Banana Streak Virus Research Articles

Prevalence and diversity of Banana streak viruses in the Dominican Republic

An extensive survey was carried out in the Dominican Republic in order to monitor the prevalence of the three most widespread BSV species: Banana streak OL virus (BSOLV), Banana streak GF virus (BGFV) and Banana streak IM virus (BSIMV), in Macho x Hembra (MxH) and FHIA-21 plantains and in Cavendish dessert banana throughout all banana-producing areas. This survey led to the first detection of BSVs in the Dominican Republic. BSGFV was the most prevalent of the three targeted BSV species in both FHIA-21 and MxH varieties. Prevalence of BSGFV and BSOLV were substantially higher in FHIA-21 than in MxH. Molecular analysis of the eBSV pattern of sampled FHIA-21 and MxH plants showed that both varieties harbor infectious alleles OL1 (eBSOLV) and GF7 (eBSGFV) and are devoid of eBSIMV. Very low prevalence was recorded for both BSOLV and BSGFV in Cavendish banana, which is devoid of infectious eBSVs. BSIMV was not detected at all. Our results point to a marginal role of insect-borne transmission in the epidemiology of BSVs in the Dominican Republic.

The complete genome of Banana streak GF virus Yunnan isolate infecting Cavendish Musa AAA group in China.

Banana streak virus (BSV) belongs to the members of the genus Badnavirus, family Caulimoviridae. At present, BSV contains nine species in the International Committee on Taxonomy of Viruses (ICTV) classification report (2018b release). Previous study indicated that the viral particles of Banana streak virus Acuminata Yunnan (BSV-Acum) were purified from banana (Cavendish Musa AAA group) leaves in Yunnan Province, China, and its complete genome was obtained. To further determine whether this sample infecting with Banana streak GF virus (BSGFV), the polymerase chain reaction (PCR) cloning and complete genome analysis of the Banana streak GF virus Yunnan isolate (BSGFV-YN) isolate were carried out in this study. The result showed that BSGFV-YN infecting Cavendish Musa AAA group was co-infecting this sample. Its genome contains a total of 7,325 bp in length with 42% GC content. This complete genome sequence was deposited in GenBank under accession number MN296502. Sequence analysis showed that the complete genome of BSGFV-YN was 98.14% sequence similarity to BSGFV Goldfinger, while it was 49.10–57.09% to other BSV species. Two phylogenetic trees based on the complete genome and ORFIII polyprotein indicated that BSGFV-YN and other BSV species clustered into a group, while it was the highest homology with BSGFV Goldfinger. Although BSGFV-YN and BSGFV Goldfinger were highly homologous, their cultivating bananas are different. The former cultivating banana was from Cavendish Musa AAA group, while the latter cultivating banana was from Goldfinger Musa AAAB group. Compared with BSGFV Goldfinger, the genome of BSGFV-YN has an extra multiple repetitive sequences in the intergenetic region between ORFIII and ORFI, suggesting that this region might be related to host selection. In summary, a BSGFV-YN distant from BSV-Acum was identified from the same sample, and its complete genome sequence was determined and analyzed. The study extends the polymorphism of BSVs in China and provides scientific clue for the evolutionary relationship with host selection of badnaviruses.

First Report of Banana Streak Virus Infecting Bananas (Musa spp.) in Georgia, U.S.A.

