Mixed Virus Infections in Rice

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Rice is one of the highest consumed food gains in the world and is a key commercial product in the world economy. However, recurring outbreaks of viral diseases in rice lead to a significant loss of yield and economy in several Asian, African, and Latin American countries. Mixed virus infections are common in field conditions. They often lead to synergistic enhancement of the pathogenicity of one or both infecting viruses. However, in certain cases, antagonistic interaction between the viruses leading to the suppression of infectivity of one by the other virus has also been reported. Out of all rice-infecting viruses, 4 pairs of viruses are known for being involved in mixed infection, where symptom development and pathogenicity of the diseases get synergistically enhanced. Rice tungro disease is one of the most wellknown diseases in this category that occurs due to simultaneous infection by the Rice tungro spherical virus and Rice tungro bacilliform virus and is responsible for major economic losses in South and Southeast Asia. On the other hand, mixed infection by Southern rice black-streaked dwarf virus and Rice ragged stunt virus came into the picture rather recently. Interestingly, all the mixed virus infections in rice are transmitted by insect vectors. Therefore, elucidating the complex interactions between the host-virus-vector pathosystems is pivotal for finding ways to control both single and mixed virus infections in rice.