Viral Diseases Of Rice Research Articles

Transgenic Rice Plants Expressing Artificial miRNA Targeting the Rice Stripe Virus MP Gene Are Highly Resistant to the Virus

Simple SummaryRice stripe virus is a disastrous viral disease that causes significant yield losses in rice production in South, Southeast, and East Asian countries. To decrease the use of chemical insecticides, genetic engineering has become a pivotal strategy to combat the virus. In this study, we constructed a dimeric artificial microRNA precursor expression vector that targets the viral MP gene based on the structure of the rice osa-MIR528 precursor. Marker-free transgenic plants successfully expressing the MP amiRNAs were obtained and were highly resistant to RSV infection. The novel rice germplasms generated are promising for RSV control.Rice stripe virus (RSV) causes one of the most serious viral diseases of rice. RNA interference is one of the most efficient ways to control viral disease. In this study, we constructed an amiRNA targeting the RSV MP gene (amiR MP) based on the backbone sequence of the osa-MIR528 precursor, and obtained marker-free transgenic rice plants constitutively expressing amiR MP by Agrobacterium tumefaciens-mediated transformation. A transient expression assay demonstrated that dimeric amiR MP could be effectively recognized and cleaved at the target MP gene in plants. Northern blot of miRNA indicated that amiR MP-mediated viral resistance could be stably inherited. The transgenic rice plants were highly resistant to RSV (73–90%). Our research provides novel rice germplasm for RSV control.

Serological, molecular and phylogenetic analysis of Rice Yellow Mottle Virus (RYMV) isolates collected in Southern-Benin

The rice yellow mottle is the best known viral disease of rice in Africa. It causes significant economic losses in farmer’s fields. The serological properties of Rice Yellow Mottle Virus (RYMV) isolates, collected in Southern Benin, were assessed by immunological tests with polyclonal and monoclonal antibodies (Pabs and MAbs). The isolates CP (Capsid protein) portions, obtained by RT-PCR, were sequenced and their amino-acids sequences were analyzed and used for phylogenetic analysis. Three different RYMV pathogenic groups, including three resistance breaking (RB) isolates (Be20, Be21 and Be27) which over came allele rymv1-5gene, were identified. Two serotypes Ser1/strain S1 and Ser2/ strain S2 were also distinguished. The molecular properties of the isolates CP gene and the phylogenetic characteristics indicated that the Southern Benin RYMV strain is heterogeneous. The strain S1-Benin linked to the West Central African lineage(S1-WCA) is related to strain from Togo and Niger, whereas, the strain S2 Benin is the stumps of the West African lineage (S1-WA) and is related to Mali, Burkina Faso and Ivory Coast RYMV strains. These results reported the virus pathogenicity level and showed the relationships between RYMV strains in all Dahomey gap countries and in West and Central Africa. Keywords: serotypes, RYMV strains, RB isolates and phylogenetic analysis

Viral Diseases of Crops in Nepal

Viral diseases are the important diseases next to the fungal and bacterial in Nepal. The increase in incidence and severity of viral diseases and emergence of new viral diseases causes the significant yield losses of different crops in Nepal. But the research and studies on plant viral diseases are limited. Most of the studies were focused in viral diseases of rice (Rice tungro virus and Rice dwarf virus), tomato (Yellow leaf curl virus) and potato (PVX and PVY). Maize leaf fleck virus and mosaic caused by Maize mosaic virus were recorded as minor disease of maize. Citrus Tristeza Virus is an important virus of citrus fruit in Nepal while Papaya ringspot potyvirus, Ageratum yellow vein virus (AYVV), Tomato leaf curlJava betasatellite and Sida yellow vein Chinaalphasatellite were recorded from the papaya fruit. The Cucumber mosaic virus (CMV) and Zucchini yellow mosaic potyvirus (ZYMV) are the viral diseases of cucurbitaceous crop reported in Nepal. Mungbean yellow mosaic India virus (MYMIV) found to infect the many crops Limabean, Kidney bean, blackgram and Mungbean. Bean common mosaic necrosis virus in sweet bean, Pea leaf distortion virus (PLDV), Cowpea aphid‐borne mosaic potyvirus (CABMV), Peanut bud necrosis virus (PBNV) in groundnut, Cucumber mosaic virus (CMV). Chili veinal mottle potyvirus (CVMV) and Tomatoyellow leaf curl gemini virus (TYLCV) were only reported and no any further works have been carried out. The 3 virus diseases Soyabean mosaic (SMV), Soybean yellow mosaic virus and Bud blight tobacco ring spot virus (TRSV) were found in soybean.Int. J. Appl. Sci. Biotechnol. Vol 6(2): 75-80

Interaction between southern rice black-streaked dwarf virus minor core protein P8 and a rice zinc finger transcription factor.

