Rice Black-streaked Dwarf Disease Research Articles

Identification of the coexisting virus-derived siRNA in maize and rice infected by rice black-streaked dwarf virus.

Rice black-streaked dwarf virus is transmitted by small brown planthoppers, which causes maize rough dwarf disease and rice black-streaked dwarf disease. This virus leads to slow growth or death of the host plants. During the co-evolutionary arms race between viruses and plants, virus-derived small interfering RNAs challenge the plant's defense response and inhibit host immunity through the RNA silencing system. However, it is currently unknown if rice black-streaked dwarf virus can produce the same small interfering RNAs to mediate the RNA silencing in different infected species. In this study, four small RNA libraries and four degradome libraries were constructed by extracting total RNAs from the leaves of the maize (Zea mays) inbred line B73 and japonica rice (Oryza sativa) variety Nipponbare exposed to feeding by viruliferous and non-viruliferous small brown planthoppers. We analyzed the characteristics of small RNAs and explored virus-derived small interfering RNAs in small RNA libraries through high-throughput sequencing. On analyzing the characteristics of small RNA, we noted that the size distributions of small RNAs were mainly 24-nt (19.74%-62.00%), whereas those of virus-derived small interfering RNAs were mostly 21-nt (41.06%-41.87%) and 22-nt (39.72%-42.26%). The 5'-terminal nucleotides of virus-derived small interfering RNAs tended to be adenine or uracil. Exploring the distribution of virus-derived small interfering RNAs hot spots on the viral genome segments revealed that the frequency of hot spots in B73 was higher than those in Nipponbare. Meanwhile, hotspots in the S9 and S10 virus genome segments were distributed similarly in both hosts. In addition, the target genes of small RNA were explored by degradome sequencing. Analyses of the regulatory pathway of these target genes unveiled that viral infection affected the ribosome-related target genes in maize and target genes in metabolism and biosynthesis pathways in rice. Here, 562 and 703 virus-derived small interfering RNAs were separately obtained in maize and rice, and 73 virus-derived small interfering RNAs named as co-vsiRNAs were detected in both hosts. Stem-loop PCR and RT-qPCR confirmed that co-vsiRNA 3.1 and co-vsiRNA 3.5 derived from genome segment S3 simultaneously play a role in maize and rice and inhibited host gene expression. The study revealed that rice black-streaked dwarf virus can produce the same small interfering RNAs in different species and provides a new direction for developing the new antiviral strategies.

Molecular mapping of QTL for rice black-streaked dwarf disease resistance in rice (Oryza sativa L.)

AbstractRice black-streaked dwarf disease (RBSDD) is one of the most serious crop diseases in Asia, causing serious damage to rice production. Therefore, reducing the harmful effects of RBSDD is vital to the food security of China and other Asian countries. In this study, 248 rice varieties from different countries were screened for resistance to RBSDD, and 19 varieties with high resistance to RBSDD were found. Among them, H185, an indica variety, showed stable and high resistance to RBSDD. Using an F2:3 population of H185 and Wuyujing 3 (WYJ3, a highly susceptible japonica rice variety), three QTL conferring resistance to RBSDD, namely qRBSDD2, qRBSDD7, and qRBSDD11 were identified, and they explained 53.6% of the total phenotypic variation. Among them, qRBSDD2 and qRBSDD7, with LOD scores of 4.26 and 4.25, respectively, were repeatedly detected in artificial inoculation conditions, accounting for 28.0% and 29.8% of the total phenotypic variation, respectively. Resistant alleles of the two QTL were all derived from H185, and several BC5F2 lines possessing single or two QTL of qRBSDD2 and qRBSDD7 exhibited higher resistance for RBSDD. The QTL detected in our study open new possibilities for breeding rice cultivars with RBSDD resistance through resistance gene pyramiding.

