Molecular and biological characterization of melon-infecting squash leaf curl China virus in China

It has been reported that squash leaf curl China virus(SLCCNV) infects some Cucurbitaceae crops except for melon(Cucumis melo L.). A new disease of melon exhibiting severe leaf curl and dwarfing was observed in Hainan Province of China. In this study, the pathogen was identified as SLCCNV through biological and molecular characterization. The isolate(SLCCNV-HN) possess a bipartite genome, DNA-A(HM566112.1) with the highest nucleotide identity(99%) to SLCCNV-Hn(MF062251.1) pumpkin and SLCCNV-Hn61(AM260205.1) squash isolates from China, whereas DNA-B(HM566113.1) with the highest nucleotide identity(99%) to SLCCNV-Hn(MF062252.1). Phylogenetic analyses based on the full-length SLCCNV-HN DNA-A and-B sequences indicated that SLCCNV-HN melon isolate is clustered with SLCCNV-Hn pumpkin, SLCCNV-Hn61 and SLCCNV-SY squash isolates from southern China, forming an independent cluster. Infectious clone of SLCCNV-HN was constructed and the melon plants were inoculated and the infection rate is 100%, the systemic symptoms in melon showed identical to those of melon plants infected in fields. Additionally, melon plants transmission of this virus by Bemisia tabaci with a transmission rate of 95%(19/20) showed leaf curl and dwarf symptoms 15 days post transmission, thereby fulfilling Koch’s postulates. Analysis of genomic organization and phylogenetic trees indicated that SLCCNV-HN melon isolate belongs to the Begomovirus genus. To the best of our knowledge, this is the first characterization of meloninfecting SLCCNV through its genome, infectious clone and transmission.