Banana streak virus (BSV) is a badnavirus containing a circular dsDNA genome of 7.4 kb that causes a viral leaf streak disease of banana (Musa spp.) worldwide (Dallot et al. 2001). On bananas, typical symptoms of BSV include broken or continuous chlorotic streaks or spindle-shaped patterns that are first chlorotic, become increasingly dark in color, and subsequently result in black streaking in older leaves (Dallot et al. 2001). In the summer of 2019, six symptomatic leaves from three different plants were collected from the University of Georgia Banana Research Plot, Tifton, GA. The cultivar is ‘Pisang Awak’, and it belongs to the tetraploid AABB genome group. Initial identification was performed by assessing disease symptoms including chlorotic streaks on leaves that became brown and black chlorotic streaks later, resembling those of banana streak disease (Lockhart 1986). BSV was verified via molecular and serological tests. Genomic DNA from leaf tissue of three different symptomatic plants and two healthy plants was extracted using a DNeasy Plant Mini Kit (Qiagen, Valencia, CA). Samples were tested for the presence of BSV by two separate PCR amplification methods. One was targeting the aspartic protease (AP) and reverse transcription (RT) regions of ORF3 using primer pair BSV 4673 (5′-GGAATGAAAGAGCAGGCC-3′) and BSV 5317 (5′-AGTCATTGGGTYCAACCTCTGTCCC-3′) with an amplicon size of 644 bp (Manoranjitham et al. 2012). Another PCR analysis was targeting the coat protein (CP) region of ORF3 with primer pair BSV 156 (5′-TTACCTCCAGCACAAAGTCG-3′) and BSV 962 (5′-TTCTCCACAGGCATAACACC-3′) designed in this study with a product size of 806 bp. Both PCR reactions for all six symptomatic samples produced the expected sizes of the fragments for BSV; however, two samples from the healthy plants did not produce any bands. The amplified products were then sequenced and subjected to BLAST analysis for further identification. Sequence analysis revealed that the obtained partial sequence of the AP and RT region (MN567071) shared 100% identity to corresponding sequences from BSV OL virus isolate BSOLV-IN2 (accession no. JQ409540). Furthermore, the obtained CP gene sequence (MN567072) also showed 100% identity with BSV isolate BSOLV-IN2. Samples were also tested for the presence of BSV by real-time PCR with primers BSV 1075 (5′-CACATTGACGGAAAGGACAACG-3′) and BSV 1198 (5′-TGTGAAATACCTCCTCCACTGC-3′) targeting the RNase H gene (Delanoy et al. 2003), and the results confirmed its identity as BSV. In addition to the molecular tests, a DAS-ELISA test was carried out on the remaining symptomatic leaf tissues for further confirmation of BSV according to the manufacturer’s protocol (Nano Diagnostics, Fayetteville, AR). All three samples tested by ELISA were positive for BSV. To the best of our knowledge, this is the first report of BSV infecting Musa spp. in Georgia. This virus could pose an imminent threat to the newly growing banana industry in this area if it spread in banana fields under conditions in Georgia. Our findings will be helpful for banana growers in Georgia by taking appropriate control strategies to combat this viral disease. Further research is needed to elucidate epidemiology, symptomatology, vector transmission, and crop losses due to BSV in Georgia and the United States.

Yield and Fruit Quality Traits of Two Plantain Cultivars Grown at Two Locations in Puerto Rico under Black Leaf Streak Disease Pressure

Plantain (Musa balbisiana AAB) is a tropical rhizomatous perennial plant in the genus Musa spp., closely related to banana (Musa acuminata AAA). It is an important cash crop and staple for inhabitants in many parts of the world, including various ethnic groups in the United States. Black leaf streak disease (BLSD) or black sigatoka, caused by Pseudocercospora fijiensis (formerly Mycosphaerella fijiensis), is responsible for significant losses of this crop due to the high susceptibility of the most economically important cultivars. BLSD does not immediately kill plantain plants, but it causes severe leaf necrosis, which results in reduced photosynthetic area, thereby adversely impacting bunch weight and fruit production. Without cultural and chemical control, yields can be reduced by 20% to 80%, depending on severity. This study evaluated a BLSD-resistant cultivar, FHIA-21, against Maricongo, a standard commercial cultivar with no BLSD tolerance, at two locations in Puerto Rico on Ultisol (Corozal site) and Oxisol (Isabela site) soils. Total number of fruit and bunch yield were significantly higher at Isabela, with BLSD severity being significantly lower at this location. Average fruit production of ‘FHIA-21’ was significantly higher than that of ‘Maricongo’ at both locations, with fruit yields of 122,522 and 99,948 fruit/ha at Isabela and Corozal, respectively. Overall, fruit of ‘FHIA-21’ were significantly longer and had greater diameters than those of ‘Maricongo’. At Isabela, the mean bunch fruit weight was significantly higher for ‘FHIA-21’, but both cultivars exceeded the minimum local marketable fruit weight criterion of 270 g. At both locations, the numbers of functional leaves present at flowering and at harvest were significantly higher for ‘FHIA-21’ than for ‘Maricongo’, indicating more availability of photosynthetic area for ‘FHIA-21’ during the fruit-filling period. There were no significant differences between cultivars regarding the concentration of starch and soluble sugars for green fruit. Regarding ripe fruit, ‘FHIA-21’ had a significantly higher concentration of soluble sugars and less starch. In this study, ‘FHIA-21’ had good resistance against BLSD and, if accepted by consumers, is a viable alternative to current commercial cultivars. We also conclude from this study that the expression of the Banana streak virus (BSV) in planting material of this cultivar remains an unknown threat in yield decline of ‘FHIA-21’.

