treatment,and there was no significant difference in the inhibition effect,and the sterile filtrate of N20 strain had relative stability to ultraviolet.7.Crude protein was extracted by ammonium sulfate precipitation,and it was found that when the saturation of ammonium sulfate was 100%,the aseptic filtrate had the highest inhibitory rate on the growth of Fusarium graminearum mycelia with the addition of 33.33%,and the inhibition rate reached 55.84%.With the increase of ammonium sulfate saturation,the colonies of Fusarium graminearum changed obviously,and the colony color became white-yellow.The crude lipopeptide of N20 strain was extracted by acid precipitation,and the inhibition rate of Fusarium graminearum growth with 8.33% crude lipopeptide addition was 67.88%.8.N20 strains were detected in plant in vitro phosphorus,potassium,nitrogen fixation and iron philosophic functions,N20 strains all had phosphorus lysis,potassium solution,nitrogen fixation and iron philosis functions,but the effect was not very obvious.The results of the pot plant growth promotion experiment showed that N20 strain had no obvious growth promotion effect on maize.9.At the seedling stage of maize,the effects of N20 strain on the activity of defense enzymes and MDA content in maize leaves and roots were detected.The results showed that the activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)all increased first and then decreased,and the defensive enzyme activities in the 6th and 4th groups reached the highest values,among which the enzyme activity was the highest in the Fusarium graminearum conidia suspension treatment group.The trend in malondialdehyde(MDA)content is the same as the trend in defense enzyme activity,with MDA content being the highest value at 9 days and subsequently decreasing.The results showed that the N20 strain improved the disease resistance of maize.10.In the N20 strain pot control experiment,the disease rate of maize was inversely proportional to the amount of N20 bacterial liquid added.When the amount of N20 bacterial solution was 25 m L,the disease plant rate was 17.78%,and the disease plant rate was 71.44%,except for the pharmaceutical treatment group,the disease plant rate was the lowest and the disease plant rate was the highest.11.In the field control experiment of N20 strain,the N20 bacterial solution and Fusarium graminearum conidia suspension were inoculated on the same day in the treatment group and the N20 bacterial solution were inoculated first,and the Fusarium graminearum conidia suspension treatment group was inoculated 24 h later,except for the pharmaceutical experimental group,the N20 bacterial solution concentration 10 times group had the lowest disease index and the best prevention and control effect. |
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