Somnath Roy

Identification and characterization of a distinct banana bunchy top virus isolate of Pacific-Indian Oceans group from North-East India

Banana bunch top virus (BBTV) is considered to be a serious threat to banana production. A new isolate of the virus (BBTV-Umiam) was identified and characterized from local banana mats growing in mid-hills of Meghalaya in North-East India. The complete nucleotide sequence analysis revealed the presence of six full-length ssDNA components (DNA R, DNA U3, DNA S, DNA M, DNA C and DNA N) sharing major common region (CR-M) and a stem-loop common region (CR-SL). BBTV-Umiam showed a unique deletion of 20 nucleotides in the intergenic region of DNA R, the absence of predicted open reading frame (ORF) in DNA U3 and probability for a small ORF in DNA U3 expecting functional evidence at transcriptional level. Phylogenetic analysis based on 88 complete nucleotide sequence of BBTV DNA R available in GenBank generated two broad clusters of Pacific-Indian Oceans (PIO) and South-East Asian (SEA) groups including BBTV-Umiam within PIO cluster. However, BBTV-Umiam was identified as the most distinct member of the PIO group with 100% bootstrap support. This was further supported by the phylogenetic grouping of each genomic component of BBTV-Umiam at the distant end of PIO group during clustering of 21 complete BBTV sequences. BBTV-Umiam shared relatively less nucleotide identity with PIO group for each genomic component (85.0-95.4%) and corresponding ORF (93.8-97.5%) than that of earlier PIO isolates (91.5-99.6% and 96.0-99.3%, respectively). Recombination analysis revealed two intra-component and five inter-component recombination events in BBTV-Umiam, but none of them was unique. Moreover, the isolate was identified as major parental sequence for intra-component recombination event spanning the replication-associated protein encoding region in Tongan BBTV DNA R. The current study indicated differential evolution of BBTV in North-East India (Meghalaya). The natural occurrence of hybrids of Musa balbisiana and M. acuminata in this geographically isolated region could be the contributing factor in accumulating genetic distinctiveness in BBTV-Umiam which need further characterization.

Transfer of transgenes for resistance to rice tungro disease into high-yielding rice cultivars through gene-based marker-assisted selection

Rice tungro disease (RTD), caused by the simultaneous infection of rice tungro bacilliform virus (RTBV) and rice tungro spherical virus (RTSV), is one of the major threats to sustainable rice production in South and Southeast Asia. Transgenic resistance against RTBV has been reported previously using an RNA interference (RNAi) construct (ORF IV of RTBV, placed both in sense and anti-sense orientation under CaMV 35S promoter), in the scented rice line Pusa Basmati-1 (PB-1). This construct was transferred to two high-yielding tungro-susceptible indica rice cultivars (IET4094 and IET4786) from the transgenic PB-1 rice line using back cross breeding till the BC 2 F 3 stage. On challenge inoculation, the progenies (BC 2 F 1 ) showed mild symptoms of tungro, in contrast to severe symptoms displayed by the recurrent parents. Segregation of the transgene indicated near homozygosity of the plants at the BC 2 F 3 stage, implying that the lines can be used as a valuable resistance source for further breeding against RTD.

Phylogenetic analysis of Rice tungro bacilliform virus ORFs revealed strong correlation between evolution and geographical distribution

A new isolate of Rice tungro bacilliform virus (RTBV) was collected from Chinsura, West Bengal, India. The full genome was sequenced and deposited to GenBank designating the new one as Chinsura isolate. The four open reading frames (ORFs) of the new isolate were compared with those of previously reported ‘South-east Asian’ (SEA) and ‘South Asian’ (SA) isolates emphasizing the ORF3, which is the largest and functionally most important gene of RTBV. In the ORFs, Chinsura isolate shared 90.0–100.0% identity at amino acid level with SA isolates, but only 58.76–88.63% identity with SEA isolates for the same. Similarly, the amino acid identity of ORFs between SEA and SA isolates ranged from 58.77 to 88.64, whereas within each group the corresponding value was >96.0%. The phylogenetic analysis based on nucleotide and amino acid sequences of each ORF made two broad clusters of SEA- and SA-types including Chinsura isolate within SA cluster. Moreover, the relative positions and length of functional domains corresponding to movement protein (MP), coat protein (CP), aspartate protease (PR) and reverse transcriptase/ribonuclease H (RT/RNase H) of ORF3 of Chinsura isolate were completely identical with SA isolates. The clustering pattern indicated strong influence of geographical habitat on genomic evolution. Comparison of ORF3 among all the isolates revealed major variations at non-functional regions in between the functional domains and at the hypervariable 3′-terminal end of ORF3, while PR appeared to have evolved differentially in SA isolates expecting further characterization.

