Biological characterization of Papaya ringspot virus pathotypes

Papaya ringspot virus (PRSV), a definitive member of the ‘Potyviridae’ family and the genus ‘Potyvirus’ is a major limiting factor affecting papaya and cucurbits in various parts of the world, including the Indian sub-continent. Two pathotypes of PRSV, papaya infecting (P) or non-papaya infecting (W) have been recognized. To study the prevalence and association of PRSV pathotypes in India, glass house and laboratory experiments were conducted at Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi. The results revealed association of Papaya ringspot virus (PRSV) with infected papaya (Carica papaya) and sponge gourd (Luffa cylindrica) samples collected from IARI experimental fields and it was confirmed by leaf-dip electron microscopy, bio-assay (host range) and immuno-assay (ELISA) studies. Based on the bio-assay, the virus isolates from papaya and sponge gourd were classified as P and W pathotypes respectively. Pathotype P could infect members of the family Caricaceae and Cucurbitaceae, while W pathotype could infect only Cucurbitaceous hosts. Both localized and systemic infection was observed on Cucurbitaceous hosts for pathotype W, while only localised infection was observed in few cucurbits for pathotype P. Pathotypes P and W collected from Delhi were unable to induce local lesions on Chenopodium quinoa and C. amaranticolor. Though some of the Cucurbitaceous hosts like ridge gourd, pumpkin, watermelon and muskmelon supported multiplication of pathotype P, yet pathotype P was more adapted to papaya, while pathotype W to Cucurbitaceous hosts.