The fijivirus southern rice black-streaked dwarf virus (SRBSDV) causes one of the most serious viral diseases of rice in China and Vietnam. To better understand the molecular basis of SRBSDV infection, a yeast two-hybrid screen of a rice cDNA library was carried out using P8, a minor core protein of SRBSDV, as the bait. A rice Cys2His2-type zinc finger protein (OsZFP) was found to interact with SRBSDV P8. A strong interaction between SRBSDV P8 and OsZFP was then confirmed by pull-down assays, and bimolecular fluorescence complementation assays showed that the in vivo interaction was specifically localized in the nucleus of plant cells. Using a series of deletion mutants, it was shown that both the NTP-binding region of P8 and the first two zinc fingers of OsZFP were crucial for their interaction in plant cells. The localization in the nucleus and activation of transcription in yeast supports the notion that OsZFP is a transcription factor. SRBSDV P8 may play an important role in fijiviral infection and symptom development by interfering with the host transcription activity of OsZFP.

Seasonal Changes in the Percentage of Rice Stripe Virus ViruliferousLaodelphax striatellus(Hemiptera: Delphacidae) in Paddy Fields in Japan

Rice stripe disease, which is caused by Rice stripe virus (RSV), is one of the most serious viral diseases of rice. RSV is transmitted in a persistent manner by Laodelphax striatellus (Fallén). The incidence of the disease can be estimated from the density of viruliferous vectors. Understanding seasonal changes of the percentage of viruliferous L. striatellus can facilitate forecasting and controlling the disease. In paddies, the percentage of viruliferous insects fluctuated in phase with the rate of detection of RSV-infected rice; it gradually increased from July to August, plateaued or temporarily declined in September, and increased sharply on ratoons in October. These findings indicate that horizontal transmission of RSV from diseased plants to vector insects occurred frequently, and the insects acquired RSV from the ratoons. However, the percentages of viruliferous insects overwintering in poaceous weeds, the main hosts for L. striatellus in winter, were lower than those in ratoons. Few L. striatellus that acquired RSV from ratoons seemed to move to overwintering sites and transmit the virus to the next generation. However, there was a tendency for the percentages of viruliferous overwintering insects to be higher on paddy ridges than in river levees. Insects could probably move from ratoons to poaceous weeds when the weeds were near a paddy. Although increasing percentage of viruliferous insects on ratoons seem to have relatively little impact on RSV dynamics in the next crop season, appropriate weed management around paddies is still needed to reduce the incidence of rice stripe disease.

The Differential Reaction of Rice Hybrids to Tungro Virus by Phenotyping and PCR Analysis

AbstractTwenty popular rice hybrids were used to screen for rice tungro virus (RTV) disease reaction. Virulent green leafhoppers (GLH) were used as vector to introduce RTV to the rice hybrids. Virus symptoms scores were recorded at 14, 21, 34, 41 and 59 days postinoculation (DPI), which suggested that virus symptoms are greatly influenced by growth stage of plants. To confirm the presence of virus, polymerase chain reaction (PCR)‐based detection of Rice tungro bacilliform virus (RTBV) was carried out at 7, 14, 21 and 59 DPI using virus genome‐specific primers. Virus presence was observed in all the rice hybrids and check varieties, particularly at later stages of infection. This study shows that phenotyping for tungro virus resistance in rice hybrids at 21 DPI gives most reliable results based on both virus symptoms and presence of virus. Further, to assess the relative difference in population of RTBV, quantitative PCR was performed in all the genotypes at 21 DPI. Yield data were also recorded from control and virus‐infected plants to estimate yield loss percentage due to tungro disease. This study is important to understand the response of rice hybrids to tungro virus disease. Results obtained in this study emphasize that molecular detection of virus is very important to screen the rice plants accurately for tungro disease reaction.

STV11 encodes a sulphotransferase and confers durable resistance to rice stripe virus.

Rice stripe virus (RSV) causes one of the most serious viral diseases of rice (Oryza sativa L.), but the molecular basis of RSV resistance has remained elusive. Here we show that the resistant allele of rice STV11 (STV11-R) encodes a sulfotransferase (OsSOT1) catalysing the conversion of salicylic acid (SA) into sulphonated SA (SSA), whereas the gene product encoded by the susceptible allele STV11-S loses this activity. Sequence analyses suggest that the STV11-R and STV11-S alleles were predifferentiated in different geographic populations of wild rice, Oryza rufipogon, and remained prevalent in cultivated indica and japonica rice varieties, respectively. Introgression of the STV11-R allele into susceptible cultivars or heterologous transfer of STV11-R into tobacco plants confers effective resistance against RSV. Our results shed new insights into plant viral defense mechanisms and suggest effective means of breeding RSV-resistant crops using molecular marker-assisted selection or genetic engineering.

