| Heteroderaglycines Ichinohe(SCN)is an important plant parasitic nematode and distributed in soybean production areas worldwide.It is one of the most devastating soil-borne pathogens in soybeans.This study presents theisolation and screening of the potential biocontrol bacteria against soybean cyst nematode from rhizosphere of the diseased soybean infected by SCN in Hangzhou city ofZhejiang province,Suzhou city of Anhui province,and Taigu County of Shanxi Province.Pot trails and bioassays were conducted to verify the biocontrol efficacy of studied bacterial populations.Additionally the main physiological and biochemical characteristics of biocontrol bacterial strains were also investigated.The main results of the study obtained are as follow:1.112 bacterial strains were isolated and screened from the rhizosphereof diseased soybean plants.For biocontrol evaluation strains were selected based on different colony characters.In vitro experiments showed that there were 8 bacterial strains that had certain inhibitory effects on egg hatching and the activity of second stage juveniles(J2)of H.glycines.Among them,strain A2-4,HZ-6,and SH-1 had significant effects,the inhibitory rates of the three bacterial strains on egg hatching were 89.9%,92.4%and 93.2%,respectively.The mortality rates of the second stage juveniles were 74.2%,66.3%and 72.6%,respectively.Inhibitory effect was observed to be weakened with the increase in dilution concentration.In addition,Itwas found that these bacterial strains have certain inhibitory effectson Aphelechoides besseyi and Bursaphelechus xylophilus,both of them have important influence on agricultural and forestry production.For example,strain A2-4 observed to be highly toxic to Bursaphelechus xylophilus,with a fatality rate of 70.9%and Aphelechoides besseyi of 52.3%.2.Based on morphological and molecular characteristics,combined with MBT analysis and FAME analysis,A2-4 strain was identified as Bacillus megaterium,HZ-6 as B.firmus and SH-1 as B.endophytic.3.The bioassay results showed that the three bacterial strains and their mixture had good control effect on soybean cyst nematode.The inhibition rate of the fermentation filtrate of B.megacillus(A2-4)strain on the SCN was up to 72.3%.The inhibition rate of B.firmus(HZ-6),B.endogenous(SH-1)and mixed bacterial solution(1:1:1)was 57.4%,52.2%and 64.1%,respectively.Plant growth promoting effects of these bacterial strain was also observed,It had significant effects on plant height and shoot weight as compared to control.The higher effect of plant height and shoot weight was observed in B.megalosporus(A2-4)which was 24.7%and 31.0%followed by B.firmus(HZ-6)which was 18.8%and 16.9%and B.endogenous(SH-1)which was 11.5%and38.5%,while for mixed bacterial solution(1:1:1)it was 7.8%and 22.9%,Additionally the length and weight of fresh root had showed a certain increase.4.The physiological and biochemical characteristics showed that the optimal carbon source of strain A2-4 was alpha-lactose,followed by sucrose.The optimal nitrogen source was ammonium chloride while the growth temperature is 25 to 35 ?,and the pH is 7.At 10%NaCl concentrationthe growth of strains appeared to be inhibited.In terms of carbon source utilization,strains HZ-6 and A2-4 showed consistent performance.When the nitrogen source is ammonium sulfate,it is most beneficial to the bacterial growth.For both bacterial strains the optimum growth temperature was 25 ? and the pH was 7 while at 10%NaCl concentration strains failed to survive.As for strain SH-1,sucrose was the optimal carbon source,however,it cultured well on the glucose,maltose and mannitol mediums.The effects of ammonium chloride,ammonium sulfate and urea on SH-1 growth were not significantly different.The optimal growth temperature for this strain was 35 ?,and the pH was 7,while this strain can still cultured at 10%NaClconcentration. |
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