Molecular Identification Of Geminiviruses Infecting Siegesbeckia Orientalis L. And Malvastrum Coromandelianum

Twenty-three virus samples were collected from Siegesbeckia orientalis, Malvastrum coromandelianum, Ageratum conyzoides, Amaranthus spp, Parthenium spp and Artemisia spp, and these samples were tested by TAS-ELISA with monoclonal antibodies (MAb) against begomoviruses. Detection results showed samples VA2, VA7 and VA8 from Malvastrum coromandelianum had weak reaction with MAb SCR18, and samples X2 from Siegesbeckia orientalis had weak reaction with MAb SCR18 and SCR106, while other samples had no reaction with MAbs. A specific band about 500 bp was amplified from samples VA2, VA7, VA8 and X2 with degenerate primers PA and PB. Sequence analysis of PCR products showed DNA fragments from VA2, VA7, VA8 have more than 95% sequence homology each other, while only 80% sequence homology were found when compared with DNA fragment from X2. The result shows that virus isolates from VA2, VA7, VA8 belong to one virus, while virus isolate from X2 belong to another virus.The complete nucleotide sequence of X2 DNA-A was determined, it contains 2730 nucleotides, having typical genomic organization of a begomovirus, encoding six ORFs with two ORFs [AVl(CP) and AV2] in virion-sense DNA and four ORFs (AC1-AC4) in complementary-sense DNA. Similarity searches showed that X2 DNA-A has the highest sequence identity (99%) with that of Tomato yellow leaf curl China virus (TYLCCNV) isolate Y38. So, it is concluded that X2 infecting Siegesbeckia orientalis is an isolate of TYLCCNV.The complete nucleotide sequence of VA2 DNA-A was determined, it contains 2731 nucleotides, having typical genomic organization of a begomovirus, encoding six ORFs with two ORFs [AVl(CP) and AV2] in virion-sense DNA and four ORFs (AC1-AC4) in complementary-sense DNA. Similarity searches showed that VA2 DNA-A has the highest sequence identity (77%) with that of Okra yellow vein mosaic virus-[201], while less than 76% identities are found when compared with other begomoviruses. In general, overall nucleotide sequence identity between two distinct viruses are less than 89%, and strains of virus must have sequence identity greater than 89%, so VA2 is a distinct begomoviruses. In accordance with the revised proposal for naming geminiviruses, we propose to name VA2 as Malvastrum yellow vein virus (MYVV).