Banana Streak Research Articles

A Four-Partner Plant–Virus Interaction: Enemies Can Also Come from Within

Plant viruses are disseminated by either vertical (vegetative multiplication or sexual reproduction) or horizontal (vector-mediated) propagation. Plant pararetroviruses—members of the Caulimoviridae family—have developed an alternative strategy for vertical propagation via integration within the host plant genome, although integration is not required for viral replication. Integrated endogenous pararetrovirus (EPRV) sequences have undergone extensive viral genome rearrangements and contain more than one copy of the viral genome. Furthermore, EPRV can become infectious upon spontaneous escape of active virus following stresses such as wounding, tissue culture, or interspecific crosses. Such infectious EPRV are of great importance, not only in terms of their ability to precipitate epidemic outbreaks but also because of their effect on breeding of numerous plant genomes in temperate and tropical crops. This is especially true for banana, a crop susceptible to banana streak viruses, the causative agents of banana streak disease. Thus, the classical three-component banana–Banana streak virus (BSV)–mealybug pathosystem can be expanded to include endogenous BSV as an alternative source of active virions. The BSV-banana pathosystem is one of only three pathosystems known to date to harbor this remarkable feature, and the present review focuses exclusively on it to illustrate this four-partner interaction.

INDEXING TISSUE CULTURE BANANA (MUSA SPP.) SEEDLINGS FOR BANANA STREAK VIRUS WITH THE AIM OF ESTABLISHING A CLEAN MOTHER BLOCK

A total of 1137 tissue culture banana (Musa spp.) seedlings were collected between May and July 2007 from nurseries of the Thika National Horticulture Research Centre of the Kenyan Agricultural Research Institute (KARI), Jomo Kenyatta University of Applied Technology and Agro-Genetic Technologies. The seedlings were approximately 3 months old, since potting. Leaf samples from the seedlings were indexed for Banana streak virus (BSV) at KARI-Kabete laboratory. Immuno-capture PCR specific primers to BSV-GF and BSV-Cav were used. Of the 1137 seedlings indexed, 120, 175, 112, 200, 130, 150, 100, 75 and 75 were of cultivar 'Dwarf Chinese' (AAA genome), 'FHIA 18' (AAAB genome), 'Solio' (AAA-EA genome), 'FHIA 17' (AAAA genome), 'Nusu Ng'ombe' (AAA-EA genome), 'Grand Naine' (AAA genome), 'Williams' (AAA genome), 'Uganda Green' (AAA genome) and 'Chinese Cavendish' (AAA genome), respectively. A total of 265 samples from the nine cultivars tested positive for BSV. 'Dwarf Chinese', 'Grand Naine' and 'Williams' cultivars tested positive both for BSV-Cav and BSV-GF. The PCR protocol for detection of BSV was validated. Validation tests were conducted, utilizing fresh banana leaf tissue samples from cultivars 'Lisulya' and 'Khabusi Mboki' (AAA-EA genome), greenhouse tissue cultured plantlets of 'Dwarf Chinese' and 'Ex-Rongai' (AAA genome), a positive control, consisting of freeze-dried banana leaves from Queensland University of Technology (QUT), and a PCR positive control plasmid DNA sample, also from QUT. Extraction of DNA was done using Qiagen DNeasy plant mini kit to generate a DNA template for PCR amplification.

PROTECTING THE AFRICAN BANANA (MUSA SPP.): PROSPECTS AND CHALLENGES

In Africa, bananas (Musa spp.) are staple food crops and sources of income that are cultivated as backyard plantings, mixed-crop plantings and in commercial plantations. Continued production of bananas and plantains, however, is threatened by several important pests and diseases. Nematodes, particularly, are responsible for significant losses across Africa, and the banana weevil (Cosmopolites sordidus) damages both cooking (AAA-EA genome) and dessert bananas (AAA genome). Since its introduction onto the continent, black leaf streak has spread to all African tropical banana production areas, causing immense damage to plantations. Fusarium wilt is important in dessert banana plantings, while Xanthomonas wilt has devastated bananas in Central and Eastern Africa since 2001. Both Banana bunchy top virus and Banana streak viruses occur on the continent. Because of the limited resources available to backyard and mixed-crop growers, many pests and diseases are only partially controlled or not controlled at all, making banana production in Africa highly vulnerable. More importantly, many pests and diseases are indiscreetly disseminated because of limited resources and knowledge. For these reasons, large growing areas have been forced out of further production. Without substantial financial resources, the effect of pests and diseases in Africa can be significantly reduced by promoting the use of clean and healthy planting material, sanitation practices, and quarantine regulations to prevent dissemination of existing pathogens and pests, and the introduction of important foreign pathogens such as Fusarium oxysporum f. sp. cubense 'tropical race 4', and those causing Moko bacterial wilt and Blood bacterial wilt. Two banana breeding programs and several facilities for plant biotechnology already exist in Africa and should be used to develop banana cultivars resistant to pathogens and pests. More importantly, national and regional resources should be pooled in order to ensure sustainable banana production in Africa.

