The Distribution And Genetic Diversity Of Rice Black Streaked Dwarf Virus And Southern Rice Black Streaked Dwarf Virus In China

Rice black-streaked dwarf virus (RBSDV) and Southern rice black-streaked dwarf virus (SRBSDV) are recently two major virus causing extensive rice and maize losses in China. To determination their geographic distribution in China, we detected1524plant samples acquired from161counties of17provinces during the2009and2010growing seasons using reverse-transcription polymerase chain reaction (RT-PCR). Of which1414samples relating to313rice varieties were collected from rice fields, while others from maize fields. We found that21.33%samples were infected by RBSDV, and another55.97%infected by SRBSDV. RBSDV distribute mainly in Shanghai, Jiangsu, Shandong, Hebei, Zhejiang, Anhui, and Jiangxi province, causing maize rough dwarf disease and rice black streaked dwarf disease, especially in Jiangsu province. SRBSDV was detected in115counties of13provinces, and widely distribution in southern China where hybrid rice was cultivated extensively. SRBSDV was more widespread in the areas where the interval between rice sowing and the main immigration period of white-backed planthopper was about one month, or where cropping patterns was diversity. These two viruses could infect different rice varieties including japonica rice, glutinous rice, indica rice and hybrid rice. Until now it has not found any varieties surveyed being resistance to RBSDV or SRBSDV.At the basis of determination the distribution of RBSDV in China, we studied the genetic diversity of RBSDV isolates from different locations by nucleotide sequencing comprising CP, S7-ORF1and S5-ORF2. The value of genetic diversity of CP was0.0400, phylogenetic analyses showed all isolates could be divided into two clear grouping; the value of genetic diversity of S7-ORF1was0.0179, it also can be divided into two groups, but most of isolates are clustered in one group which shared more than98%nucleotide and amino acid identity with Chinese isolates while several isolates shared94.3～99.0%nucleotide identity and98.5～100% amino acid identity with Japanese isolate; the value of genetic diversity of S5-ORF2was0.0285, all isolates are divided into two groups. Most of isolates from north of China were clustered into one group and most of isolates from sites located in south of China was clustered into another group. Different segments from single isolate also clustered into different groups and had distinctive genetic diversity. From the value of genetic diversity we concluded that partial sequence of S7-ORF1was the most conserved compared to S5-ORF2and CP, and CP was the most variable among three segments. The selective pressure estimated by ω (0.0488for CP,0.4278for S5-ORF2,0.0394for S7-ORF1) implied that three segments were under strong negative selection and S5-ORF2was slightly higher than that for two other segments and partial sequence of S7-ORF1under stricter selective constraints. The conservation of partial sequence of S7-ORF1may be corresponding with the function of its coding protein.We also analyzed the genetic variation of SRBSDV isolates from13provinces by nucleotide sequencing comprising partial sequence of S10-ORF and S7-ORF1. Comparison of the sequence of these two segments of all Chinese isolates with other isolates from Vietnam demonstrated that all SRBSDV isolates had little molecular variation, two segments shared more than97%sequence identities at nucleotide and amino acid levels, respectively, and little variation was found between isolates from different geographical origins and hosts. From the value of genetic diversity and ω of S10-ORF(0.0131,0.3162) and S7-ORF1(0.0053,0.1119). we concluded that S10-ORF was more variable than S7-ORF1and was under less selective pressure. In all, as an intrinsic virus, RBSDV has higher genetic diversity level than SRBSDV which is a new introduction virus and may derive from a single origin.