Molecular Detection of Papaya ringspot virus and Associated Complexities in Papaya and Cucurbits

Papaya ringspot virus (PRSV), which is transmitted by aphids, is considered to be the major virus infecting papaya and cucurbits worldwide. In this study, we detected the virus and other associated pathogen complexities in papaya and cucurbits through polymerase chain reaction (PCR) assay. In one step reverse transcription (RT)-PCR tests, primarily both hosts were found to be positive for Potyvirus, as indicated by ~330 bp amplicon. The CP gene of PRSV‑P strain was detected in almost all tested papaya plants by producing an 850-bp band in gel electrophoresis. However, there was limited amplification found in cucurbit hosts. Since the papaya plants showed complex symptoms including leaf deformities, whitefly-transmitted geminivirus and phytoplasma were also tested in both host plants. Leaf samples collected from different locations in Bihar, India, showing the presence of PRSV‑P in most of the tested papaya samples, but limited presence in cucurbits. The presence of whitefly-transmitted geminivirus was noted in most mature cucurbits, but the lowest detection rate was recorded in papaya. The association of phytoplasma was also confirmed in four samples of papaya leaves by using universal primer of 16S rRNA gene in PCR. Although PRSV does not broadly infect cucurbitaceous hosts naturally, it is artificially transmitted in various cucurbits with up to 45% transmission in a controlled environment. The present findings suggested that the ringspot complexity can be explained by association with other pathogens, e.g., begomovirus and phytoplasma. Through the information obtained, it was revealed that the PRSV (P strain) is only associated with papaya; therefore, it appears that cucurbits play no role as a virus reservoir. The present studies will be supportive in understanding the epidemic factors of disease and in the formulation of need-based management strategies.