Molecular Variability Of Barley Yellow Dwarf Viruses

Barley yellow dwarf viruses (BYDVs) are members of the plant virus family Luteoviridae. They were phloem-limited and obligately transmitted in the circulative/persistent manner by several species of cereal aphids and can cause significant economic losses worldwide because of damage to barley, wheat, and oats. In China, BYDVs caused mainly yellow dwarf diseases of wheat throughout the northern and northwestern provinces. Crop losses of 20%-30% had been observed for many years in Shaanxi and Gansu provinces, the last serious epidemic happened in Shaanxi, Shanxi, Gansu, and Hebei provinces as well as Ningxia and the Inner Mongolian autonomous regions in 1998.Because of the different geogaraphy sources, the variability of BYDVs may exist The main objective of the experiments was to identify the molecular variability, strain type and phylogenetic relationship of different BYDVs CP genes using the materials of Chinese wheat isolates which were infected by virus.Two hundred and seventy-nine wheat samples showing barley yellow diseases were collected from wheat field representative of eighteen regions in China.Reverse transcription polymerase chain reaction (RT-PCR) and nucleic acid spot hybridization (NASH) were made using the RNA of samples to detect the CP gene. The results showed that two hundred and one samples had positive reaction which indicate special fragements and positive spots and BYDV-GAV hold the more large proportion and BYDV-PAV BYDV-GPV showed predominance in specific regions.BYDV-PAV occur in Weinan and Yangling regions mainly and the proportion has risen from 7% in 2004 to 29.41% in 2005 .GPV, existed as particular strain in China, had less infection and appears in Yuncheng,Shanxi Province mostly. We presume the proportion of GAV may drop and that of PAV would have ascending tendency according to the quantity of positive GAV and PAV samples.The product of RT-PCR were cloned and sequenced, the molecular variability of GAV,PAV and GPVwere analysised through the mulriple sequences alignments.Comparison of 26 nucletide sequences of BYDV-GAV revealed high conservation of the CP gene. Phylogenetic tree constructed based on the sequences of GAV CP genes from China with several parallel branches showed that there was no obvious clustering.BYDV-PAV was another case, 179 substitutions in 600 nt implied high variality, especially 3' terminal sequence.The phylogenetic tree constructed based on the sequences of BYDV-PAV CP genes from China formed four branches (A to D).The average similarity within A ,B,C,D group is 98.6%,97.8%,98.8% and 94.9%,respectively,furthermore,the degree of identity among them was 95.5%(A and B),91.5%(A and C),78.4% (A and D) ,90.5%(B and C),78.0% (B and D) ,79.4% (C and D).. A,B and C group were all belong to PAV-CN isolate,even from the same branch,the variability of sequences of three groups is obvious,which resulted in the diversity clusterings. BYDV-GPV comprised 606bp and the degree of identity among sequences is high.The approximately complete nucleotide sequence of genomic RNA of 05GG2, which was differ from other PAV samples was determined. It comprised 5675 nucleotides and contained six open reading frames and four un-translated regions. The size and organization of 05GG2 genome were similar to thoseof BYDV PAV-aus. The nucleotide and deduced amino acid sequences of the six ORFs were aligned and compared with those of other BYDV-PAV isolates. The results showed that there was a high degree of identity between 05GG2 and PAV-aus in all ORFs except ORFS and ORF6, which had only 88.7% and 81.7% identities respectively. The reported genomic nucleotide sequence of PAV-aus was longer than that of 05GG2, but the comparison of the genomic nucleotide sequences for PAV-aus and 05GG2 showed 93.6% sequence identity for the same region of the genome. According to the level of sequence similarities, 05GG2 should be closely related to BYDV-PAV-aus.