Effects of pesticides on soil microbial population and preliminary screening of resistant strains

  Objective  The dominant strains with degradation ability to dimethoate (organic phosphorus), beta-cypermethrin (pyrethroids) and imidacloprid (neonicotinoid) were screened and the effects of the above pesticides on the growth of soil microbial populations were explored.

  Method  The sensitive bacteria were screened out by artificial application, and the phenotypic characteristics and 16S rDNA of the dominant bacteria with certain resistance to pesticides were identified by dilution coating method and continuous streaking method.

  Result  The dominant bacteria screened from the soil after pesticide treatment were mainly Bacillus, Chryseobacterium, Pseudomonas and Acinetobacter; C3 strain in Bacillus did not have colonies in the soil treated with 4.000 g/L dimethoate and 0.100 g/L imidacloprid at high mass concentrations; strain C5 of Acinetobacter did not grow in 0.120 g/L, 0.040 g/L beta-cypermethrin and 0.100 g/L imidacloprid treatment groups; strain C6 of Pseudomonas did not grow in 4.000 g/L dimethoate and 0.050 g/L and 0.100 g/L imidacloprid-treated soils. Different concentrations of pesticides had different degrees of inhibition on soil colonies. The inhibition rate of bacterial and fungal colonies in soil was positively correlated with the concentration, and the inhibition rate showed a decreasing trend over time. On the 14th day, only 0.100 g/L imidacloprid treatment group did not recover to the normal level. In the treatment groups of dimethoate and imidacloprid in fungi, the number of fungal colonies in the low concentration soils on the 14th day was significantly higher than that in the high concentration soils (P < 0.05).

  Conclusion  There are dominant bacteria with certain resistance to dimethoate, beta-cypermethrin and imidacloprid pesticides in soils, which provide theoretical basis for directional culture of excellent strains. The inhibitory effects of different pesticides on the number of soil fungi and bacterial colonies are also different, and the inhibitory effects are as follows: imidacloprid > dimethoate > beta-cypermethrin. Moreover, imidacloprid has the highest inhibitory effect on the number of soil bacteria, and has little effect on soil fungi.