Mixed infection of plant viruses: diagnostics, interactions and impact on host

Globally, viral diseases cause huge economic losses in crops and their management is a big challenge to growers as well as researchers. Mixed infection is the existence of more than one virus in single plant, which results in varied symptoms at the same time. The presence of more than one virus always leads to difficulty in understanding the etiology of disease. Most of the viral diseases go unnoticed either due to the latent nature of infection of virus(es) or due to low severity of symptoms. But this might be true in case of single infection of the host by the concerned virus. When such viruses are seen causing infection in combination with other viruses at particular time, more severe disease symptoms can be observed. For any successful management of viral disease especially during mixed infection, detection and identification of plant viruses causative of the disease are of foremost importance. Several approaches like cocktail ELISA, multiplex PCR for known viruses and next-generation sequencing for both known and unknown viruses have been developed for detection of mixed infection of viruses. During mixed infection, several kinds of interaction commonly referred to as synergistic or antagonistic interactions are going on between and among the viruses, which aggravate the disease with more severe symptoms than with single infections. Here, we review the mixed infection of viruses, methods of detection, factors influencing, interactions and impact on plant during mixed infection.