Which among the following is a biocontrol agent?

The correct answer is Option (4) → All of these

Biocontrol means using living organisms to control plant diseases and pests, in place of chemical pesticides. Bacteria, fungi and viruses can all serve as biocontrol agents.

Option (1) Nucleopolyhedrovirus — Incorrect. Nucleopolyhedrovirus is a genus of baculoviruses that attack insects. It is a biocontrol agent, but it is not the only one in the list, so this option alone is incomplete.

Option (2) Trichoderma — Incorrect. Trichoderma is a free-living fungus of the root region that controls several plant pathogens. It is a biocontrol agent too, so this option alone is incomplete.

Option (3) Bacillus thuringiensis — Incorrect. Bacillus thuringiensis (Bt) is a bacterium whose spores are sprayed on plants to kill butterfly caterpillars. It is also a biocontrol agent, so this option alone is incomplete.

NCERT Extract:
Microbes as Biocontrol Agents – “… An example of microbial biocontrol agents that can be introduced in order to control butterfly caterpillars is the bacteria Bacillus thuringiensis (often written as Bt). … A biological control being developed for use in the treatment of plant disease is the fungus Trichoderma. Trichoderma species are free-living fungi that are very common in the root ecosystems. They are effective biocontrol agents of several plant pathogens. Baculoviruses are pathogens that attack insects and other arthropods. The majority of baculoviruses used as biological control agents are in the genus Nucleopolyhedrovirus.”