ESTABLISHMENT OF VIRUS-FREE BANANA (MUSA SPP.) MOTHER STOCK FOR PRODUCTION OF CERTIFIED BANANA PLANTS AND BANANA STREAK VIRUS TESTED TISSUE CULTURE SEEDLINGS

ISHS IV International Symposium on Banana: International Conference on Banana and Plantain in Africa: Harnessing International Partnerships to Increase Research Impact ESTABLISHMENT OF VIRUS-FREE BANANA (MUSA SPP.) MOTHER STOCK FOR PRODUCTION OF CERTIFIED BANANA PLANTS AND BANANA STREAK VIRUS TESTED TISSUE CULTURE SEEDLINGS

GROWTH AND YIELD RESPONSE OF THE PLANTAIN (MUSA SPP.) HYBRID 'FHIA 21' TO SHADING AND ROOTING BY INGA EDULIS ON A SOUTHERN CAMEROONIAN ULTISOL

ISHS IV International Symposium on Banana: International Conference on Banana and Plantain in Africa: Harnessing International Partnerships to Increase Research Impact GROWTH AND YIELD RESPONSE OF THE PLANTAIN (MUSA SPP.) HYBRID 'FHIA 21' TO SHADING AND ROOTING BY INGA EDULIS ON A SOUTHERN CAMEROONIAN ULTISOL

Clonagem e purificação de fragmento da proteína capsidial de Banana streak OL virus

O objetivo deste trabalho foi clonar e induzir a expressão de fragmento da proteína capsidial de Banana streak OL virus (BSOLV-CP) em Escherichia coli, bem como purificar a proteína recombinante obtida. Empregou-se um par de iniciadores específicos para amplificar, em PCR, um fragmento de aproximadamente 390 pb, da região codificadora da porção central da BSOLV-CP. O fragmento obtido foi clonado em vetor pGEM-T Easy, subclonado em vetor pQE-30 e transformado em células de E. coli M15 (pREP4) por choque térmico. A expressão da proteína foi induzida por tiogalactopiranosídeo de isopropila (IPTG), e a proteína recombinante BSOLV-rcCP de 14 kDa foi detectada em Western blot e Dot blot. A expressão da proteína BSOLV-rcCP abre novas possibilidades para a obtenção de antígenos para a produção de antissoros contra o BSOLV.

Phylogeny of banana streak virus reveals recent and repetitive endogenization in the genome of its host ( Musa sp.)

Phylogeny of banana streak virus reveals recent and repetitive endogenization in the genome of its host ( Musa sp.)

Banana Streak Disease Survey in Three Plantain Growing Regions of Ghana*

Banana Streak Disease Survey in Three Plantain Growing Regions of Ghana*

Evolution of endogenous sequences of banana streak virus: what can we learn from banana (Musa sp.) evolution?

Endogenous plant pararetroviruses (EPRVs) are viral sequences of the family Caulimoviridae integrated into the nuclear genome of numerous plant species. The ability of some endogenous sequences of Banana streak viruses (eBSVs) in the genome of banana (Musa sp.) to induce infections just like the virus itself was recently demonstrated (P. Gayral et al., J. Virol. 83:6697-6710, 2008). Although eBSVs probably arose from accidental events, infectious eBSVs constitute an extreme case of parasitism, as well as a newly described strategy for vertical virus transmission in plants. We investigated the early evolutionary stages of infectious eBSV for two distinct BSV species-GF (BSGFV) and Imové (BSImV)-through the study of their distribution, insertion polymorphism, and structure evolution among selected banana genotypes representative of the diversity of 60 wild Musa species and genotypes. To do so, the historical frame of host evolution was analyzed by inferring banana phylogeny from two chloroplast regions-matK and trnL-trnF-as well as from the nuclear genome, using 19 microsatellite loci. We demonstrated that both BSV species integrated recently in banana evolution, circa 640,000 years ago. The two infectious eBSVs were subjected to different selective pressures and showed distinct levels of rearrangement within their final structure. In addition, the molecular phylogenies of integrated and nonintegrated BSVs enabled us to establish the phylogenetic origins of eBSGFV and eBSImV.

