| In this paper,20 species of Trichoderma strains were isolated and purified from different plant rhizosphere soil samples by the dilution coating plate method.Through laboratory plate confrontation experiment,it was found that D1 strain had a strong inhibitory effect on Rhizoctonia solani,and the inhibition rate was 80.82%.Through fungistatic test of fermentation concentrate on Rhizoctonia solani,it was found that the D1 strain fermentation concentrate had a strong inhibitory effect on Rhizoctonia solani,and the inhibitory rate was 69.55%.Based on the results of the research,D1 strain was selected as Trichoderma for the biological control of Rice sheath blight,and was initially identified as Trichoderma brevicompactum morphologically and molecularly.After the D1 strain was tested against 8 plant pathogens,it was concluded that D1 strain had strong inhibition against 8 plant pathogens,the inhibition rate was 63.03%～95.18%.At 20～30℃ and pH 4～5,D1 strain had the best inhibitory effect on Rhizoctonia solani,and the inhibitory rates were 76.15%～80.70%and 78.57%～78.77%respectively.The five fungicides tested had different virulence to the mycelia growth of D1 strain,the EC50 value was 0.042～384.24 mg/L,but the inhibition rate was 75.8%～100%under the common concentration in the field.From the pot experiment of Rice sheath blight controled by strain D1,it was concluded that D1 strain did not cause rice disease,and could increase rice yield,improved by 27.41%compared to sterile water treatment,and promoted rice growth to some extent.D1 strain treatment had a high control efficiency on Rice sheath blight,the prevention effect ranged from 51.09%to 70.64%,in which the first treatment with D1 strain for 24 hours and then inoculation was the most effective,followed by the treatment with D1 strain at the same time,the first inoculation for 24 hours and then the treatment with D1 strain was the least effective.The setting rate,1000-grain weight and yield of rice treated with D1 strain were significantly higher than that treated with pathogen alone,the reduce production loss rate was 54.55%～96.37%.D1 strain had preventive and therapeutic effects on Rice sheath blight,and the preventive effect was better than therapeutic effects.According to the results of the study on the biocontrol mechanism of strain D1,it was concluded that strain D1 had the effects of antibiotic,competition,repetitive parasitic effect on Rhizoctonia solani,and could induce the resistance of rice and promote the increase of rice yield.The antibioactive substance of the fermentation concentrate of D1 strain had high stability to heat,prefers a slightly acidic environment,and was easily destroyed in a strongly alkaline environment,and it was not volatile.The increase of the defense enzyme activity in the rice plant was induced by the inoculation with Rhizoctonia solani only,but the defense enzyme activity in the rice plant was decreased by the treatment with Rhizoctonia solani and D1 strain,which was still higher than that of the control treated with only D1 strain and sterile water.D1 strain could not increase the chlorophyll content of rice leaves alone,but could increase the chlorophyll content of rice leaves treated with Rhizoctonia solani,but it did not exceed the control group without pathogen.In the study of the effects of different temperature,pH and PDA concentration on the growth and spore production of D1 strain,it was found that D1 strain grew fastest at 25～30 ℃,pH 6～8 and PDA concentration of 75%～100%,at 25℃,pH 7 and PDA concentration of 100%produced the most spores.After fermentation of D1 strain under different single-factor conditions and confrontation with Rhizoctonia solani,it was found that the best fermentation time was 3 d,the temperature was 25℃,and the liquid volume was 100 mL(250 mL),the initial pH was 6.2,the speed was 160 r/min,the carbon source was glucose 2.43%glucose,and the nitrogen source was peptone 0.32%,the inorganic salt was 0.13%of magnesium sulfate. |
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