Development of a Dot-Elisa Assay for Diagnosis of Southern Rice Black-Streaked Dwarf Disease in the Field

Outbreaks of the Southern rice black-streaked dwarf virus (SRBSDV) have caused significant losses in many rice-growing areas in Vietnam, especially in both North and Central Vietnam in recent years. To detect the virus, traditional reverse transcription polymerase chain reaction (RT-PCR) methodology and immunoassays are currently employed. RT-PCR is accurate but requires expensive chemicals and instruments, as well as complex procedures that limit its applicability for field tests. To develop a cheaper, simpler, and reliable SRBSDV diagnosis assay based on the dot-enzyme-linked immunosorbent assay (dot-ELISA) method, anti-SRBSDV polyclonal antibodies were produced by using the antigens derived from the P10 coat protein of SRBSDV, which was achieved from a previous study. The IgG antibody purified from the antiserum of recombinant P10-immunized mice by protein A-agarose affinity chromatography could specifically detect both the target protein and SRBSDV at a dilution of 1:100000. In the trial test of SRBSDV diagnosis, the dot-ELISA assay using the obtained anti-SRBSDV antibody showed an accuracy rate of 90.9% in comparison with the standard RT-PCR assay. These results are important premises for the large-scale application of dot-ELISA assay for SRBSDV diagnosis in order to protect rice crops against viral disease damage.

The Dark Septate Endophyte, Phialocephala fortinii J2PC4, Mitigates Southern Rice Black-Streaked Dwarf Disease and Impacts the Mortality of White Back Planthopper

Southern rice black-streaked dwarf disease (SRBSDD), caused by the southern rice black-streaked dwarf virus (SRBSDV) and transmitted by the white-backed planthopper (WBPH), is a severe disease responsible for significant yield losses in Southeast Asia, including China. The present study investigated utilization of dark septate endophyte (DSE) fungi against SRBSDD and WBPHas a new, effective approach for managing this disease. An isolate of the DSE fungus, Phialocephala fortinii J2PC4, was selected based on its effective symbiosis with rice. Phialocephala fortinii J2PC4 significantly promoted the growth of the rice, increasing plant height (14.8%), fresh weight (59.5%), and dry weight (60.5%) relative to the untreated control in growth-promotion experiments. In experiments assessing disease and pest suppression, growth of rice plants P. fortinii J2PC4 also promoted growth, increasing plant height(22.4%), fresh weight (74.0%), and dry mass (32.4%). Plants infested with WBPH for 48 hours exhibited a WBPH mortality rate of 8.2% in P. fortinii J2PC4 treated plants compared to 1.5% in the control plants. Disease incidence of SRBSDD in the plants treated with P. fortinii J2PC4 exhibited a 28.5% reduction in SRBSDD disease incidence compared to control plants. P. fortinii J2PC4 colonization of rice seedlings decreased the malondialdehyde (MDA) content, increased the superoxide dismutase (SOD) and peroxidase (POD) activity in rice leaves and induced the expression of the resistance-related genes, AOS, PR1a, and PR1b. In contrast POX1 and OsSAUR2 were down-regulated, relative to control plants. Larval production by WBPH in P. fortinii J2PC4 treated plants was also 24.7% lower than control plants in the pest resistance experiment. Our results provide new insights on use of the DSE fungus, P. fortinii J2PC4, as a biofertilizer and a biocontrol agent, which can potentially be applied as a new, safe and effective treatments for growth stimulation and disease and pest control in rice plants.

Genome Editing of Rice eIF4G Loci Confers Partial Resistance to Rice Black-Streaked Dwarf Virus.

Rice black-streaked dwarf disease, caused by rice black-streaked dwarf virus (RBSDV), is a serious constraint in Chinese rice production. Breeding disease-resistant varieties through multigene aggregation is considered an effective way to control diseases, but few disease-resistant resources have been characterized thus far. To develop novel resources for resistance to RBSDV through CRISPR/Cas9-mediated genome editing, a guide RNA sequence targeting exon 1 of eIF4G was designed and cloned into a binary vector, pHUE401. This recombinant vector was used to generate mutations in the rice cultivar Nipponbare via Agrobacterium-mediated transformation. This approach produced heritable homozygous mutations in the transgene-free T1 generation. Sequence analysis of the eIF4G target region from T1 transgenic plants identified 3 bp deletion mutants, and analysis of the predicted amino acid sequence identified one amino acid deletion in mutants that possess near full-length eIF4G. Furthermore, our data suggest that eIF4G may plays an important role in rice normal development, as there were no eIF4G knock-out homozygous mutants in T1 generation plants. When homozygous mutant lines were inoculated with RBSDV, they exhibited enhanced tolerance to virus infection, without visibly affecting plant growth and development. However, the eif4g mutant plants showed the same sensitivity to rice stripe virus (RSV) infection as wild-type plants. Notably, the wild-type and mutant N-termini of eIF4G interacted directly with RBSDV P8 in yeast and in planta. Additionally, compared to wild-type plants, the eIF4G transcript level was reduced twofold in the mutant plants. These results indicate that site-specific mutation of rice eIF4G successfully conferred partial resistance specific to RBSDV associated with less transcription of eIF4G in mutants. Therefore, this study demonstrates that the novel eIF4G alleles generated by CRISPR/Cas9 represent valuable disease-resistant resources that can be used to develop RBSDV-resistant varieties.