Detection of episomal banana streak Mysore virus by reverse transcription-recombinase polymerase amplification assay

Banana streak viruses (BSVs) are considered a major constraint to banana production worldwide. The integrated BSV sequence in the banana genome makes the nucleo-based detection unreliable and the serological-based methods require high quality polyclonal antiserum. In this study, reverse transcription-recombinase polymerase amplification (RT-RPA) assay was developed for a specific amplification of episomal banana streak Mysore virus (BSMYV) in different banana cultivars. A total of 50 symptomatic and asymptomatic leaf samples of different banana cultivars were evaluated and BSMYV was efficiently detected by RT-RPA using a crude leaf sap template. Similar results were obtained with conventional reverse transcription-polymerase chain reaction (RT-PCR) using purified RNA as template. RT-RPA was significantly faster than RT-PCR with results obtained in less than one hour. The rapid and reliable diagnosis of episomal BSMYV will be most useful for virus indexing in plants including the banana tissue culture certification programme.

CRISPR/Cas9 editing of endogenous banana streak virus in the B genome of Musa spp. overcomes a major challenge in banana breeding

Presence of the integrated endogenous banana streak virus (eBSV) in the B genome of plantain (AAB) is a major challenge for breeding and dissemination of hybrids. As the eBSV activates into infectious viral particles under stress, the progenitor Musa balbisiana and its derivants, having at least one B genome, cannot be used as parents for crop improvement. Here, we report a strategy to inactivate the eBSV by editing the virus sequences. The regenerated genome-edited events of Gonja Manjaya showed mutations in the targeted sites with the potential to prevent proper transcription or/and translational into functional viral proteins. Seventy-five percent of the edited events remained asymptomatic in comparison to the non-edited control plants under water stress conditions, confirming inactivation of eBSV into infectious viral particles. This study paves the way for the improvement of B genome germplasm and its use in breeding programs to produce hybrids that can be globally disseminated.

Seed degeneration of banana planting materials: strategies for improved farmer access to healthy seed

Vegetatively propagated crops suffer from yield loss and reduced stand density and longevity caused by the build‐up of certain pests and pathogens between successive plantings via infected planting material. Here, six seedborne phytosanitary problems of banana are reviewed to evaluate whether a seed degeneration framework is a useful tool to identify approaches to achieve healthier planting materials. Phytoparasitic nematodes and weevils generate gradual declines in yields and in sucker health. Fusarium wilt and banana bunchy top virus cause progressive mat collapse across the field. Symptomless suckers from any mat in infested fields represent a risk of transmitting the disease to a new field. Xanthomonas and ralstonia wilts, due to incomplete systemicity, are intermediate in their threat to yield loss and frequency of transmission in suckers. Losses to banana streak virus are triggered by abiotic stress, although sucker transmission of episomal banana streak virus also contributes. A qualitative equation described here for seed degeneration covers a cycle beginning with the quality and risk factors of the planting material used to plant a new field and ends with the quality and risk factors of the suckers extracted from the field to plant a new field. This review of five planting material multiplication methods commonly used in banana contrasts their differing usefulness to address seed degeneration in the small farm context. It is proposed that initiatives to offset banana seed degeneration should integrate the role of off‐farm actors into decentralized initiatives rather than attempt to duplicate national seed certification frameworks from other true seed or vegetatively propagated crops.

