Effects of Beauveria bassiana and acephate on rice antioxidant status and soil nitrogen circulation

Beauveria bassiana is a common entomopathogenic fungus with a global distribution. Isolates of B. bassiana can antagonize a variety of soil and plant pathogens. At present, studies have focused on B. bassiana insecticidal mechanism and symbiosis with plants. In order to investigate the ecological safety of B. bassiana and its environmental behavior in paddy systems, we conducted a potted trial to evaluate the effects of different concentrations of B. bassiana spore suspensions and chemical pesticide (acephate) on the redox state of rice and the intensity of biochemical processes related to soil nitrogen circulation. B. bassiana were expressed with the egfp gene (green fluorescent protein gene) through transformation with a vector, and real-time polymerase chain reaction (PCR) was used to detect B. bassiana in rice grains. To accomplish this, B. bassiana specific DNA primers (eGPF-F1/ eGFP-R1) were designed after the green fluorescent protein sequence marked B. bassiana. Amplification of B. bassiana DNA yielded a single 289 bp-long product using the eGPF-F1/eGFP-R1 primers. The detection limit was 10 fg·μL^-1 of B. bassiana genomic DNA. The pot experiments consisted of seven treatments - CK (blank control group), CS (Chilo. suppressalis larvae), B1 (B. bassiana at 7.5×10⁴ spores·mL^-1 + CS), B10 (7.5×10⁵ spores·mL^-1 + CS), B100 (7.5×10⁶ spores·mL^-1 + CS), B1000 (7.5×10⁷ spores·mL^-1 + CS) and AE (acephate + CS). The results showed that B. bassiana stimulated the ammonification and nitrification of soils with maximum increases of 12.4% and 36.8%, respectively. Low concentration of B. bassiana facilitated denitrification, while high concentration inhibited denitrification. On the 10th day after treatment, acephate decreased ammonification, nitrification and denitrification rates by 18.6%, 45.3% and 27.5%, respectively. After inoculation with C. suppressalis and acephate application, ratios of AsA︰DHA and GSH︰GSSG reduced with decreasing antioxidant capacity. In contrast, B. bassiana treatment increased AsA︰DHA and GSH︰GSSG ratios. Changes in H₂O₂ content showed that C. suppressalis and acephate induced peroxidation, while B. bassiana reduced peroxidation intensity induced by C. suppressalis. Finally, B. Bassiana was not found in grains after RT-qPCR analysis. Overall, it was concluded that compared with chemical pesticide (acephate), B. bassiana was an effective and environment-friendly microbial pesticide.