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 melon-infecting SLCCNV through its genome, infectious clone and transmission.

 

Apple stem pitting virus (ASPV) is an important causal agent of pear diseases.  Nowadays, the infection status and molecular characteristics of the virus in old pear trees have never been investigated.  In this study, we provide the first complete genome sequence of an ASPV isolate LYC from an over 300-year-old tree of a local Pyrus bretschneideri cultivar ‘Chili’ specifically grown at Laiyang area in China.  ASPV-LYC possesses a chimeric genome consisting of 9 273 nucleotides excluding a poly(A) tail at its 3´ end and harboring a recombination region in its open reading frame (ORF1) with Aurora-1 and KL9 identified as the major and minor parents.  Western blot analysis with antisera against recombinant coat proteins (CPs) of three ASPV isolates from pear indicates that ASPV-LYC is serologically related to these ASPV isolates, but with differential activities.  Further biological tests on indicator plants of Pyronia veitchii show that ASPV-LYC can induce serious leaf and stem symptoms as other ASPV isolates.  The results provide an important information for understanding molecular evolution of ASPV and suggest a need to prevent dissemination of the isolate among pear trees.