Multiplex detection of three banana viruses by reverse transcription loop-mediated isothermal amplification (RT-LAMP)

Banana bunchy top virus (BBTV), banana streak viruses (BSVs) and cucumber mosaic virus (CMV) are frequently reported infecting bananas globally. Effective control of their spread depends on robust detection of these viruses in propagation stock, planting material, infected nursery plants, and through strict quarantine. We developed single reverse transcription loop-mediated isothermal amplification (RT-LAMP) assays for BBTV, banana streak OL virus (BSV-OL) and CMV that were sensitive, specific, efficient, and completed in less than 60 min. RNA-based RT-LAMP minimized false positives that arose from banana genomes harboring endogenous viral genomes, such as BSVs. RT-LAMP was also more sensitive than RT-PCR in detecting the DNA viruses, BBTV and BSV-OL, in infected plants. We also developed a multiplex assay using three sets of primers specific for each virus to simultaneously detect BBTV, BSV-OL and CMV in a sample of RNA from the same plant. The reliability and convenience of this assay makes it useful for plant quarantine and indexing plants for propagation.

‘CARBAP K74’: a triploid plantain-like hybrid designed to promote sustainable plantain-based cropping systems

'CARBAP K74' is a triploid plantain-like hybrid developed and selected in partnership between CARBAP and CIRAD. It results from a cross between an improved plantain-like tetraploid (AAAB) parental line and an improved cooking-type diploid (AA). Molecular studies showed that this hybrid is free of any endogenous banana streak virus (eBSV) sequence. An agronomic evaluation was performed over two crop cycles to quantify its productivity and evaluate its host reaction to pests and diseases. A first plot received non-limiting cropping conditions to allow it to reach its highest agronomic potential. A second plot reproduced traditional management in West and Central Africa with low inputs and traditional practices. Agronomic traits at flowering described a robust plant with great anchorage and large green leaf area. Bunch weights ranged from 10 to 50 kg across the two cropping conditions, with an average of 16.4 kg (14 t ha-1 year-1) under traditional management, and 34.3 kg (46 t ha-1 year-1) for non-limiting cropping conditions. In both plots, damage assessments highlighted a lower susceptibility to major pests and diseases of plantains. The agronomic potential of 'CARBAP K74' allows the production of acceptable yields with few inputs over several cycles without replanting, which confirms its interest for smallholders as well as for agroindustry. Furthermore, fruit post-harvest traits and consumer testing showed that 'CARBAP K74' is a promising candidate for consumption and processing. Thus, 'CARBAP K74' is an innovative promising hybrid, which could help farmers to achieve agronomic performance, limit environmental impacts of banana production and confront food security issues.

Analysis of synonymous codon usage bias and phylogeny of coat protein gene in banana bract mosaic virus isolates.

The banana is one of the world's most important livelihood crops. Banana plants are principally infected by four virus species, Banana bunchy top virus (genus Babuvirus), Cucumber mosaic virus (genus Cucumovirus), Banana streak virus (genus Badnavirus) and Banana bract mosaic virus (genus Potyvirus). The objective of this study is to understand the codon usage pattern and phylogeny of coat protein gene in different banana bract mosaic virus (BBrMV) isolates. The BBrMV Coat Protein (CP) gene was amplified from BBrMV infected banana plant samples collected from different districts of Tamil Nadu and Karnataka, India. Six new BBrMV isolates were submitted to National Center for Biotechnology Information. Phylogenetic analysis and codon usage indices were studied along with other isolates of BBrMV. Phylogenetic analysis of CP genes shows that most of BBrMV isolates are closely related to each other except KF385484.1 and KF385478.1. Relative codon usage patterns among different BBrMV isolates were calculated by software CodonW version 1.4.2. In BBrMV, codons with A-ended or U ended are the most preferential except the Leu and Gln whose optimized codons are CAG and UUG ending by G. The codon usage patterns of BBrMV isolates are principally influenced by mutational bias; however, compositional constraints along with mutational bias also play a major role.

Characterization of the banana streak virus capsid protein and mapping of the immunodominant continuous B-cell epitopes to the surface-exposed N terminus.

