Genotype Analysis And Activation Of Endogenous Banana Streak Virus(eBSV)

Banana is an important fruits. Most bananas originated from M. acuminata(AA) and M. balbisiana(BB). The main types of banana in China are Cavendish(AAA), Plantain(ABB) and Pisang Awak subgroup(ABB). Banana streak virus(BSV) is a serious threat to banana production and germplasm exchange in recent years. A Banana streak virus(DQ451009) has been isolated from a diseased banana accession Baxijiao in Guangdong, The BSV was a variant of BSOLV and therefore named as BSOLV-GD(Banana streak OL virus Guangdong) according to virus taxonomy. Highly homologous sequences with BSV were found in the genome of banana, these sequences were called banana endogenous BSV(eBSV), the BSV which is independent on the chromosome of banana was called episomal BSV. The described eBSV have a similar rearranged pattern with tandem repeats, internal duplications, fragmentations and inversion of the viral genome. e BSV have different genotypes which could be divided into infected and non-infected type, The infection type could be activated to produce episomal virus which caused the occurrence of banana streak disease. In order to study the activation and its mechanism of eBSV of different genotypes, the primers were designed according to the structure of eBSOLV-GD to analyze the genotypes,expression and activation of e BSOLV-GD. The results were as follows:1. Multiplex direct binding PCR(M-DB-PCR) was used to detect episomal BSV in 23 banana accessions. All the banana accessions except Yunnanhuafen and No.1Zafen did not infected by BSOLV-GD. The non-infected banana accessions will be selected to study the activation of eBSV.2. A banana bacterial artificial chromosome(BAC) clones(AP009334) was found to contain 9 highly homologous sequences to the BSOLV-GD genome sequence after BLAST search. The structure map of eBSOLV-GD was made. Sequence analysis of base substitution between eBSOLV-GD in the BAC and BSOLV-GD, 50 mutations, in which 21 were synonymous mutations and 24 were non-synonymous mutations.3. In order to study the different genotypes of eBSV, the primers were designed according to the structure of eBSOLV-GD to analyze the e BSOLV-GD genotypes of 23 banana accessions. The results showed that the banana that contains only A genome did not contain eBSOLV-GD; There are seven eBSOLV-GD genotypes, some of which are infectious, in tested banana accessions which contain B genome.4. RT-PCR was used to study the eBSOLV-GD expression. The results showed that the internal fragments II and III in eBSOLV-GD of Plantain and Pisang Awak subgroup could be expressed, and the expression in Pisang Awak of eBSOLV-GD is the strongest among the 3 subgroups of banana and was about three times that of of plantains and cavendishe.5 genotypes of eBSOLV-GD without episomal BSOLV-GD were used to investigate the incidence of banana streak virus disease after tissue culture. The incidences of No.1 Guangfen-1 and Gaobafenjiao which were significantly higher than those of Cavendish and Plantain were 18.0% and 16.8%, respectively. There were no significant differences of the incidences between Cavendish and Plantain. The incidences were not related with eBSOLV-GD genotypes but related with subgroups of banana. The BSOLV-GD was found in diseased Plantain and Pisang Awak subgroups but not in diseased Cavendish subgroup using the method of M-DB-PCR. The BSV diseases in Plantain and Pisang Awak subgroups were caused by BSOLV-GD which was from the activation of eBSOLV-GD.