Genome-Wide Association Study on Resistance to Rice Black-Streaked Dwarf Disease Caused by Rice black-streaked dwarf virus.

Rice black-streaked dwarf disease caused by Rice black-streaked dwarf virus (RBSDV) is one of the most destructive viral diseases of rice. Thus, it is imperative that resistant rice germplasms are screened for novel RBSDV-resistant genes. RBSDV resistance of a diverse global collection comprising 1,953 rice accessions was evaluated under natural conditions across 3 years. The average disease incidences of the Xian/indica (XI) subgroup were significantly lower than those of the Geng/japonica (GJ) subgroup. Interestingly, most XI-1A accessions in the Xian subgroup were significantly more susceptible than XI-1B accessions, even though XI-1A and XI-1B have a close phylogenetic relationship. Four Xian accessions stably and highly resistant to RBSDV were consistently identified in 2 years. Ten genomic regions (GRs) with 147 single nucleotide polymorphisms associated with RBSDV resistance were detected by a single-locus genome-wide association study (GWAS), of which five were repeatedly identified in a multilocus GWAS. Two previously reported GRs, grRBSDV-6.1 and grRBSDV-6.3, which were repeatedly detected as stably and highly associated with RBSDV resistance, contained 17 and seven genes, respectively, with significant differences of resistance among haplotypes. Haplotype analyses of the candidate genes LOC_Os06g03150 in grRBSDV-6.1 and LOC_Os06g31190 in grRBSDV-6.3 suggested that the former gene is mainly associated with the differentiation of resistance within the Xian subgroup and the latter gene mainly explains the difference in the resistance between Xian and Geng. Another three novel resistance GRs (grRBSDV-1.1, grRBSDV-7.1, and grRBSDV-9.1) were identified. Our findings may enhance the application of disease-resistant rice germplasms for breeding RBSDV-resistant varieties.

Molecular characteristics of segment 5, a unique fragment encoding two partially overlapping ORFs in the genome of rice black-streaked dwarf virus.

Rice black-streaked dwarf virus (RBSDV), a ds-RNA virus in Fijivirus genus with family Reoviridae, which is transmitted by the small brown planthopper, is responsible for incidence of maize rough dwarf disease (MRDD) and rice black-streaked dwarf disease (RBSDD). To understand the variation and evolution of S5, a unique fragment in the genome of RBSDV which encodes two partially overlapping ORFs (ORF5-1 and ORF5-2), we analyzed 127 sequences from maize and rice exhibiting symptoms of dwarfism. The nucleotide diversity of both ORF5-1 (π = 0.039) and ORF5-2 (π = 0.027) was higher than that of the overlapping region (π = 0.011) (P < 0.05). ORF5-2 was under the greatest selection pressure based on codon bias analysis, and its activation was possibly influenced by the overlapping region. The recombinant fragments of three recombinant events (14NM23, 14BM20, and 14NM17) cross the overlapping region. Based on neighbor-joining tree analysis, the overlapping region could represent the evolutionary basis of the full-length S5, which was classified into three main groups. RBSDV populations were expanding and haplotype diversity resulted mainly from the overlapping region. The genetic differentiation of combinations (T127-B35, T127-J34, A58-B35, A58-J34, and B35-J34) reached significant or extremely significant levels. Gene flow was most frequent between subpopulations A58 and B35, with the smallest |Fst| (0.02930). We investigated interactions between 13 RBSDV proteins by two-hybrid screening assays and identified interactions between P5-1/P6, P6/P9-1, and P3/P6. We also observed self-interactive effects of P3, P6, P7-1, and P10. In short, we have proven that RBSDV populations were expanding and the overlapping region plays an important role in the genetic variation and evolution of RBSDV S5. Our results enable ongoing research into the evolutionary history of RBSDV-S5 with two partly overlapping ORFs.

