| Microorganisms play an important role in the formation of soil aggregates.There have been many reports about the effects of extracellular exopolysaccharides(EPS)produced by microorganisms on the formation of water-stable soil macro-aggregates,but there are few studies on the disease-resistant effects of plants.Screening strains with high exopolysaccharides yield and high potato scab inhibition from soil samples,and providing candidate strains for preparing soil improved disease-resistant functional microbial agents.In this study,the plate confrontation method and anthrone sulfate method were used to screen out the strains which are antagonistic to Streptomyces scabrae and have high exopolysaccharides production.The classification status of the strains was determined by electron microscope observation,physiological and biochemical analysis and 16S rRNA gene sequence determination,and their phosphorus and potassium dissolving ability,salt and alkali tolerance and growth promoting effect were analyzed.The soil culture experiment was used to test the influence of the strains on the formation of soil aggregates.Pot experiment verified the control effect of the strain on potato scab.The following experimental results are obtained:1.Three strains with good antagonistic effects against Streptomyces scabra and an exopolysaccharides yield greater than 500 mg/L were selected,named A-5,XJ-3,and KW3-10,and identified as Bacillus licheniformis,Bacillus atrophaeus,and Bacillus halotolerans.Under scanning electron microscopy,it was found that all three strains of bacteria were rod-shaped,with blunt rounded ends and filamentous secretions around them,and Gram staining was positive.2.Strains A-5 and KW3-10 can grow under the condition of NaCl concentration of 1%-9%.XJ-3 and KW3-10 can tolerate the high salt environment with NaCl concentration greater than 11%.In the environment of pH 5-7,all three strains can grow normally,and KW3-10 can tolerate the extremely high alkaline environment of pH 11..3.After the strains A-5,XJ-3 and KW3-10 were cultured for 24 h,the IAA yields were 2.68,8.09 and 25.58mg/L,respectively.A-5 has good phosphorus dissolving ability.Inoculating potato seedlings with bacteria can obviously promote the growth of potato.SPAD value,plant height and stem diameter of A-5 treatment increased by 23.42%,21.35%and 20.73%respectively compared with the control.The SPAD value,plant height and stem diameter of XJ-3 treatment increased by 17.00%,28.83%and 36.96%respectively compared with the control.The SPAD value,plant height and stem diameter of KW3-10 treatment increased by 29.15%,34.81%and 56.54%respectively compared with the control.4.The soil culture experiment showed that the proportion of water-stable aggregates with soil particle size larger than 2 mm in the treatment groups inoculated with A-5,XJ-3 and KW3-10 increased by 1.97%,0.53%and 1.60%respectively compared with CK,and the differences reached extremely significant levels(P<0.01).The proportion of soil aggregates with particle size larger than 0.25 mm increased by 4.07,2.14 and 3.16 times compared with CK,among which XJ-3 and KW3-10 treatments reached significant levels(P<0.05).Compared with CK,the content of soil polysaccharide in treatments A-5,XJ-3 and KW3-10 increased by 28.87%,21.09%and 12.93%respectively,and the three target strains could significantly reduce the soil pH value.5.Applying bacterial suspension of A-5,XJ-3,and KW3-10 strains to potted potato seedlings,all three strains of bacteria could reduce the disease index of potato scab,with control effects of 68.68%,62.72%,and 60.24%,respectively.6.The sensitivity of the target strains to 15 chemical fungicides and biopesticides commonly used in agricultural production was measured.The three strains were not sensitive to chunleimycin,pyrazolin,flusilazole,avermectin,bifermethrin,acetamiprid,carbendazim,thiophanate-methyl,isocarburon,thiamethoxam,mesobiotin,and flubactam.Their growth and development were not affected.All three strains of bacteria could not grow normally around the filter paper coated with chlorothalonil,while strains A-5 and KW3-10 could grow normally around the filter paper coated with chlorothalonil,but XJ-3 was sensitive to chlorothalonil.7.Through broad-spectrum resistance analysis,it was found that three antagonistic bacteria had certain antagonistic effects against Alternariasolani,Fusariumoxysporum,and Rhizoctoniasolani.Among them,the bacteriostatic rates of strain A-5 against the above three pathogenic bacteria were about 21.42%,40.87%,and 5.26%,respectively.The bacteriostatic rates of strain XJ-3 were about 34.65%,36.08%,and 58.33%,respectively.The bacteriostatic rates of strain KW3-10 were 63.51%,68.87%,and 47.53%,respectively.Strains A-5,XJ-3,and KW3-10 have good control effects on potato scab and promote the formation of soil aggregates.They can all be used as candidate strains for highly effective composite functional fungicides,with good application prospects. |
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