Purification, properties, and diagnosis of banana bract mosaic potyvirus and its distinction from abaca mosaic potyvirus

Occurrence of Banana bract mosaic virus on Musa ornata Roxb based hybrids in India

Musa ornata, wild species of banana is being used as a cut flower, potted plants and for landscape gardening etc., They are also being utilized in banana hybridization programmes for introgressing pest and disease tolerant traits into banana cultivars in addition to the development of inter specific ornamental banana hybrids. Symptoms of banana bract mosaic virus (BBrMV) was observed in the bracts of interspecific M. ornata based hybrid developed using another wild species i.e., Musa rubra Kurz at ICAR-National Research Centre for Banana (NRCB), Tiruchirapalli. Presence of the virus in the bracts, leaves and roots of symptomatic plants was confirmed through triple antibody sandwich enzyme linked immunosorbent assay with BBrMV monoclonal and polyclonal antibodies. BBrMV HC-Pro (1370 bp), CP (900 bp) and VPg (570 bp) genes were amplified from the infected bracts using reverse transcriptase polymerase chain reaction with BBrMV respective gene primers. The amplicons of these three genes were cloned and sequenced. Blastn analysis revealed that HC-Pro, VPg and CP gene sequences has 97.67%, 97.72% and 99.67% similarity with the respective gene sequences of BBrMV infecting banana. Phylogenetic analysis clustered the test isolate with other BBrMV isolates of banana and other hosts based on CP and HC-Pro and VPg gene sequences. The virus is transmitted through Pentalonia nigronervosa and the transmitted plants expressed symptoms under glass house conditions. To the best of our knowledge, this is the first report of BBrMV on ornamental M. ornata hybrid in India and its transmission occurs through Pentalonia nigronervosa.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-022-00788-6.

A rapid and sensitive lateral flow immunoassay (LFIA) test for the on-site detection of banana bract mosaic virus in banana plants

Banana bract mosaic virus (BBrMV) is a serious pathogen threatening the cultivation of banana and plantain worldwide. This study reports the development of a practical, rapid, sensitive, specific and user-friendly lateral flow immunoassay (LFIA) test for the on-site detection of BBrMV. The BBrMV coat protein (CP) was expressed in Escherichia coli and purified and used to immunize rabbits to produce a polyclonal antiserum (anti-BBrMVCP). The test was based on a double-antibody sandwich format. Protein-A affinity column-purified anti-BBrMVCP Immunoglobulins (IgG) (16 μg/mL), conjugated to ∼30 nm gold nanoparticles, was applied onto the conjugate pad. The anti-BBrMVCP IgG and goat anti-rabbit IgG were printed on the surface of a nitrocellulose filter membrane as the test line and control line, respectively. A positive result could be confirmed visually by the presence of a pink band that developed on the LFIA strip within 5-10 min. The detection limit of the test was 10 ng of the expressed recombinant BBrMV CP (rBBrMVCP), and a 1:20 dilution of the BBrMV-infected crude extract. This LFIA test was validated using 114 banana leaf samples randomly collected from the field and the results indicated a very high diagnostic sensitivity (99.04 %) and specificity (100 %) for the test. A Cohen's kappa coefficient of 0.861 obtained also indicated a very good agreement between the LFIA developed in this study and ELISA. This assay could be adopted by farmers, tissue culture industries and quarantine departments for surveys and surveillance. This is the first report on the development of a LFIA-based test for BBrMV detection.