This study identified the structural proteins of two badnavirus species, Banana streak MY virus (BSMYV) and Banana streak OL virus (BSOLV), and mapped the distribution of continuous B-cell epitopes. Two different capsid protein (CP) isoforms of about 44 and 40 kDa (CP1 and CP2) and the virion-associated protein (VAP) were consistently associated with purified virions. For both viral species, the N terminus of CP2 was successfully sequenced by Edman degradation but that of CP1 was chemically blocked. De novo peptide sequencing of tryptic digests suggested that CP1 and CP2 derive from the same region of the P3 polyprotein but differ in the length of either the N or the C terminus. A three-dimensional model of the BSMYV-CP was constructed, which showed that the CP is a multi-domain structure, containing homologues of the retroviral capsid and nucleocapsid proteins, as well as a third, intrinsically disordered protein region at the N terminus, henceforth called the NID domain. Using the Pepscan approach, the immunodominant continuous epitopes were mapped to the NID domain for five different species of banana streak virus. Anti-peptide antibodies raised against these epitopes in BSMYV were successfully used for detection of native virions and denatured CPs in serological assays. Immunoelectron microscopy analysis of the virion surface using the anti-peptide antibodies confirmed that the NID domain is exposed on the surface of virions, and that the difference in mass of the two CP isoforms is due to variation in length of the NID domain.

Marker-assisted breeding of Musa balbisiana genitors devoid of infectious endogenous Banana streak virus sequences

Breeding new interspecific banana hybrid varieties relies on the use of Musa acuminata and M. balbisiana parents. Unfortunately, infectious alleles of endogenous Banana streak virus (eBSV) sequences are present in the genome of Musa balbisiana genitors. Upon activation by biotic and abiotic stresses, these infectious eBSVs lead to spontaneous infections by several species of Banana streak virus in interspecific hybrids harboring both Musa acuminata and M. balbisiana genomes. Here we provide evidence that seedy M. balbisiana diploids display diverse eBSV allelic combinations and that some eBSVs differ structurally from those previously reported. We also show that segregation of infectious and non-infectious eBSV alleles can be achieved in seedy M. balbisiana diploids through self-pollination or chromosome doubling of haploid lines. We report on the successful breeding of M. balbisiana diploid genitors devoid of all infectious eBSV alleles following self-pollination and on the potential of breeding additional M. balbisiana diploid genitors free of infectious eBSVs by crossing parents displaying complementary eBSV patterns. Our work paves the way to the safe use of M. balbisiana genitors for breeding banana interspecific hybrid varieties with no risk of activation of infectious eBSVs.

Chromosome segregation in an allotetraploid banana hybrid (AAAB) suggests a translocation between the A and B genomes and results in eBSV-free offsprings

Many banana cultivars (including the Plantain type) are triploid interspecific hybrids between Musa acuminata (A genome) and Musa balbisiana (B genome). M. balbisiana contains endogeneous Banana streak virus sequences (eBSVs) that can, in interspecific genome context, spontaneously release infectious viral genomes. We analyzed, a triploid progeny of 184 individuals from a cross between a tetraploid AAAB breeding accession (CRBP39) and the diploid AA accession (Pahang) with 38 SSR and eBSV-specific PCR markers. The results showed that (1) most of the alleles are found/transmitted in the expected frequency to the progeny with only 10 % biased; (2) 70 % of the loci displayed a tetrasomic allele segregation and (3) interspecific intrachromosomal recombinations occurred for all the chromosome segments surveyed. However, half of the offspring obtained resulted from maternal unbalanced gametes transmission. Analysis of gamete composition and marker association suggested the presence of a large translocation between A and B genome involving chromosome 1 and 3. The two infectious eBSVs present in the maternal parent CRBP39 are located on chromosome 1B and appeared in a higher proportion than expected in the progeny. Interestingly, we showed that both eBSVs were absent from 24 offspring that represent promising material for breeding.

How endogenous plant pararetroviruses shed light onMusaevolution

Banana genomes harbour numerous copies of viral sequences derived from banana streak viruses (BSVs) - dsDNA viruses belonging to the family Caulimoviridae.These viral integrants (eBSVs) are mostly defective, probably as a result of 'pseudogenization' driven by host genome evolution. However, some can give rise to infection by releasing a functional viral genome following abiotic stresses. These distinct infective eBSVs correspond to the three main widespread BSV species (BSOLV, BSGFV and BSIMV), fully described within the Musa balbisiana B genomes of the seedy diploid 'Pisang Klutuk Wulung' (PKW). We characterize eBSV distribution among a Musa sampling including seedy BB diploids and interspecific hybrids with Musa acuminate exhibiting different levels of ploidy for the B genome (ABB, AAB, AB). We used representative samples of the two areas of sympatry between M. acuminate and M. balbisiana species representing the native area of the most widely cultivated AAB cultivars (in India and in East Asia, ranging from the Philippines to New Guinea). Seventy-seven accessions were characterized using eBSV-related PCR markers and Southern hybridization approaches. We coded both sets of results to create a common dissimilarity matrix with which to interpret eBSV distribution. We propose a Musa phylogeny driven by the M. balbisiana genome based on a dendrogram resulting from a joint neighbour-joining analysis of the three BSV species, showing for the first time lineages between BB and ABB/AAB hybrids. eBSVs appear to be relevant phylogenetic markers that can illustrate theM. balbisiana phylogeography story. The theoretical implications of this study for further elucidation of the historical and geographical process of Musa domestication are numerous. Discovery of banana plants with B genome non-infective for eBSV opens the way to the introduction of new genitors in programmes of genetic banana improvement.