First report of Chilli veinal mottle virus in Naga chilli (Capsicum chinense) in Meghalaya, India

The present study confirms the occurrence of Chilli veinal mottle virus (ChiVMV) under the genus Potyvirus in Naga chilli (Capsicum chinense) in Meghalaya based on mechanical transmission assay, transmission electron microscopy, RT-PCR and sequence analysis. This is the first record of Chivmv in Naga chilli in North-East India.

Phenotypic characterization of indigenous rice ( Oryza sativa L.) germplasm collected from the state of Nagaland, India

Nagaland is one of the eight states in the north-eastern region of India, where a considerable diversity exists in cultivated rice. Recent exploration in this tribal-dominated state has resulted in a collection of 130 rice accessions growing under diverse agroecological conditions. The agromorphological characterization data of 124 rice landraces revealed a significant variability in plant architecture and grain morphological and quality traits. Multivariate analyses including principal component analysis (PCA) and cluster analysis were performed to assess the patterns of morphological variation. The PCA extracted 12 components, which explained 75.4% of the total variation for 38 quantitative and qualitative traits. The cluster analysis grouped 124 rice landraces into five clusters, and the number of landraces in each cluster ranged from 1 to 59. The correlations among the traits are discussed, which will be useful in considering traits for genetic improvement in grain yield and quality. The landraces have been conserved in the national genebank for further utilization.

The large intergenic region of Rice tungro bacilliform virus evolved differentially among geographically distinguished isolates

Rice tungro bacilliform virus (RTBV) is a plant pararetrovirus. The large intergenic region (LIGR) of RTBV having a single transcriptional promoter produces more than genome length pregenomic RNA (pgRNA) which directs synthesis of circular double-stranded viral DNA and serves as a polycistronic mRNA. By computer-aided analysis of LIGR, the 11 RTBV isolates sequenced so far were compared with respect to structural organization of promoter and pgRNA 5′-leader. The results revealed only 74.90% identity at LIGR between ‘Southeast Asian’ (SEA) and ‘South Asian’ (SA) isolates of RTBV indicating considerable variation between two groups which was also reflected during analysis of promoter and leader sequence. The predicted promoter region of SA isolates exhibited major variations in terms of transcription start site and consensus sequences of cis motifs expecting further exploitation of promoter region of SA isolates. The reduced length of leader sequence along with less numbers and different arrangements of small open reading frames (sORFs) in case of SA isolates might have some alterations in the control of expression of ORF II and III between the two groups. In spite of these variations, the leader sequence of both SEA and SA type isolates showed formation of stable secondary or stem-loop structure having identical features for efficient translation. The conservation of sORF1 at seven nucleotides upstream of stable stem-loop, CU-rich sequence following the sORF1 stop codon and AU-rich shunt landing sequence immediately downstream of the secondary structure suggested conservation of ribosomal shunt mechanism in all RTBV isolates irrespective of their geographical distribution.

Detection of probable marker-free transgene-positive rice plants resistant to rice tungro disease from backcross progenies of transgenic Pusa Basmati 1

. 2004). Biotechnologicalapproaches have also been employed to develop transgenicplants for resistance against RTBV and RTSV (for reviewsee Dai and Beachy 2009). The transgenic strategies for RTDresistance are promising, although pathogen derived resis-tance for RTD has reported as being only partially effective

Collection and phenotypic characterisation of pole-type common bean (Phaseolus vulgaris L.) landraces from Mizoram

Common beans are one of the many important food legumes grown in India. In the hilly regions of north-eastern India farmers mostly grow the pole-type beans by intercropping beans with maize, and in backyardsand kitchen gardens. In this study, we characterized a set of 52 pole-type common bean landraces collectedfrom the state of Mizoram for 23 agro-morphological and quality traits. Remarkable variability was observedfor almost all the traits. Wide range of variability was found for the traits such as leaf length (7.5–18.0 cm), leafbreadth (6.2–12.8 cm) days to flowering (33–70 days), pods per plant (7.7–24.0), pod length (8.1–14.6 cm), podyield per plant (61.5–182.3 g), seeds per pod (4.6–8.0), 100-seed weight (23.0–50.1 g) and crude protein content(20–33.8%). Positively significant correlation coefficients were observed between 100-seed weight and daysto flowering; number of pods per plant and pod yield per plant. The patterns of morphological variation wereassessed using multivariate approaches. Five morphologically distinct clusters were identified within thecollected germplasm. The evolutionary grouping of the common bean landraces has been discussed consideringthe morphological features.