Complete genome sequencing of banana bract mosaic virus isolate infecting cardamom revealed its closeness to banana infecting isolate from India

The complete genome of banana bract mosaic virus (BBrMV), a Potyvirus belonging to the family Potyviridae causing chlorotic streak disease of cardamom (Elettaria cardamomum) in India was determined for the first time from a naturally infected cardamom var. Njallani Green Gold through reverse transcription PCR using nine sets of primers designed to different overlapping regions of the genome. The complete genome has 9708 nucleotides excluding poly (A) tail and has the genome organization similar to that of BBrMV isolates infecting banana and flowering ginger (Alpinia purpurata). The virus has a single open reading frame of 9372 nucleotides that encodes for a polypeptide of 3124 amino acids which is later cleaved into ten matured proteins. The length and arrangements of different proteins in BBrMV-Cardamom was similar to other BBrMV isolates except for the P1 protein that showed a single amino acid deletion. Comparison with three available complete genome sequences revealed that, BBrMV-Cardamom isolate is more closer to BBrMV-Banana isolate from India (BBrMV-TRY) (96.7% identity) than to BBrMV-Banana isolate from Philippines and flowering ginger isolates from USA (94.5%). Analysis of polyprotein and their individual proteins also showed close identity of BBrMV-Cardamom and BBrMV-TRY. The phylogenetic analysis also suggested that BBrMV-Cardamom isolate is closely related to other BBrMV isolates.

Deep sequencing of banana bract mosaic virus from flowering ginger (Alpinia purpurata) and development of an immunocapture RT-LAMP detection assay

Banana bract mosaic virus (BBrMV) has never been reported in banana plants in Hawaii. In 2010, however, it was detected in a new host, flowering ginger (Alpinia purpurata). In this study, we characterize the A. purpurata isolate and study its spread in flowering ginger in Hawaii. A laboratory study demonstrated that BBrMV could be transmitted from flowering ginger to its natural host, banana, therefore raising a serious concern about the potential risk to the rapidly growing banana industry of Hawaii. To quickly monitor this virus in the field, we developed a robust immunocapture reverse transcription loop-mediated isothermal amplification (IC-RT-LAMP) assay. Deep sequencing of the BBrMV isolate from A. purpurata revealed a single-stranded RNA virus with a genome of 9,713 nt potentially encoding a polyprotein of 3,124 aa, and another predicted protein, PIPO, in the +2 reading-frame shift. Most of the functional motifs in the Hawaiian isolate were conserved among the genomes of isolates from one found in the Philippines and India. However, the A. purpurata isolate had an amino acid deletion in the Pl protein that was most similar to the Philippine isolate. Phylogenetic analysis of an eastern Pacific subpopulation that included A. purpurata was closest in genetic distance to a Southeast Asian subpopulation, suggesting frequent gene flow and supporting the hypothesis that the A. purpurata isolate arrived in Hawaii from Southeast Asia.

Biology, etiology, and control of virus diseases of banana and plantain

Banana and plantain (Musa spp.), produced in 10.3 million ha in the tropics, are among the world's top 10 food crops. They are vegetatively propagated using suckers or tissue culture plants and grown almost as perennial plantations. These are prone to the accumulation of pests and pathogens, especially viruses which contribute to yield reduction and are also barriers to the international exchange of germplasm. The most economically important viruses of banana and plantain are Banana bunchy top virus (BBTV), a complex of banana streak viruses (BSVs) and Banana bract mosaic virus (BBrMV). BBTV is known to cause the most serious economic losses in the "Old World," contributing to a yield reduction of up to 100% and responsible for a dramatic reduction in cropping area. The BSVs exist as episomal and endogenous forms are known to be worldwide in distribution. In India and the Philippines, BBrMV is known to be economically important but recently the virus was discovered in Colombia and Costa Rica, thus signaling its spread into the "New World." Banana and plantain are also known to be susceptible to five other viruses of minor significance, such as Abaca mosaic virus, Abaca bunchy top virus, Banana mild mosaic virus, Banana virus X, and Cucumber mosaic virus. Studies over the past 100 years have contributed to important knowledge on disease biology, distribution, and spread. Research during the last 25 years have led to a better understanding of the virus-vector-host interactions, virus diversity, disease etiology, and epidemiology. In addition, new diagnostic tools were developed which were used for surveillance and the certification of planting material. Due to a lack of durable host resistance in the Musa spp., phytosanitary measures and the use of virus-free planting material are the major methods of virus control. The state of knowledge on BBTV, BBrMV, and BSVs, and other minor viruses, disease spread, and control are summarized in this review.