Dynamic phytohormone profiling of rice upon rice black-streaked dwarf virus invasion

Rice black-streaked dwarf virus (RBSDV) is the causal agent of rice black-streaked dwarf disease, a serious constraint to rice production. A great deal of effort has been made to elucidate the transcriptome and proteome changes of rice upon virus inoculation. However, the relationship between RBSDV invasion and rice endogenous phytohormone profiling is largely unclear. Here, we surveyed the dynamic content profiling of endogenous phytohormones, which were severely disturbed by RBSDV invasion. The levels of abscisic acid (ABA) and cytokinins (CTKs) increased, while indole-3-acetic acid (IAA), gibberellins (GAs), jasmonic acid (JA), and salicylic acid (SA) decreased, accompanied by changes in the transcripts of genes participating in phytohormone metabolism and signalling pathways. Moreover, exogenously supplied GA3 could rescue the typical dwarfing symptom, and pre-application of SA largely decreased the occurrence of RBSDV disease in rice. The results partially suggest that RBSDV successfully invaded host rice by modulating the expression patterns of phytohormone metabolism to upset the balance of plant endogenous phytohormones.

Differences in Molecular Characteristics of Segment 8 in Rice black-streaked dwarf virus and Southern rice black-streaked dwarf virus.

Rice black-streaked dwarf virus (RBSDV) and Southern rice black-streaked dwarf virus (SRBSDV) cause maize rough dwarf disease (MRDD) and rice black-streaked dwarf disease (RBSDD) in China. RBSDV segment 8 (S8) contains the only deletion mutation in the genomes of these viruses, which are both members of the genus Fijivirus. To illuminate the molecular differences between the RBSDV and SRBSDV genomes and better understand the evolution of these viruses, and to determine which virus is specifically associated with MRDD and RBSDD in each region, S8 was analyzed in 66 virus isolates collected from 10 geographic locations in China and 14 S8 sequences obtained from the National Center for Biotechnology Information GenBank. Phylogenetic analysis showed that the pathogen associated with MRDD and RBSDD in the Yellow and Huai River valleys was RBSDV, whereas the pathogen associated with these diseases in Sanya was SRBSDV. Codon usage bias in S8 differed significantly between RBSDV and SRBSDV, as indicated by effective number of codons used by a gene (Nc) and GC values, Nc plots, and variation explained by the first axis in correspondence analysis. The nucleotide identities among these 66 RBSDV and SRBSDV isolates ranged from 66.2 to 68.2%, and were considerably lower than the nucleotide identities within RBSDV (from 94.1 to 99.9%) or SRBSDV (from 93.9 to 100%) isolates. Most S8 polymorphisms were identified in the region from 1,000 to 1,200 bp in RBSDV and in the region from 500 to 700 bp in SRBSDV. The difference in the lengths of RBSDV (1,936 bp) and SRBSDV (1,928 bp) was due to an 8-bp deletion in the 3'-untranslated region of SRBSDV. Six recombination events were detected in S8 in RBSDV and two recombination events were detected in S8 in SRBSDV. Recombination breakpoints were found within the region containing the deletion mutation in nine isolates. However, no recombination events were detected between RBSDV and SRBSDV. Both of these viruses were under negative and purifying selection, although the ratio of nonsynonymous mutations to synonymous mutations (Ka/Ks) for RBSDV S8 (0.0530) was not significantly lower than that of SRBSDV S8 (0.0823, P = 0.1550). We found that SRBSDV was more highly genetically differentiated (product of effective population size and the migration rate among populations < 1; values for the among-populations component of genetic variation or normalized variation > 0.33; and P values of the sequence statistic, the rank statistic, and the nearest-neighbor statistic < 0.01) than RBSDV. However, gene flow between RBSDV and SRBSDV was not frequent.

Rice black-streaked dwarf virus Genome in China: Diversification, Phylogeny, and Selection.