Micropropagation by tissue culture triggers differential expression of infectious endogenous Banana streak virus sequences (eBSV) present in the B genome of natural and synthetic interspecific banana plantains

The genome of Musa balbisiana spp. contains several infectious endogenous sequences of Banana streak virus (eBSV). We have shown previously that in vitro micropropagation triggers the activation of infectious eBSOLV (endogenous sequences of Banana streak Obino l'Ewai virus) in the synthetic tetraploid interspecific hybrid FHIA21 (AAAB). In this work, we show that another synthetic tetraploid (AAAB) hybrid and two natural triploid (AAB) plantains are equally prone to the activation of infectious eBSOLV during tissue culture. These results are a strong indication that such activation is a general phenomenon in interspecific Musa cultivars, whether synthetic or natural. We also report the first in-depth study of the correlation between the duration of tissue culture and the level of activation of infectious eBSOLV, and show that specific and common activation patterns exist in these banana plants. We hypothesize that these patterns result from the concomitant activation of infectious eBSOLV and a decrease in the virus titre in neoformed plantlets, resulting from cell multiplication outcompeting virus replication. We provide experimental data supporting this hypothesis. No activation of infectious eBSGFV (endogenous sequences of Banana streak Goldfinger virus) by tissue culture was observed in the two natural AAB plantain cultivars studied here, whereas such activation occurred in the AAAB synthetic hybrid studied. We demonstrate that this differential activation does not result from differences in the structure of eBSGFV, as all banana genomes harbour eaBSGFV-7.

Transmission of Cucumber Mosaic Virus (CMV) infecting banana by aphid and mechanical methods

Banana is the premier fruit of the Asia and pacific region. It is the fourth most important food crop after rice, wheat and maize. In Tamil Nadu, banana is grown in 92,200 hectares with an annual production of 48.56 million tones. Among all biotic constraints, viruses cause huge economic loss to the crop. Some of the major diseases are caused by viruses which include Banana Bunchy Top Virus (BBTV), Cucumber Mosaic Virus (CMV), Banana Streak Virus (BSV), Banana Bract Mosaic Virus (BBMV) have been reported in our country. CMV virus concentration in host (Musa) tissue is very less. So it is necessary to transfer this virus to good propagation host such as Nicotiana sp for purification. The purpose of the study was the transmission of CMV infecting banana into propagation host either by aphid or mechanically. The transmission was confirmed through Direct Antigen Coating Enzyme Linked Immuno Sorbent Assay (DAC-ELISA).

Identification of Banana streak virus species Goldfinger, Imové, Mysore and Obino l’Ewaï in Musa spp. in Cuba

Banana streak virus (BSV) species are widespread in Musa spp. They are naturally transmitted by several mealybug species in a semipersistent mode and by activation of endogenous sequences integrated in the genome of Musa balbisiana, one of the progenitors of synthetic and natural hybrids (Dallot et al., 2001). Typical symptoms include yellow streaks on leaves, splitting of the pseudostem and abnormal emergence of the bunch from the middle of the pseudostem, bearing fewer fruits of smaller size (Jones & Lockhart, 1993). Although leaf streaks and pseudostem splitting symptoms have been previously observed in Cuba, BSV species were never identified. Bacilliform particles were observed by immunosorbent electron microscopy in plantain FHIA21 (Font et al., 1998) but the polyclonal antiserum used was raised against several badnavirus species and is therefore not specific to BSV. Given that this virus has never been confirmed in Cuba, field surveys were started in 2007, to study the occurrence, incidence and diversity of BSV species in dessert and cooking banana. Leaf samples were collected nationwide from plants with, and without symptoms, and indexed separately for the four BSV species, Goldfinger (BSGFV), Imové (BSImV), Mysore (BSMysV) and Obino l’Ewaï (BSOLV) by multiplex immunocapture PCR (Le Provost et al., 2006). All four BSV species were detected in several samples each: BSGFV was detected in FHIA25 hybrid (AAB) in Havana, Granma and Pinar del Rio; BSMysV was detected in cv. Yangambi km5 (AAA) in Granma and Santiago de Cuba; BSImV was detected in FHIA25 hybrid in Havana and Pinar del Rio, and in Giant Dwarf Cavendish (AAA) in Ciego de Avila; BSOLV was detected in FHIA18 hybrid (AAAB) in Havana and in FHIA21 hybrid (AAAB) in Havana, Pinar del Rio, Granma, Cienfuegos and Santiago de Cuba. Samples co-infected by species BSGFV and BSImV, were identified in FHIA25 hybrid from Havana and Pinar del Rio whereas samples co-infected by species BSGFV and BSOLV were detected in FHIA21 hybrid from Havana, Pinar del Rio, Granma and Cienfuegos. For each BSV species, a selection of amplification products were cloned and sequenced. The GenBank accession numbers of the sequences reported in this paper are FJ527423–527434. Blast analysis showed that cloned sequences share 96–100% identity with reference sequences AY493509.1 (BSGFV), AB252638.1 (BSImV), AY805074.1 (BSMysV) or AJ002234 (BSOLV). This report presents the first confirmation and identification of BSV species in Cuba. This work was supported by the Guadeloupe Region through its FCR programme and by the French Ministry of Foreign Affairs. Authors are indebted to Professor B.E.L. Lockhart for providing BSV antiserum.