Complete genome sequence of a banana bract mosaic virus isolate infecting the French plantain cv. Nendran in India

The first complete genome sequence of an Indian isolate (TRY) of Banana bract mosaic virus (BBrMV) was determined following virus RNA extraction from the French plantain cv. Nendran (AAB). The complete genome was 9711 nucleotides excluding the poly(A) tail and had a genome organization similar to that of a Philippine (PHI) isolate characterized earlier. When compared to BBrMV-PHI, the complete genome sequence of BBrMV-TRY was 94% identical at the nucleotide level and its ten mature proteins had amino acid sequence identities ranging from 88 to 98%. Phylogenetic analysis suggests that the BBrMV-TRY isolate is closely related to the BBrMV-PHI isolate.

A reliable IC One-step RT-PCR method for the detection of BBrMV to ensure safe exchange of Musa germplasm

An immunocapture (IC) One-step RT-PCR assay was developed to improve the detection of Banana bract mosaic virus (BBrMV) in single and bulked samples of banana plants. In this paper, an atypical strain of BBrMV was described, the BBrMV "Ref" strain, and we showed that detection with available BBrMV tools using ELISA and RT-PCR approaches was not reliable. Primer sets Bract N1/NR and N2/NR specific to BBrMV were designed and used in RT-PCR and IC-RT-PCR assays with two commercial kits that allow the RT and the PCR reactions to take place simultaneously in the same tube. The new assay enabled detection of BBrMV in leaf extract diluted up to 1 x 10(-10) and in bulked samples of 10 plants, and was proposed as a new international standard to index BBrMV.

Abacá bunchy top virus, a new member of the genus Babuvirus (family Nanoviridae)

Two isolates of a novel babuvirus causing "bunchy top" symptoms were characterised, one from abacá (Musa textilis) from the Philippines and one from banana (Musa sp.) from Sarawak (Malaysia). The name abacá bunchy top virus (ABTV) is proposed. Both isolates have a genome of six circular DNA components, each ca. 1.0-1.1 kb, analogous to those of isolates of Banana bunchy top virus (BBTV). However, unlike BBTV, both ABTV isolates lack an internal ORF in DNA-R, and the ORF in DNA-U3 found in some BBTV isolates is also absent. In all phylogenetic analyses of nanovirid isolates, ABTV and BBTV fall in the same clade, but on separate branches. However, ABTV and BBTV isolates shared only 79-81% amino acid sequence identity for the putative coat protein and 54-76% overall nucleotide sequence identity across all components. Stem-loop and major common regions were present in ABTV, but there was less than 60% identity with the major common region of BBTV. ABTV and BBTV were also shown to be serologically distinct, with only two out of ten BBTV-specific monoclonal antibodies reacting with ABTV. The two ABTV isolates may represent distinct strains of the species as they are less closely related to each other than are isolates of the two geographic subgroups (Asian and South Pacific) of BBTV.

Development of a multiplex immunocapture PCR with colourimetric detection for viruses of banana

A multiplex, immunocapture PCR (M-IC-PCR) was developed for the simultaneous detection of three viruses from crude sap extracts of banana and plantain (Musa spp.). A reverse transcription step was required for Banana bract mosaic virus and Cucumber mosaic virus, which have ssRNA genomes. The detection of Banana bunchy top virus (ssDNA genome) was not adversely affected by inclusion in this step. All the three viruses could be detected simultaneously from a mixed infection. Identification and detection of individual viruses was achieved through the visualisation of discretely sized PCR amplicons by gel electrophoresis. Alternatively, a colourimetric microplate detection system utilising digoxigenin-labelled virus-specific probes was used. The latter assay was up to five times more sensitive than detection by gel electrophoresis and between 25 and 625 times more sensitive than ELISA for the various viruses. Careful selection of PCR primers was necessary to ensure the detection of a wide range of virus isolates and to avoid detrimental interactions between heterologous templates and primers.