Molecular Identification Of Geminiviruses Infecting Weeds In Yunnan

Geminiviruses have been reported infecting tobacco, tomato and squash commonly and have caused significant yield losses in Yunnan Province. Geminiviruses is likely to be transmitted between weeds and crops, so research works were carried out to identify viruses in weeds in Yunnan.Thirty-nine geminiviruses samples were collected from Malvastrum coromandelianum, Ageratum conyzoides and Siegesbeckia orientalis plants in Yunnan. Partial sequences showed these samples were infected by different geminiviruses.Y160 was isolated from M. coromandelianum, complete DNA-A sequence ofY160 has the highest sequence identity (82.2%) with that of Malvastrum yellow veinvirus (AJ457824), so it is a distinct begomovirus, for which the name Malvastrumyellow vein Yunnan virus (MYVYNV) is proposed. A satellite DNA molecule wasfound to be associated with MYVYNV, it shares the highest nucleotide sequenceidentity (72.3%) with MYVV DNA β. Comparison with other begomoviruses showsthat MYVYNV has probably arisen from recombination of MYVV and Tomatoyellow leaf curl Thailand virus. Infectious clones of DNA-A and DNA β of Y160were constructed. Y160 DNA-A alone or together with DNAβ could systemicallyinfect Nicotiana benthamiana plants, DNAβ molecule is not necessary for symptominduction of Y160 DNA-A but can increase symptom. Furthermore, DNAβ canincrease DNA-A accumulation in plants.Twenty DNAβ molecules were isolated from M. coromandelianum in different regions of Yunnan. Comparisons of the nucleotide sequences indicate that all the 20 DNAβ molecules have the highest nucleotide sequence identities (93.2-97.3%) with MYVV DNAβ , indicating all these molecules are associated with MYVV. The sequences of 20 DNAβ molecules share 93.0-99.8% overall nucleotide sequence identities with each other, indicating that variations are relatively less among the 20 DNAβ molecules originated from different regions in Yunnan. The variations of DNAβ probably have some relationship with virus host range. Narrow host range of virus results in less variations of DNAβ .Mixed infections were tested with specific primers among 25 M. coromandelianum samples collected in Yunnan. The results showed that the mixed infections of MYVV and Tomato yellow leaf curl China virus (TYLCCNV) were found in 13 samples. The ratio of mixed infection is more than 52%, indicating that mixed infections of begomoviruses occur commonly in fields.DNA-A sequences of Y193 and Y194 originated from M. coromandelianumsamples were determined. Comparisons of nucleotide sequences indicate that Y193 DNA-A shares relatively high sequence identity (98.7%) with that of Y194, and both Y193 and Y194 have the highest nucleotide sequence identities (88.0%, 87.7%) with that of TYLCCNV-To[Y25]. Further sequence analysis indicates that Y193 and Y194 probably have arisen from recombination between TYLCCNV and another virus.The complete DNA-A sequences of Y206, Y282 and Y283 from A. conyzoides showing yellow vein symptoms were determined. Comparisons with other begomoviruses show that Y206 DNA-A is most closely related to that of MYVV with 95.1% nucleotide sequences identity, and its associated DNAβ shares the highest nucleotide sequence identity (92.8%) with MYVV DNA β. Y282 and Y283 DNA-A have the highest sequence identities with that of TbCSV-[Y35] and TbLCYNV-[Y161] (99.7% and 97.3%), respectively, indicating that Y206, Y282 and Y283 are isolates of MYVV, TbCSV and TbLCYNV, respectively.Six DNA β molecules associated with TYLCCNV were isolated from S. orientalis showing vein swelling symptoms. They could be divided into two groups according to their sequence identities. DNAβ molecules in the same group were originated from the same region, and they shared more than 98.2% nucleotide sequence identities with each other, whereas DNAβ molecules between the two groups had relatively lower sequence identities (75.4-75.8%) with each other. The variations of TYLCCNV DNAβ molecules from S. orientalis in same region are less, whereas the variations of TYLCCNV DNAβ molecules in different regions are more.