Molecular Identification Of Geminiviruses Infecting Weeds In Guangxi

Geminiviruses are plant viruses characterized by their unique twinned particles, which encapsidate a circular single-stranded DNA genome. They have caused destructive diseases in many economically important crops throughout the world. In China, several kinds of begomoviruses were identified in tobacco, tomato and papaya in Yunnan and Guangxi provinces, and their genomic structure and variation were studied. Weeds are widely distributed in the world and have high environmental adaptability. Because weeds serve as important reservoir or alternate hosts for geminivirus, they seem to play an important role in disease spread, genomic variation and evolution of geminiviruses. In an attempt to know occurrence and distribution of geminiviruses infecting weeds, geminivirus samples were collected from weeds in Guangxi provinc and viruses were detected and identified with molecular technique.28 samples showing typical geminivirus symptoms were collected from 5 weed species. 22 samples were confirmed to be infected by geminiviruses with PCR detection using universal primer pair PA/PB for the genus Begomovirus. Comparisons of partial DNA-A sequences showed that these virus isolates could be classified into five groups. 8 representative isolates from each group were then chosen for complete DNA sequencing.The complete DNA-A sequences of isolates G37 and G38 from Ludwigia hyssopifolia were determined to be 2758 and 2745 nucleotides (nts), respectively. Sequence comparisons showed that DNA-A sequences of G37 and G38 had the highest sequence identity with that of Ageratum yellow vein Taiwan virus (AYVTV, 73%) and Ageratum yellow vein China virus (AYVCNV, 65%), respectively. The molecular data suggest that G37 and G38 are two distinct begomoviruses, for which the names Ludwigia yellow vein virus (LuYVV) for G37 and Ludwigia yellow vein China virus (LuYVCNV) for G38 are proposed. The satellite DNAβ molecule was only found to be associated with LuYVV using abutting primers betaOl and beta02 specific for DNAβ. The LuYVV DNAβ consists of 1347 nts, and shares relatively low nucleotide sequence identity (32.4% to 50.2%) with other previously characterized DNAβ molecules.The DNA-A sequences of isolates G47, G52 and G68 from Ageratum conyzoides were determined. Complete DNA-A sequences of isolates G52 and G68 are 2735 and 2740 nts, respectively. Partial DNA-A sequences of isolate G47 are 1743 nts. Sequence comparisons showed that DNA-A sequences of G47 and G68 had thehighest sequence identity with that of Papaya leaf curl China virus (PaLCCNV, 99%) and AYVCNV (98.1%), respectively, indicating that G47 is an isolate of PaLCCNV and G68 is an isolate of AYVCNV. G52 had the highest sequence identity with AYVCNV (85%), so it is a distinct begomovirus, for which the name Ageratum leaf curl virus (ALCV) is proposed. Genomic comparison also indicated that G52 had arisen by recombination among viruses related to AYVCNV, PaLCuCNV and an unidentified begomovirus. The mixed infections of AYVCNV and PaLCuCNV were existed in the field samples. DNAp molecules were only amplified from all the isolates of AYVCNV. The DNAp molecules associated with AYVCNV are 1315-1323 nts in size. Pairwise comparisons show that they are nearly identical and are most closely related to the DNAp associated with AYVV (78.4-80.5%).The complete DNA-A sequence of isolate G46 from Senecio scandens was determined to be 2746 nts, it shares the highest sequence identity with that of ALCV (72.4%), suggesting that G46 is a distinct Begomovirus species, for which the name Senecio yellow mosaic virus (SeYMV) is proposed. Phylogenetic analysis indicates that SeYMV may differ from other begomoviruses found in Asia for its evolutionary history.The complete DNA-A sequence of isolate G87 from Maluastrum coromandelianum was determined to be 2745 nts, it shares the highest sequence identity with that of Tobacco leaf curl Yunnan virus (TbLCYNV, 75.7%), suggesting that G87 is a distinct Begomovirus species, for which the name Maluastrum leaf curl virus (MLCV) is proposed. Defective DNAP molecule...