Studies On Geminiviruses Infecting Tomato And Euphorbia Pulcherrima In Guangxi

Geminiviruses are a group of plant viruses that have circular single-stranded DNA genomes packaged within twinned (geminate) particles. In recent years, geminiviruses have caused significant yield losses to many crops and are emerging as a serious crop threat in many parts of the world, so research on geminivirus samples collected in Guangxi province was carried out.Virus samples collected from tomato and Euphorbia pulcherrima in Guangxi were detected with triple antibody sandwich ELISA (TAS-ELISA) and/or PCR, detection results showed all the virus samples were infected by whitefly-transmitted geminiviruses. On the basis of these data, complete genomic structure of several virus isolates was further studied.The full-length DNA-A molecules from tomato sample G16, G18, G32 and G63 were cloned and sequenced. Sequence analyses and comparisons showed DNA-A of G16, G18, G32 and G63 shared more than 91.4% identity to each other, and they were most closely related with Tomato leaf curl Vietnam virus (ToLCVV) (82.8-86.4% sequence identity). According to geminivirus taxonomic criteria, these virus isolates were named as Tomato leaf curl China virus (ToLCCNV). DNAp was found to be associated with ToLCCNV. Analysis of DNAp molecules revealed that they are approximately half the size of the genomic DNA-A (1.3kb), and have little sequence homology to DNA-A of their cognate begomoviruses, except for the conserved TAATATTAC loop sequence. DNAp molecules contain a 115 nucleotides conserved region and an A-rich region with the length of about 230 nucleotides and have a common ORF encoding 119 amino acids on the complementary strand (designated Cl). Comparisons of DNAβ molecules of G16, G18 and G32 showed that G16p and G18P shared 93.1% identity to each other, while the sequence homology between G32p and G16P or G18P were 48.4-48.9%. G32pwas most closely related with Tomato yellow leaf curl China virus DNA p (89.2% sequence identity). So it is suggested that one virus probably can be associated with different DNA P molecules.Three full-length DNA-A molecules from tomato samples (G12, G22 and G30)were cloned and sequenced. Comparisons showed that G12, G22 and G30 were closely related to begomoviruses which were reported from Asia, and they are most closely related to that of Ageratum yellow vein China virus-[Hn2] (82.8-84.4% sequence identity). G12, G22 and G30 shared 92.7-95.9% identity to each other, indicating they are different isolates of one virus. According to geminivirus taxonomic criteria, G12, G22 and G30 are name as a distinct Begomovirus species, for which the name Papaya leaf curl China virus (PaLCuCNV) is proposed,.Virus isolates G13 was obtained from tomato plants. The complete DNA-A nucleotide sequences of G13 was determined. Sequence analyses and comparisons show that the DNA-A of G13 is most closely related with Ageratum yellow vein China virus-[Hn2] (90.7% sequence identity), so Gl3 is an isolate of AYVCNV.Virus isolate G35 was obtained from Euphorbia pulcherrima showing leaf curl symptoms. The virus was transmissible by whitefly to Nicoliana tabacum, Lycopersicon esculentum, Datura stramonium and Euphorbia pulcherrima. The complete nucleotide sequence of G35 was determined. Comparison showed the total DNA-A of isolate G35 was most closely related to that of Ageratum enation virus (79.9% sequence identity). However, the deduced coat protein of G35 is most like that of Pepper leaf curl virus from Bangladesh (94.9 % amino acid sequence identity), and the AC1 of G35 is most like that of Cotton leaf curl Multan virus-Okra (87.2% amino acid sequence identity). The molecular data showed that G35 is a distinct Begomovirus species, for which the name Euphorbia leaf curl virus (ELCV) is proposed.