The Mode of Transmission of Banana streak virus by Paracoccus burnerae (Homiptera; Planococcidae) Vector is Non-circulative

The Mode of Transmission of Banana streak virus by Paracoccus burnerae (Homiptera; Planococcidae) Vector is Non-circulative

Biochemical Characterization of Compatible Plant Virus Interaction: A Case Study with Bunchy Top Virus-Banana Host-Pathosystem

Environmental stresses of both biotic and abiotic nature produce characteristic changes in physiology and metabolic processes of higher plants (Miteva et al., 2005). Among these stresses, infection by the pathogens causes substantial alterations of biochemical changes leading to harmful effects on plant health. Banana cultivation is subjected to many natural calamities including pest and pathogen attacks which constitute the major production problem. Among plant diseases, viral diseases may cause considerable loss on production by retarding plant growth and reducing yield. Four viral diseases viz., Banana Bunchy Top Disease (BBTD) caused by Banana bunchy top virus (BBTV), Bract Mosaic Disease (BBrMD) caused by Banana bract mosaic virus (BBrMV), Banana Streak Disease (BSD) caused by different species of Banana streak virus (BSV) and banana mosaic or infectious chlorosis caused by Cucumber mosaic virus (CMV) occur in most of the banana growing regions of the world. Among banana viral diseases, Banana Bunchy Top Disease (BBTD) is one of the most destructive viral diseases in Tropical Asia, Pacific Indian Oceania (PIO) regions and Africa. Grand Nain, Virupakshi (Hill banana), Robusta, Nendran, Rasthali, Poovan, Ney Poovan, Monthan and Red Banana are severely affected by BBTD. There is no resistance gene source available in germplasm of bananas and plantains (Shekhawat et al., 2012). The BBTV affected plants show intermittent dark green dots, dash, streaks of variable length on leaf sheath, midrib, leaf veins and petioles of infected plants. Leaves produced are progressively shorter, brittle in texture, narrow and gives the appearance of bunchyness at the top leading to 100% yield loss (FAO., 2009). Plants have evolved various pre-existing physical and chemical barriers, as well as inducible defense responses that interfere with pathogen colonization (Jones and Dangl, 2006; Zhao et al., 2008; Vanitha et al., 2009). However, this requires comprehensive studies and understanding of the adaptive mechanisms and responses to BBTV infection in banana. Because viruses cannot be cultured in vitro, our knowledge about their interactions with host and changes on physiology, biochemistry and molecular biology of the host is limited. Moreover, a comprehensive report regarding biochemical alterations in banana plants infected by BBTV is still not clear. Therefore, the present investigation was conducted to find the quantitative estimations of physiological and biochemical parameters such as protein, pigment and carbohydrate contents, phenolic compounds, polyphenol oxidase (PPO), peroxidase (POX), catalase (CAT), ascorbate peroxidise (APX), guaiacol peroxidise (GPX) and superoxide dismutase (SOD) activities, indicating their role in BBTV inoculated and non-inoculated plants of Virupakshi (hill banana), a unique flavoured elite dessert banana cultivar and Grand Nain, which belongs to a Cavendish sub group occupying approximately 50% of area in the world.

Improved methods for the purification and enrichment of banana streak virus for antibody production and protein detection

The purification of viruses from bananas is a complex and laborious process due to the large quantities of polysaccharides and secondary metabolites in the plant tissue. The banana streak viruses (BSVs) are generally difficult to purify to a level that allows generation of high quality antisera. This study presents an improved method of purification of Banana streak MY virus (BSMYV), which allowed us to generate highly specific chicken and rabbit antisera and to detect the capsid proteins for the first time. Finally, we demonstrate further enrichment of BSMYV by isoelectric focusing.

