The biological mechanisms associated with plant reactions to different levels of virosis (virus infection) can vary depending on the specific virus and plant species involved. However, in general, it is likely that the mechanisms involved in plant responses to lower levels of virosis may differ from those associated with higher levels of virosis.

When a plant is infected by a virus, it can initiate a series of defense mechanisms to try to combat the infection. These mechanisms include both non-specific and specific responses. The non-specific response includes the activation of cell-wall reinforcement, production of reactive oxygen species (ROS) and the production of pathogenesis-related (PR) proteins. This response is quickly activated and is not virus-specific.

At lower levels of virosis, the plant may primarily rely on its non-specific response mechanisms in order to combat the virus. However, as the virus infects more cells and the infection becomes more severe, the plant may then begin to activate specific response mechanisms, such as the production of viral-encoded silencing (VESP) genes, which inhibit viral replication, the activation of interferon signaling pathways and the production of the viral-induced small RNAs.

The specific response mechanisms are activated by the presence of viral dsRNA (double-stranded RNA) or viral replication intermediates, indicating the viral replication within the cells.

It's also important to note that in some cases, the plant may also develop mechanisms to tolerate the infection, allowing the virus to persist within the plant while still maintaining its growth and reproductive capacity.

In summary, at lower levels of virosis, plants may primarily rely on non-specific defense mechanisms, while at higher levels, specific defense mechanisms may be activated to combat the virus, however depending on the specific plant-virus system, the mechanisms could be different.