RESUMO
Rice crops in South and Southeast Asian countries suffer critical yield losses due to rice tungro disease caused by joint infection with rice tungro bacilliform virus (RTBV) and rice tungro spherical virus (RTSV). Previously, for generating RNA interference-based transgenic resistance against tungro viruses, RTBV ORF IV was used as a transgene to develop RTBV resistance in a popular high-yielding scented rice variety. The transgene from this line was then introgressed into five popular high-yielding but tungro-susceptible rice varieties by marker-assisted backcross breeding with a view to combine the resistant trait with the agronomic traits. The present work includes a resistance assay of the BC3F5 lines of these varieties under glasshouse conditions. Out of a total of 28 lines tested, each consisting of 12 individual plants, eight lines showed significant amelioration in height reduction and 100- to 1000-fold reduction in RTBV titers. The RNAi-mediated resistance was clearly manifested by the presence of virus-derived small RNA (vsRNA) specific for RTBV ORF IV in the transgenic backcrossed lines.
Assuntos
Resistência à Doença , Oryza/imunologia , Doenças das Plantas/virologia , Plantas Geneticamente Modificadas/imunologia , Tungrovirus/fisiologia , Proteínas Virais/genética , Índia , Oryza/genética , Oryza/virologia , Doenças das Plantas/imunologia , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/virologia , Interferência de RNA , Transgenes , Tungrovirus/genética , Tungrovirus/isolamento & purificação , Proteínas Virais/metabolismo , Waikavirus/genética , Waikavirus/metabolismoRESUMO
Severe losses of rice yield in south and southeast Asia are caused by Rice tungro disease (RTD) induced by mixed infection of Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV). In order to develop transgene-based resistance against RTBV, one of its genes, ORF IV, was used to generate transgenic resistance based on RNA-interference in the easily transformed rice variety Pusa Basmati-1, and the transgene was subsequently introgressed to rice variety ASD 16, a variety popular in southern India, using transgene marker-assisted selection. Here, we report the evaluation of BC3F4 and BC3F5 generation rice plants for resistance to RTBV as well as for agronomic traits under glasshouse conditions. The BC3F4 and BC3F5 generation rice plants tested showed variable levels of resistance, which was manifested by an average of twofold amelioration in height reduction, 1.5-fold decrease in the reduction in chlorophyll content, and 100- to 10,000-fold reduction in the titers of RTBV, but no reduction of RTSV titers, in three backcrossed lines when compared with the ASD 16 parent. Agronomic traits of some of the backcrossed lines recorded substantial improvements when compared with the ASD 16 parental line after inoculation by RTBV and RTSV. This work represents an important step in transferring RTD resistance to a susceptible popular rice variety, hence enhancing its yield in areas threatened by the disease.
Assuntos
Resistência à Doença/genética , Genes de Plantas/genética , Oryza/virologia , Doenças das Plantas/genética , Transgenes/genética , Waikavirus/genética , Cruzamento , Índia , Fases de Leitura Aberta/genética , Oryza/genética , Doenças das Plantas/virologia , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/virologia , Interferência de RNA/fisiologia , RNA Viral/genéticaRESUMO
The complete nucleotide sequence of Sri Lankan cassava mosaic virus (SLCMV) DNA-A isolated from cassava in southern India was analyzed, a phylogenetic analysis with other begomoviral nucleotide sequences was performed and an efficient inoculation method of Nicotiana benthamiana with the cloned DNA was developed utilizing a biolistic device. The nucleotide sequence showed the conservation of all functional begomoviral protein domains and aligned most closely with begomoviruses reported from the Indian subcontinent, except for begomoviruses of cucurbits and legumes. Upon biolistic inoculation of N. benthamiana with the cloned DNA, most plants became symptomatic and showed the accumulation of viral DNA within 21-28 days post-inoculation.
Assuntos
Begomovirus/classificação , Begomovirus/patogenicidade , Nicotiana/virologia , Filogenia , Doenças das Plantas/virologia , Begomovirus/genética , Begomovirus/isolamento & purificação , Biolística , DNA Viral/genética , DNA Viral/metabolismo , Índia , Manihot/virologia , Dados de Sequência Molecular , VirulênciaRESUMO
Blast disease caused by the pathogen Pyricularia oryzae is a serious threat to rice production. Six generations viz., P1, P2, F1, F2, B1 and B2 of a cross between blast susceptible high-yielding rice cultivar ADT 43 and resistant near isogenic line (NIL) CT13432-3R, carrying four blast resistance genes Pi1, Pi2, Pi33 and Pi54 in combination were used to study the nature and magnitude of gene action for disease resistance and yield attributes. The epistatic interaction model was found adequate to explain the gene action in most of the traits. The interaction was complementary for number of productive tillers, economic yield, lesion number, infected leaf area and potential disease incidence but duplicate epistasis was observed for the remaining traits. Among the genotypes tested under epiphytotic conditions, gene pyramided lines were highly resistant to blast compared to individuals with single genes indicating that the nonallelic genes have a complementary effect when present together. The information on genetics of various contributing traits of resistance will further aid plant breeders in choosing appropriate breeding strategy for blast resistance and yield enhancement in rice.