Subpopulation level variation of banana streak viruses in India and common evolution of banana and sugarcane badnaviruses.

Genome sequences of three episomal Banana streak MY virus (BSMYV) isolates sampled from triploid banana hybrids (Chini Champa: AAB; Malbhog: AAB and Monthan: ABB), grown in North-East and South India are reported in this study by sequence-independent improved rolling circle amplification (RCA). RCA coupled with restriction fragment length polymorphism revealed diverse restriction profiles of five BSMYV isolates. Nucleotide substitution rates of BSMYV subpopulation and Banana streak OL virus subpopulation was 7.13 × 10(-3) to 1.59 × 10(-2) and 2.65 × 10(-3) to 5.49 × 10(-3), respectively, for the different coding regions. Analysis of the genetic diversity of banana and sugarcane badnaviruses revealed a total of 32 unique recombination events among banana and sugarcane badnaviruses (inter BSV-SCBV), in addition to the extensive recombination with in banana streak viruses and sugarcane bacilliform viruses (intra-BSV and intra-SCBV). Many unique fragments were shown to contain similar ruminant sequence fragments which indicated the possibility that the two groups of badnaviruses or their ancestors to colonise same host before making the host shift. The distribution of recombination events, hot-spots (intergenic region and C-terminal of ORF3) as well as cold-spots (distributed in ORF3) displayed the mirroring of recombination traces in both group of badnaviruses. These results support the hypothesis of relatedness of banana and sugarcane badnaviruses and the host and geographical shifts that followed the fixation of the species complex appear to be a recent event.

Evaluation of In Vitro Protocols for Elimination of Banana Streak Virus from Tissue Cultured Explants in Banana Seedling Production

The banana industry in Kenya is threatened by the presence of Banana streak virus (BSV). The Jomo Kenyatta University of Agriculture and Technology (JKUAT) commercial banana laboratory uses tissue culture (TC) technique for mass propagation of plantlets which are free from most disease causing organisms for commercial purposes. To evaluate in vitro protocols for production of Banana Streak Virus-free TC banana planting materials for farmers, leaf samples were collected from Thika, Kisii, and JKUAT orchards for indexing. The corms were taken through the TC procedure up to the 2nd subculture stage after which they were subjected to three virus elimination techniques; chemotherapy, meristem tip culture and thermotherapy for evaluation. Indexing for BSV using PCR BSV indicated 90, 80 and 40% infection levels for Kisii, JKUAT and Thika orchards, respectively. For chemotherapy evaluation, concentrations of between 10 and 40 mg/l were used resulting in 0 to 90% virus elimination. For thermotherapy, 27°C (control), 32°C, 34°C, 36°C and 38°C for 10 days, resulted in 0 and 90% virus elimination. Meristem tip culture at 1, 2, 3, 4 and 5mm (control) gave between 0 and 90% virus elimination, respectively. The study indicates that BSV can be eliminated using chemotherapy, thermotherapy and meristem tip culture. Chemotherapy using salicylic acid at 20mg/l can be used to eliminate BSV up 90%. It is also easy to implement since it is incorporated into the medium.

Viral diseases of banana.

Abstract Banana and plantain are important fruit crops grown in the tropical and subtropical regions of the world. Millions of resource-poor people depend on them for their livelihood and food security. These fruit crops are destroyed by several viral diseases causing serious economic losses wherever the crops are cultivated. Here, recent developments on the spread, distribution, biology, diversity, recombination, host range, cutting-edge techniques in diagnostics and comprehensive management of important banana viruses, i.e., banana bunchy top virus (BBTV), banana streak viruses, banana bract mosaic virus and cucumber mosaic virus, as well as minor viruses such as banana mild mosaic virus, are exhaustively reviewed. Due to its high destructive potential, BBTV is regarded as a quarantine pest of very high importance in the banana exporting countries of South and Central America. Using tissue culture technology, it is now possible to control the viruses of banana by adopting virus-free certification programmes in conjunction with exclusion, eradication and adoption of quarantine measures.