| Malvastrum yellow vein virus?MaYVV?and Malvastrum yellow vein Yunnan virus?MaYVYV?belong to genus Begomovirus,which associated with betasatellite?MaYVB and MaYVYB?.They are two different pathogenic types of monopartite begomoviruses.Which are mainly co-infect weeds in the families Malvacea and Asteraceae,with other geminiviruses,but seldom reports on crops.In our laboratory,the genetic variation mechanism of the begomoviruses on crops was studied systematically.In order to further understand the genetic variation mechanism and evolutionary trajectory of the begomoviruses on crops and weeds.MaYVV and MaYVYV were used as the research object,the host range,distribution and genetic variation were studied.A total of 181 field samples of weeds and crops from Malvastrum conyzoides,Ageratum conyzoides,tomato,pepper and sweet potato were collected from Sichuan,Fujian,Guangxi,Guangdong and Yunnan province of China.The samples were detected by PCR using the universal primers for begomovirus and the associated betasatellite.Results showed that the detection ratio of begomovirus and betasatellite on weeds were 69.06% and 40.33% respectively.Begomoviruses were absent on crops.In the geminivirus and betasatellite detection was positive samples,specificity detection of MaYVV/MaYVB and MaYVYV/MaYVYB revealed detection ratio of 31.20% and 53.42%,41.60% and 61.64%,respectively.With detection ratio of co-infection was 32.26%.Results indicated that MaYVV and MaYVYV were prevalent on weeds,and especially frequently infect on Malvastrum conyzoides with the co-infection up to 31.18%,but were not detected on the crop.Compared with MaYVV,MaYVYV has a larger geographical distribution.Samples from different hosts and different regions were randomly selected for PCR amplification,cloning and sequencing.Three full length sequences of Ma YVV isolates were obtained from Sichuan Malvastrum conyzoides SC933,Guangxi Malvastrum conyzoides GX125 and GX175 and four full length sequences of MaYVYV isolates were obtained from Sichuan Malvastrum conyzoides SC933 and SC939,Guangxi Malvastrum conyzoides GX125 and GX199.Together with sequences downloaded from the GenBank,the genetic variation and evolution of MaYVV and MaYVYV the population was analyzed.The results showed that there were significant genetic differences among MaYVV isolates from different hosts and different years indicating that the genetic variation of MaYVV population was strongly influenced by geographical factors,host factors and time changes,while the genetic variation of MaYVYV population ws mainly affected by geographical factors.Neutral test revealed that the D valueof MaYVV population was positive to be 0.87616 1.13887,while that of MaYVYV population was negative to be-2.48095 -2.05184,with significant difference.These results indicated that MaYVVV population formed into a balanced or stable situation,while MaYVYV population is forming a trend of expansion.No intra-species recombination events were detected of MaYVV and MaYVYV.Genetic diversity analysis showed that the haplotype diversity?Hd?and nucleotide diversity?Pi?value of MaYVV population were 0.944 ± 0.070 and 0.02433 ± 0.00315,respectively,and the corresponding Hd and Pi values of MaYVYV population were 0.971 ± 0.033 and 0.00414 ± 0.00046,indicating that MaYVV and MaYVYV populations occupies a rich genetic diversity with weak selective pressure.The Pi value of the MaYVV and MaYVYV populations IR regions were 0.06467 ± 0.00912 and 0.00567 ± 0.00177,respectively,which were greater than those of AC1,AC4 and AV1.These results revealed that the genetic variation of the IR region of MaYVV and MaYVYV groups was the highest with a weak selection pressure.The AC1,AC4 and AV1 regions were conserved with a strong selection pressure.B60?60dpi?and B120?120dpi?populations were constructed by inoculating Nicotiana benthamiana with MaYVV infectious clone Y47A?Y47A?and its betasatellite?Y47??,respectively.At the same time,the natural populations of MaYVV?isolate SC906 and SC915?were constructed from Sichuan Malvastrum conyzoides samples and the natural populations of MaYVYV?isolate SC933,GX149 and GX1615?were established from Sichuan Malvastrum conyzoides,Guangxi Malvastrum conyzoides and Guangxi Ageratum conyzoides.Genetic structure and variation of MaYVV and MaYVYV experimental and natural populations were analyzed.The results showed that the genetic structures of experimental population and natural population of MaYVV,as well as the natural population of MaYVYV,are of the characteristics of "quasi-species".The percentage of mutant clones and mutation frequency of MaYVV experimental population B60 were 22.72% and 2.03×10-4,respectively.The percentage of mutant clones and mutation frequency of population B120 were 51.52% and 5.18×10-4,respectively,indicating that the genetic variation of MaYVV experimental population showed an upward trend with the passes by time.The mutation frequencies of SC906 and SC915 were 2.54×10-4 and 8.55×10-4,respectively,which were slightly higher than those of experimental populations,and the mutation frequencies of natural populations SC933,GX149 and GX199 of MaYVYV were 9.26×10-4,1.52×10-3 and 9.59×10-4,respectively,which were higher than those of MaYVV natural population.Further analysis showed that the non-coding region of each population had the most mutation in the IR region with the mutation frequency more than 10-3.For MaYVV experimental population,the mutation sites in the IR region were mainly concentrated in the 2635 st base?mainly transiation from G to A?at the 3'-end,while for MaYVYV natural population,the mutation sites in the IR region were mainly focus on the 2669 st base?mainly transition from C to T?at the 3'-end except for the population GX161.AC1 and AC4 overlap regions shared lower variation than those of AC1 non-overlapping regions,indicating unbalanced mutations coding regions of MaYVV and MaYVYV populations.The mutant types of the two viruses were mainly base C mutation to base T,with several base insertion and deletion. |
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