Rice black-streaked dwarf virus (RBSDV), a Fijivirus, causes maize rough dwarf disease and rice black-streaked dwarf disease in the summer maize-growing regions of the Yellow and Huai rivers, respectively, in China. Nevertheless, the diversification and selection of the entire genome from S1 to S10 have not been illuminated. Molecular variation, evolution, conserved regions, and other genomic properties were analyzed in 21 RBSDV isolates from maize (Zea mays L.) and rice (Oryza sativa) hosts sampled from nine geographic locations in China. Low codon adaptation index values ranging from 0.1878 to 0.2918 indicated a low degree of codon-usage bias and low potential expression for all 13 RBSDV open reading frames (ORFs). ORF9-2 showed a stronger effect of codon usage bias than did other ORFs, as the majority of points for this ORF lay close to the standard curve in the Nc plot (the effective number of codons [Nc] versus the frequency of G+C at synonymous third-base positions [GC3]). A 9-bp deletion mutation was detected in the RBSDV genome in the 3' UTR of S8. Nucleotide diversity analysis indicated that the structural proteins of RBSDV, such as S2 and S4, were all more conserved than nonstructural proteins such as S9. Nucleotide diversity (π) was highest among S9 sequences (0.0656), and was significantly higher than among S4 sequences (0.0225, P < 0.01). The number of conserved regions among the 10 segments varied substantially. The highest number of conserved regions (5) was found in S5, whereas no conserved regions were identified in S9. Nucleotide diversity and the number of conserved regions were independent of the lengths of segments. Nucleotide diversity was also not correlated with the number of conserved regions in segments. Ten recombination events in 21 isolates were found in seven segments with breakpoint positions in UTRs, intergenic spacer regions, and gene coding regions. The number of recombination events was also independent of the lengths of segments. RBSDV isolates from China could be phylogenetically classified into two groups using either 10 segment sequences or the concatenated sequence of S1 through S10, regardless of host or geographical location. The phylogenetic tree generated from pairwise nucleotide identities of individual RBSDV segments such as S9 and S3, with nucleotide identity values of 93.74% and 95.86%, respectively, is similar to the tree constructed from the concatenated sequences of the entire RBSDV genome. The 13 RBSDV ORFs were under negative and purifying selection (Ka/Ks < 1). ORF5-2 was under the greatest selection pressure; however, ORF2, which encodes the core protein of RBSDV, was under the lowest selection pressure.

Transcriptional changes of rice in response to rice black-streaked dwarf virus

Rice black-streaked dwarf virus (RBSDV), a member of the genus Fijivirus in the family Reoviridae, causes significant economic losses in rice production in China and many other Asian countries. Although a great deal of effort has been made to elucidate the interactions among the virus, insect vectors, host and environmental conditions, few RBSDV proteins involved in pathogenesis have been identified, and the biological basis of disease development in rice remains largely unknown. Transcriptomic information associated with the disease development in rice would be helpful to unravel the biological mechanism. To determine how the rice transcriptome changes in response to RBSDV infection, we carried out RNA-Seq to perform a genome-wide gene expression analysis of a susceptible rice cultivar KTWYJ3. The transcriptomes of RBSDV-infected samples were compared to those of RBSDV-free (healthy) at two time points (time points are represented by group I and II). The results derived from the differential expression analysis in RBSDV-infected libraries vs. healthy ones in group I revealed that 102 out of a total of 281 significant differentially expressed genes (DEGs) were up-regulated and 179 DEGs were down-regulated. Of the 2592 identified DEGs in group II, 1588 DEGs were up-regulated and 1004 DEGs were down-regulated. A total of 66 DEGs were commonly identified in both groups. Of these 66 DEGs, expression patterns for 36 DEGs were similar in both groups. Our analysis demonstrated that some genes related to disease defense and stress resistance were up-regulated while genes associated with chloroplast were down-regulated in response to RBSDV infection. In addition, some genes associated with plant-height were differentially expressed. This result indicates those genes might be involved in dwarf symptoms caused by RBSDV. Taken together, our results provide a genome-wide transcriptome analysis for rice plants in response to RBSDV infection which may contribute to the understanding of the regulatory mechanisms involved in rice-RBSDV interaction and the biological basis of rice black-streaked dwarf disease development in rice.

Mapping QTLs conferring resistance to rice black-streaked dwarf disease in rice (Oryza sativa L)

Rice black-streaked dwarf disease, caused by the rice black-streaked dwarf virus (RBSDV), can lead to severe yield losses in rice. The deployment of resistant cultivars is an effective disease control measure, but few studies related to the genetics and breeding of RBSDV resistance have been reported in rice. Here, we identified ‘IR36’ (indica) and ‘L5494’ (japonica) as resistant and susceptible parents, respectively, using a field test, and 208 recombinant inbred lines were derived from their cross. A genetic analysis indicated that the resistance of rice materials to RBSDV was controlled by quantitative trait loci (QTLs). A total of 12 QTLs for RBSDV resistance on chromosomes 1, 6, 8 and 9 were identified in three environments (2013–2015), and QTLs in two marker intervals, RM19234–CHR6-2 and RM3700–RM160 on chromosomes 6 and 9, respectively, were consistently detected. These QTLs explained 6.19–29.00 % of the total phenotypic variation for rice black-streaked dwarf disease incidence. The alleles enhancing resistance on chromosomes 6 and 8 originated from ‘IR36’, whereas the alleles on chromosomes 1 and 9 originated from ‘L5494’. The materials and identified resistance QTLs in this study are expected to be useful resources for efficiently breeding rice cultivars resistant to RBSDV.