Assuntos
Resistência à Doença/genética , Epistasia Genética , Magnaporthe/imunologia , Oryza/genética , Doenças das Plantas/genética , Cruzamento , Genes de Plantas , Estudos de Associação Genética , Oryza/imunologia , Doenças das Plantas/imunologiaRESUMO
Yellow mosaic disease caused by mungbean yellow mosaic virus (MYMV) belonging to the genus Begomovirus (the family Geminiviridae) is a major constraint in cultivation of grain legumes in India. The urdbean (Vigna mungo (L.) Hepper) and mungbean (Vigna radiata (L.) R. Wilczek) samples affected with yellow mosaic disease exhibits yellow mosaic symptoms along with leaf puckering and leaf distortion in Tamil Nadu. Hence the study was performed to find out if there was any association and influence of betasatellite DNA on the symptom expression of MYMV. Full length viral clones of DNA A and DNA B were obtained through rolling circle amplification from YMD infected samples and identified as mungbean yellow mosaic virus. Interestingly, betasatellite was found to associate with MYMV, and its nucleotide sequence analysis showed its 95% identity with papaya leaf curl betasatellite (DQ118862) from cowpea. The present study represents the first report about the association of papaya leaf curl betasatellite with MYMV and represents a new member of the emerging group of bipartite begomovirus associated with betasatellite DNA.
Assuntos
Begomovirus/fisiologia , DNA Satélite/genética , DNA Viral/genética , Fabaceae/virologia , Genoma Viral , Doenças das Plantas/virologia , Vírus Satélites/genética , Sequência de Aminoácidos , Sequência de Bases , Begomovirus/genética , Begomovirus/isolamento & purificação , DNA Satélite/química , DNA Satélite/metabolismo , DNA Viral/química , DNA Viral/metabolismo , Índia , Dados de Sequência Molecular , Filogenia , Folhas de Planta/virologia , Vírus Satélites/química , Vírus Satélites/isolamento & purificação , Vírus Satélites/fisiologia , Alinhamento de SequênciaRESUMO
The complete nucleotide sequence of an isolate of rice tungro bacilliform virus (RTBV), collected from Kanyakumari, India, where RTBV was reported recently for the first time, has been analyzed. Sequence comparison revealed that the RTBV isolate from Kanyakumari (RTBV-KK) has a high degree of identity to the two previously reported RTBV sequences from India, RTBV-AP and RTBV-WB, which had been collected from field locations about 10 years ago and 1000-2000 km away from the collection site of RTBV-KK. Most of the sequence domains reported previously in other RTBV isolates were found to be conserved in RTBV-KK. Closer inspection revealed RTBV-KK to be a possible recombinant between RTBV-AP and RTBV-WB in the genomic region encompassing the coat protein gene.
Assuntos
DNA Viral/genética , Oryza/virologia , Doenças das Plantas/virologia , Tungrovirus/genética , Proteínas do Capsídeo/genética , Variação Genética , Genoma Viral , Índia , Dados de Sequência Molecular , Filogenia , Recombinação Genética , Homologia de Sequência de Aminoácidos , Homologia de Sequência do Ácido Nucleico , Tungrovirus/classificação , Tungrovirus/isolamento & purificaçãoRESUMO
The objective of this study is to describe the time of onset of contractions in twin pregnancies that result in delivery, so as to investigate whether there is a diurnal influence. A UK maternity department database was used to identify twin deliveries over a 5-year period, and the time of onset of labour was retrieved from these records. Two hundred and eleven women with spontaneous onset of labour in twin pregnancies were studied. A significant diurnal rhythm in the timing of contractions was noted, with 45% of deliveries occurring in labour that commenced between midnight and 08.00 hours. This periodicity is similar for twin pregnancies that end in preterm (24-36 weeks of gestation; χ² = 17.2; P < 0.01) or term deliveries (37-40 weeks of gestation; χ² = 13; P < 0.05). The periodicity of onset of labour in multiple pregnancies demonstrates a similar rhythm to singleton pregnancies, where labour most commonly begins between midnight and 08.00 hours.
