Study On Geminiviruses Infecting Carica Papaya And Ageratum Conyzoides

Leaf curl symptom of papaya (Carica papaya) occurred severely in recent years in south-west part of China. The papaya leaf curl samples from Guangxi and Guangdong provinces were collected and studied, and ageratum yellow vein sampleswere also collected and studied.7 papaya leaf curl samples collected from Guangxi province and 1 fromGuangdong province, and 5 ageratum yellow vein samples from Guangxi province were tested with triple antibody sandwich ELISA (TAS-ELISA) and PCR, Results showed all the virus samples were infected by whitefly-transmitted geminiviruses. The products of PCR were cloned and sequenced. Sequence analyses showed 2 types of viruses existed among those samples, a few samples were infected by several geminiviruses.The full-length DNA-A molecules from papaya sample G2 and GD2 were cloned and sequenced. Sequence analyses and comparisons showed that DNA-A between G2 and GD2 shared only 73.4% nucleotide sequence identity. So G2 and GD2 were 2 different begomovirus species. Sequence comparisons and phylogenetic analysis showed that DNA-A of G2 was most related to that of Ageratum yellow vein China virus-[Hn2] (AYVCNV-[Hn2] with 83.4% nucleotide sequence identity, and GD2 were most related to that of Ageratum yellow vein virus (AYVV) , with 75.2% nucleotide sequence identity. According to geminivirus taxonomic criteria, the name Papaya leaf curl China virus (PaLGuCNV) for G2 and Papaya leaf curl Guangdong virus (PaLCuGV) for GD2 were proposed, and the two viruses were approved by International Committee on Virus Taxonomy. Compared with deduced ORFs showed the coat protein of G2 and GD2 shared highest amino acid sequence similarity (97.7% and 94.2% respectively) with that of Pepper leaf curl virus-[Malaysia] (PepLCV-[MY]), suggesting that CP of these three isolates may evolved from identical ancestor.The full-length DNA-A molecules from ageratum sample G8 and G10 were cloned and sequenced. Sequence analyses and comparisons showed DNA-A of G8and G10 shared 93.2% identity to each other, So G8 and G10 were isolates of a same begomovirus. Comparisons with other geminiviruses showed that the DNA-A of G8 and G10 were most closely related to that of PaLCuCNV-[G2] (92% and 89.2% sequence identity, respectively), so G8 and G10 were regarded as virus isolates of PaLCuCNV. Comparisons with encoded amino acid sequences of CP show that G8 and G10 may have a common ancestor with PepLCV-[MY] (98.4% sequence identity), and the amino acid sequences of AC 1 (rep) AC2, AC3 AC4 of G8 and G10 had highest identities with that of AYVCNV, indicated that they may have evolved from the same ancestry. The molecular data showed that G8 and G10 might be a recombination Begomovirus species.Mixed infection was tested in G7 with primers specific for DNA-A of several geminiviruses. The results showed that mixed infection of begomo viruses occurred in G7. Partial DNA-A sequence comparison with other geminiviruses showed that G7 were infected with 5 begomoviruses, these viruses were Papaya leaf curl China virus, Ageratum yellow vein china virus, Tomato leaf curl China virus, Euphorbia leaf curl virus and Tobacco leaf curl Yunnan virus.