Dynamics of Southern rice black-streaked dwarf virus in Rice and Implication for Virus Acquisition

A novel viral disease of rice caused by Southern rice black-streaked dwarf virus (SRBSDV) has spread throughout East and Southeast Asia since the mid-2000s. Outbreaks of this viral disease occur yearly in southern parts of Japan concurrently with overseas migration of the planthopper vector Sogatella furcifera from southern China during the rainy season (from late June to early July). We examined the dynamics (changes in titer and localization) of SRBSDV on rice using reverse-transcription real-time polymerase chain reaction and determined the relationship between virus titer in plants and virus acquisition by S. furcifera. Under a constant temperature of 27°C, a substantial increase of SRBSDV titer in the leaf sheath together with typical symptoms (stunted growth and twisting of leaf tips) was observed at 20 days after the end of a 7-day exposure of viruliferous S. furcifera. Approximately 40% of S. furcifera acquired SRBSDV through feeding for 5 days on rice plants that were infected following exposure to viruliferous vectors for 10 to 15 days. These results suggest that rice infected by S. furcifera can be a source of SRBSDV before the next generation of S. furcifera emerges.

Evidence of recombination and genetic diversity in southern rice black-streaked dwarf virus

Southern rice black-streaked dwarf virus (SRBSDV) causes one of the most serious viral diseases of rice in China and Vietnam. Sequence identities of S10, encoding the major capsid protein, were 98.0%-100% and 98.3%-100% at the nucleotide and amino acid level, respectively. Our results suggest that the codon at position 550 of S10 is under positive selection, while most of the other codons are under neutral evolution. Putative recombination events were identified in genomic RNA segments S1, 2, 4, 5, 6 and 10, which are rare in plant-infecting dsRNA viruses. This study reveals the current state of SRBSDV evolution.

Reverse transcription loop-mediated isothermal amplification of RNA for sensitive and rapid detection of southern rice black-streaked dwarf virus

Southern rice black-streaked dwarf virus (SRBSDV) causes one of the most serious viral diseases of rice in Southeast Asia. A reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed for detection of SRBSDV using total RNA extracted from rice tissues and the insect pest, white-backed planthopper. The assay was based on a set of four primers matching a total of six sequences in the S9 region of SRBSDV genome. Presence of the virus could be detected in RT-LAMP reactions containing 1.2×10(-6)μg of a total RNA extract, which was ten times more sensitive than a classical RT-PCR assay. The SRBSDV could be distinguished from the closely related rice black-streaked dwarf virus (RBSDV) by this method, indicating a high degree of specificity. This simple and sensitive RT-LAMP assay shows potential for detection of SRBSDV in field samples of hosts or vectors at a relatively low cost.

Genetic dissection of the resistance toRice stripe viruspresent in theindicarice cultivar ‘IR24’

Rice stripe disease, caused by Rice stripe virus (RSV) and transmitted by the small brown planthopper (Laodelphax striatellus Fallen), is one of the most serious viral diseases of rice in temperate East Asian production regions. Prior quantitative trait loci (QTL) mapping has established that Oryza sativa L. subsp. indica 'IR24' carries positive alleles at the three loci qSTV3, qSTV7, and qSTV11-i. Here, we report an advanced backcross analysis based on three selected chromosome segment substitution lines (CSSLs), each predicted to carry one of these three QTL. Three sets of BC(4)F(2:3) populations were bred from a cross between the critical CSSL and its recurrent parent Oryza sativa L. subsp. japonica 'Asominori'. Both qSTV3 and qSTV11-i were detected in their respective population, but qSTV7 was not. An allelic analysis based on a known carrier of the major RSV resistance gene Stvb-i, which is located on chromosome 11, showed that qSTV11-i was not allelic with Stvb-i. A large mapping population was used to delimit the location of qSTV11-i to a 73.6-kb region. The de novo markers developed for this purpose will be useful as marker-assisted selection tools in efforts to introduce qSTV11-i into breeding programmes aiming to improve the level of RSV resistance.

Bionomics of vectors and dynamics of rice yellow mottle virus in Tanzania

Rice yellow mottle virus (RYMV) is the only known viral disease of rice in Africa and it is endemic to the continent. It is now the most important disease of rice in Tanzania and is commonly found in lowland rice, which accounts for 80% of the country's rice production. The disease was first observed in Tanzania and Zanzibar in the early 1980s but has only lately drawn research attention. Ali (1999) and Luzi-Kihupi et al (2000) reported that RYMV has been observed in most of the major rice-growing regions in Tanzania and that the disease is spreading at an alarming rate between and within these regions. RYMV is transmitted efficiently by chrysomelid beetles (Bakker 1974). The important vectors in Tanzania are Chaetocnema sp. (a yet to be described species), C. pulla Chapuis, and Dactylispa sp. (not Dactylispa bayoni Gestro) (Banwo et al 2000). However, Dactylispa sp. is believed to be a potentially important vector since it is not found in all RYMV fields.