Identification of Novel Begomoviruses Associated with Leaf Curl Disease of Papaya (Carica papaya L.) in India

Papaya (Carica papaya L.) is one of the most important fruit crops grown in tropical and subtropical regions of the world. Papaya leaf curl disease is one of the greatest concerns next to Papaya ring spot disease for India and the world. A survey was conducted during the year 2019 to 2021 for assessing the leaf curl disease incidence in five major papaya-growing districts of Karnataka State, India. The incidence ranged from 10 to 21 percent, with plants expressing typical begomovirus symptoms. Thirty-two virus-infected papaya samples (PLC-1 to PLC-32), collected from different farmer's fields, gave positive amplification for begomovirus detection. Based on the partial genome analysis, 13 representative papaya leaf curl isolates were selected for complete genome amplification by rolling circle DNA amplification (RCA). The RCA products were cloned, sequenced and analyzed. Based on the analysis and strain classification criteria for begomoviruses, five isolates (PLC-2, 3, 9, 11 and 18) were considered variants of Chilli leaf curl virus (ChiLCV). Isolate PLC-22 is considered a strain of ChiLCV, with 93.5% nt identity sharing. Similarly, isolate PLC-28 is considered a strain of Croton yellow vine mosaic virus (CYVMV), and isolates PLC-25 and PLC-31 were considered as strains of Papaya leaf curl virus (PaLCuV). Among the remaining four isolates, three (PLC-1, PLC-4 and PLC-7) share more than 91% nt identity among them and less than 91% nt identity with all other reported begomovirus isolates. Hence, they are considered to be isolates of the novel begomovirus, and the name Papaya leaf curl Bagalkote virus [India:Karnataka:Bagalkote:Papaya:2021] is proposed. One isolate (PLC-32) is also found to be distinct from all other begomovirus isolates, including the isolates in the current study also considered to be novel begomovirus, for which we propose the name Papaya leaf curl Haveri virus [India:Karnataka:Haveri:Papaya:2021]. The putative recombination analysis of all 13 papaya isolates showed that a major part of the viral genome was likely descended from the begomoviruses reported previously. This is the first report on the diversity and a distribution of the begomoviruses infecting papaya in Karnataka, India. The current investigation results revealed five major papaya-infecting begomoviruses (PaLCuBKV, ChiLCV, PaLCuV, CYVMV and PaLCuHV) in the sampled regions.