Fig. (2) Entry and spread of plant virusesa. Insect vectors are generalist in nature and feed on different plants. b. Viruses are then released through the stylet of the insect into mesophyll cells primarily. c. Viruses then spread to neighbouring cells and enter a sieve tube to infect distant cells via plasmodesmata. Viruses may experience varying fitness in different cells of the plant. For example, in the given figure, the virus experiences high fitness in bundle sheath cell and cell ‘X’ as indicated by the replicative potential of the virus. ‘X and Y’ could be any other living cells of the plant.