Most widely used biocontrol agent is

Answer: Option A

The most widely used biocontrol agent is Pseudomonas florescence.
P. fluorescens is a potential agent for biocontrol which suppress plant diseases by protecting the seeds and roots from fungal infection.
They are known to enhance plant growth promotion and reduce the severity of many fungal diseases. Pseudomonas spp. have been reported to have the potential to improve plant biomass, relative water content, leaf water potential, and root adhering soil/root tissue ratio.