The smallest plant pathogenic agent is

Solution(By Examveda Team)

The smallest plant pathogenic agent is Viroid.
Viroids are small single-stranded, circular RNAs that are infectious pathogens.
The first discoveries of viroids in the 1970s triggered the historically third major extension of the biosphere to include smaller lifelike entities after the discoveries in 1675 by Antonie van Leeuwenhoek.
viroids are composed of nucleic acid, they do not code for any protein. The viroid's replication mechanism uses RNA polymerase II, a host cell enzyme normally associated with the synthesis of messenger RNA from DNA, which instead catalyzes the "rolling circle" synthesis of new RNA using the viroid's RNA as a template.