Genetic Diversity Of Rice Stripe Virus And Of Its Vector Laodelphax Striatellus

Rice stripe virus (RSV) is a planthopper-borne plant virus that causes serious damage to rice, which widely distributes in China. The genetic diversity of field populations of RSV and their planthopper vector Laodelphax striatellus were analyzed. RSV and L. striatellus populations were sampled from different locations in China, in areas where rice stripe disease occurs or does not occur.The 18S ribosomal RNA (rRNA) gene and the internal transcribed spacer 1 (1TS1) of small brown planthopper, L. striatellus, collected from 7 different geographic populations in China were analyzed by single-strand conformational polymorphism (SSCP) and sequence analysis. The result indicated they are all highly conserved within intraspecific taxa. The PCR products of two planthopper Nilaparvata lugens and Sogatella furcifera and one leafhopper Nephotettix cincticeps amplified with the same primer pairs showed that the 18S rRNA gene can not differentiate the four insects in length by gel electrophoresis, while the four ITS1 can distinguish from each other evidently. Furthermore, the sequences of 18S rRNA gene and 1TS1 sequences of I. striatellus were compared with the corresponding sequences in GenBank. The results showed neither the sequences of 18S rRNA gene nor ITS1 can be used for analysis of genetic diversity of L. striatellus, however ITS 1 sequences of L. striatellus can be used to derive a molecular phylogeny for the species and is suitable for species-level identification, while 18S rRNA gene sequences may prove useful for higher level phylogenetic analysis over a wide rang of taxa.Successful amplification of the intergenic spacer region (IGS) of the nuclear ribosomal repeat in L. striatellus was obtained with a PCR-based assay. The result showed that the IGS region sequences have 59%-60% AT content, which is much more than those of 18S rRNA gene but is slightly lower than those of ITS1. There are CAAT box and TATA box in IGS region deducing by software. Analyzing the IGS sequences from 7 regions in Yun-Nan and Jiang-su Province, the result indicated there is 9 sites change, in which there is a deletion site and 8 transition sites. These revealed a few within-species polymorphisms at the sequence level and there is no geographically difference.The random amplified polymorphic DNA (RAPD) optimal amplification condition for L. striatellus was determined by orthogonal test. At the same time, the effect of bovine serumalbumin (BSA) on RAPD was studied. The results showed BSA can affect the result of RAPD distinctly. Genetic diversity of I. striatellus collected from Baoshan, Dali, Chuxiong, Xishan, Kunming, in Yunnan province and Hongze, Nanjing, in Jiangsu province was estimated by RAPD. The result showed there are genetic variations among different L. striatellus populations, and the genetic distance is 0.15-0.30. The result also indicated the genetic distance between different populations is unrelated to the geographic distance between them distinctly.Variability of the Coat protein (CP) gene of RSV from 1998 to 2003 was assessed by sequence analysis. Sequence analysis of 43 isolates showed there is nucleotide diversity of CP gene in the field population, whether between different geographic location isolates, between different isolates in a given location or within a single given isolate. There are all base substations but not insert or deletion of bases in these variability. The value of genetic diversity is 0.03449. These isolates can be separated into two groups according to the sequence homology. Yunnan isolates are classified into one group, and the others are classified into another group in which the Japanese isolate can be separated singly. The result indicated there is a little relativity between the variability of RSV and the geographic location. The ratio between nonsynonymous and synonymous substitutions for CP gene is 0.092 which indicated the negative selective pressure for amino acid changes. No distinct correlation was found among isolates in different years or different isolates in one year in a...