A Sensitive Method for Detecting Beauveria bassiana, an Insecticidal Biocontrol Agent, Population Dynamics, and Stability in Different Substrates.

Abstract

Beauveria bassiana is a well-known insecticidal biocontrol agent. Despite its broad field applications, its survival, colonization, and stability under field conditions remained unclear, mainly due to the lack of a quick and reliable detection method. In this study, we developed a quantitative real-time PCR technology to monitor the stability and population dynamics of B. bassiana in different substrates (water, soil, and on the cotton leaves surface), different spores of B. bassiana applied on Chinese cabbage leaves surface, and the lethality of Pieris rapae spraying with different spores of B. bassiana. Our results showed a decreased concentration of B. bassiana DNA in all three substrates from the 1^st day till 9^th day of post inoculation (dpi) period, possibly due to the death of B. bassiana. After this decrease, a quick and significant rebound of B. bassiana DNA concentration was observed, starting from the 11^th dpi in all three substrates. The B. bassiana DNA concentration reached the plateau at about 13^th dpi in water and 17^th dpi in the soil. On cotton leaves surface, the B. bassiana DNA concentration reached the highest level at the 17^th dpi followed by a small decline and then stabilized. This increase of DNA concentration suggested recovery of B. bassiana growth in all three substrates. We found that the most suitable killing effectiveness of P. rapae was the 1.0 × 10⁷ spores/mL of B. bassiana. In summary, we have established a detection technology that allows a fast and reliable monitoring for the concentration and stability of B. bassiana under different conditions. This technology can benefit and help us in the development of proper management strategies for the application of this biocontrol agent in the field.