Screening of rice (Oryza sativa) cultivars for resistance to rice black streaked dwarf virus using quantitative PCR and visual disease assessment

Rice black streaked dwarf virus (RBSDV) causing rice black streaked dwarf disease is transmitted by the small brown planthopper (SBPH, Laodelphax striatellus) in a persistent propagative manner. The disease is considered among the most destructive in rice production in east and southeast Asia. For sustainable control of the disease, planting resistant cultivars is the most economical and efficient method. The virus content in different rice cultivars was quantified using a TaqMan RT‐qPCR assay under greenhouse conditions and the disease was visually assessed in these cultivars in both greenhouse and field conditions. Results revealed significant positive moderate correlation (r = 0.3787; P = 0.0009) between the virus content and visual disease assessment in the greenhouse under forced inoculation. Among 66 rice cultivars, there was no significant difference in RBSDV genome equivalent copies (GEC) in seven cultivars, namely Lian‐dao 9805 (200.2 ± 12), Liangyou 3399 (206.6 ± 28), Ningjing 4 (206.6 ± 28), DaLiang 207 (302.0 ± 61), X 008 (354.0 ± 30), Shengdao 301 (658.4 ± 69) and Liangyou 1129 (679.5 ± 98). These cultivars were also visually assessed as resistant under greenhouse and field conditions. These cultivars could be used in disease management to reduce the likelihood of epidemics.

Molecular Genetic Analysis and Evolution of Segment 7 in Rice Black-Streaked Dwarf Virus in China.

Rice black-streaked dwarf virus (RBSDV) causes maize rough dwarf disease or rice black-streaked dwarf disease and can lead to severe yield losses in maize and rice. To analyse RBSDV evolution, codon usage bias and genetic structure were investigated in 111 maize and rice RBSDV isolates from eight geographic locations in 2013 and 2014. The linear dsRNA S7 is A+U rich, with overall codon usage biased toward codons ending with A (A3s, S7-1: 32.64%, S7-2: 29.95%) or U (U3s, S7-1: 44.18%, S7-2: 46.06%). Effective number of codons (Nc) values of 45.63 in S7-1 (the first open reading frame of S7) and 39.96 in S7-2 (the second open reading frame of S7) indicate low degrees of RBSDV-S7 codon usage bias, likely driven by mutational bias regardless of year, host, or geographical origin. Twelve optimal codons were detected in S7. The nucleotide diversity (π) of S7 sequences in 2013 isolates (0.0307) was significantly higher than in 2014 isolates (0.0244, P = 0.0226). The nucleotide diversity (π) of S7 sequences in isolates from Jinan (0.0391) was higher than that from the other seven locations (P < 0.01). Only one S7 recombinant was detected in Baoding. RBSDV isolates could be phylogenetically classified into two groups according to S7 sequences, and further classified into two subgroups. S7-1 and S7-2 were under negative and purifying selection, with respective Ka/Ks ratios of 0.0179 and 0.0537. These RBSDV populations were expanding (P < 0.01) as indicated by negative values for Tajima's D, Fu and Li's D, and Fu and Li's F. Genetic differentiation was detected in six RBSDV subpopulations (P < 0.05). Absolute Fst (0.0790) and Nm (65.12) between 2013 and 2014, absolute Fst (0.1720) and Nm (38.49) between maize and rice, and absolute Fst values of 0.0085-0.3069 and Nm values of 0.56-29.61 among these eight geographic locations revealed frequent gene flow between subpopulations. Gene flow between 2013 and 2014 was the most frequent.

Phylogenetic and recombination analysis of rice black-streaked dwarf virus segment 9 in China.

