Screening Of Antagonistic Bacteria Against Potato Black Scurf And Study On Its Biocontrol Mechanism

Potato black scurf is a soil-borne fungal disease caused by Rhizoctonia solani,which seriously affects the yield and quality of potato.Presently,the prevention and control of potato black scurf mainly adopts chemical control,but the long-term use of chemical agents will affect soil quality,drug residues,endanger human health,and so on.Biocontrol is an effective way to control soil-borne diseases and an important part of green prevention and control.The purpose of this study was to screen the bacterial strains with strong antagonistic effect on potato black scurf,and to reveal the prevention and control mechanism of antagonistic bacteria on potato black scurf through pot experiments.The test results are as follows:1.A total of 303 bacterial strains were isolated from potato rhizosphere soil by dilution plate method.A bacterial strain KSD17 with the strongest antibacterial activity was screened by plate confrontation.The inhibition diameter and inhibition rate were 11.76 mm and 78.91%,respectively.Antagonistic strain KSD17 colony is opaque milky white,no wrinkles,viscous,no pigment production,irregular edge.Combined with physiological and biochemical characteristics and molecular biological identification,strain KSD17 was identified as Paenibacillus polymyxa.2.In order to improve the reproduction and bacteriostatic ability of the antagonistic strain KSD17.The optimum fermentation condition were optimized by taking the absorbance value of the antagonistic strain KSD17 at OD₆₀₀ and the inhibition rate of the sterile fermentation broth against Rhizoctonia solani.The results showed that the optimum fermentation medium was mannitol 8 g,tryptone 10 g,yeast extract 5 g,Na Cl 10 g,H₂O 1 000 m L.The optimum culture conditions were as follows:original p H 6,culture temperature 30°C,rotation speed 200 r/min and fermentation time 40 h.3.The results of pot experiment showed that the antagonistic strain KSD17 had good control effect on potato black scurf,and the control effect increased with the increase of inoculation amount.The control effect of reagent amount was 33.08%-66.17%.4.The biocontrol mechanism of antagonistic strain KSD17 against potato black scurf was studied.The results showed that the metabolites of antagonistic strain KSD17 inhibited the mycelial growth of Rhizoctonia solani.The mycelia of Rhizoctonia solani showed wrinkles,depressions and uneven contents.The dry weight and wet weight of mycelia decreased by 29.78%and 57.14%respectively compared with the control.The strain can produce protease,cellulase and glucanase,destroy the cell membrane of pathogenic bacteria,and make intracellular soluble sugar,soluble protein and nucleic acid exosmosis.The results of plant rhizome defense enzyme activity determination showed that the antagonistic strain KSD17 could induce the increase of SOD,POD,CAT,PPO and PAL activities in potato rhizomes,which were 20.10%,80.77%,50.97%,29.33%and 31.57%higher than those of the control,respectively.The antagonistic strain KSD17 significantly increased the morphological indexes of potato plants and the yield of potato.Appropriate inoculation amount could increase the tuber weight of potato by 39.12%.Strain KSD17 could induce the resistance of potato plants and significantly promote the growth of potato plants.The results of the determination of soil colony number and soil enzyme activity of plant roots showed that the antagonistic strain KSD17 could reduce the number of fungi and Rhizoctonia in soil and increase the number of bacteria.The antagonistic strain KSD17 significantly increased soil catalase,phosphatase and invertase activities by 12.05%,76.80%and 6.69%,respectively,compared with the control,and promoted the growth of potato plants.In summary,Paenibacillus polymyxa KSD17 had good control effect on potato black scurf,promoted plant growth,improved plant system resistance and soil enzyme activity.The results laid an important theoretical foundation for the development and application of biocontrol agents against potato nevus.