Rice black-streaked dwarf virus (RBSDV) is an economically important virus that causes maize rough dwarf disease and rice black-streaked dwarf disease in East Asia. To study RBSDV variation and recombination, we examined the segment 9 (S9) sequences of 49 RBSDV isolates from maize and rice in China. Three S9 recombinants were detected in Baoding, Jinan, and Jining, China. Phylogenetic analysis showed that Chinese RBSDV isolates could be classified into two groups based on their S9 sequences, regardless of host or geographical origin. Further analysis suggested that S9 has undergone negative and purifying selection.

Detection, Occurrence, and Survey of Rice Stripe and Black-Streaked Dwarf Diseases in Zhejiang Province, China

The major viral diseases that occur on rice plants in Zhejiang Province, eastern China, are stripe and rice black-streaked dwarf diseases. Rice stripe disease is only caused by rice stripe tenuivirus (RSV), while rice black-streaked dwarf disease can be caused by rice black-streaked dwarf fijivirus (RBSDV) and/or southern rice black-streaked dwarf fijivirus (SRBSDV). Here we review the characterization of these viruses, methods for their detection, and extensive surveys showing their occurrence and spread in the province.

The Efficiency of Southern rice black-streaked dwarf virus Transmission by the Vector Sogatella furcifera to Different Host Plant Species

Southern rice black-streaked dwarf disease is a new rice disease that severely affects rice production in South China. To understand transmission capacity of the vector Sogatella furcifera to Southern rice black-streaked dwarf virus (SRBSDV) among different host plant species, potential host plants of SRBSDV collected from the diseased rice field and/or adjacent to the field in Hunan Province, China, were determined by RT-PCR, and the transmission rates of SRBSDV by S. furcifera among different host plant species were investigated. The results showed that host plants of SRBSDV in the rice fields were five of family Gramineae (Oryza sativa, Echinochloa crusgalli, Zea mays, Paspalum distichum, Alopecurus aequali) and two of family Cyperaceae (Juncellus serotinus and Cyperus difformis). S. furcifera could not transmit SRBSDV between gramineous plants and cyperaceous plants, and could not transmit SRBSDV between the gramineous plants, J. serotinus and C. difformis as well. However, SRBSDV could be transmitted by S. furcifera within gramineous plants. S. furcifera could transmit SRBSDV between interspecies among three species plants (O. sativa, E. crusgalli and Z. mays), and between P. distichum and A. aequali. At 15, 20, 25, 30, and 35°C, both macropterous and brachypterous adult of S. furcifera could transmit SRBSDV from the plants (e.g., E. crusgalli, Z. mays and O. sativa) infected with SRBSDV to rice seedlings. The transmission rates were first increased and then decreased with the increase of temperature. Macropterous adults transmitted SRBSDV from the viruliferous E. crusgalli, Z. may and rice plants to the healthy rice seedlings, and the infected rates of rice seedlings were 26.2, 18.8 and 23.7% at 15°C, 56.6, 64.6 and 53.6% at 25°C, and was 11.2, 10.2 and 7.3% at 35°C, respectively. Transmission capacity of brachypterous adults was significantly higher than that of macropterous adults at 15, 20 and 25°C (P<0.05), while transmission capacity of brachypterous adults was relatively lower compared with that of macropterous ones at 35°C. These results offer evidence on the transmission of SRBSDV via the vector S. furcifer among different host plants, which can be helpful to control Southern rice black-streaked dwarf disease by the appropriate cultural measures in South China.

Transmission of Rice Black-Streaked Dwarf Virus from Frozen Infected Leaves to Healthy Rice Plants by Small Brown Planthopper ( Laodelphax striatellus)

In order to preserve virus for identifying the resistance of rice varieties against rice black-streaked dwarf disease, a simple and reliable method was developed, through which virus-free small brown planthopper (SBPH) acquired rice black-streaked dwarf virus (RBSDV) from frozen infected leaves and the virus was transmitted to healthy rice plants. The experimental results showed that SBPH could obtain RBSDV from frozen infected rice leaves and the virus could be transmitted to a susceptible rice variety. For the ability to acquire RBSDV and transmit the virus to healthy plants by SBPH, there was no significant difference between frozen infected leaves and in vitro infected leaves. The novel method could be applied to identification of rice variety resistance to rice black-streaked dwarf disease, facilitating the breeding process for rice black-streaked dwarf disease resistance.

Influence of different period transplanting on the occurrence of rice black-streaked dwarf disease

Influence of different period transplanting on the occurrence of rice black-streaked dwarf disease

Infection period of rice black-streaked dwarf disease

Infection period of rice black-streaked dwarf disease