Phylogeny of Banana Streak Virus Reveals Recent and Repetitive Endogenization in the Genome of Its Banana Host (Musa sp.)

Banana streak virus (BSV) is a plant dsDNA pararetrovirus (family Caulimoviridae, genus badnavirus). Although integration is not an essential step in the BSV replication cycle, the nuclear genome of banana (Musa sp.) contains BSV endogenous pararetrovirus sequences (BSV EPRVs). Some BSV EPRVs are infectious by reconstituting a functional viral genome. Recent studies revealed a large molecular diversity of episomal BSV viruses (i.e., nonintegrated) while others focused on BSV EPRV sequences only. In this study, the evolutionary history of badnavirus integration in banana was inferred from phylogenetic relationships between BSV and BSV EPRVs. The relative evolution rates and selective pressures (d(N)/d(S) ratio) were also compared between endogenous and episomal viral sequences. At least 27 recent independent integration events occurred after the divergence of three banana species, indicating that viral integration is a recent and frequent phenomenon. Relaxation of selective pressure on badnaviral sequences that experienced neutral evolution after integration in the plant genome was recorded. Additionally, a significant decrease (35%) in the EPRV evolution rate was observed compared to BSV, reflecting the difference in the evolution rate between episomal dsDNA viruses and plant genome. The comparison of our results with the evolution rate of the Musa genome and other reverse-transcribing viruses suggests that EPRVs play an active role in episomal BSV diversity and evolution.

Cryotherapy of shoot tips: a technique for pathogen eradication to produce healthy planting materials and prepare healthy plant genetic resources for cryopreservation

AbstractCryotherapy of shoot tips is a new method for pathogen eradication based on cryopreservation techniques. Cryopreservation refers to the storage of biological samples at ultra‐low temperature, usually that of liquid nitrogen (−196°C), and is considered as an ideal means for long‐term storage of plant germplasm. In cryotherapy, plant pathogens such as viruses, phytoplasmas and bacteria are eradicated from shoot tips by exposing them briefly to liquid nitrogen. Uneven distribution of viruses and obligate vasculature‐limited microbes in shoot tips allows elimination of the infected cells by injuring them with the cryo‐treatment and regeneration of healthy shoots from the surviving pathogen‐free meristematic cells. Thermotherapy followed by cryotherapy of shoot tips can be used to enhance virus eradication. Cryotherapy of shoot tips is easy to implement. It allows treatment of large numbers of samples and results in a high frequency of pathogen‐free regenerants. Difficulties related to excision and regeneration of small meristems are largely circumvented. To date, severe pathogens in banana (Musa spp.), Citrus spp., grapevine (Vitis vinifera), Prunus spp., raspberry (Rubus idaeus), potato (Solanum tuberosum) and sweet potato (Ipomoea batatas) have been eradicated using cryotherapy. These pathogens include nine viruses (banana streak virus, cucumber mosaic virus, grapevine virus A, plum pox virus, potato leaf roll virus, potato virus Y, raspberry bushy dwarf virus, sweet potato feathery mottle virus and sweet potato chlorotic stunt virus), sweet potato little leaf phytoplasma and Huanglongbing bacterium causing ‘citrus greening’. Cryopreservation protocols have been developed for a wide variety of plant species, including agricultural and horticultural crops and ornamental plants, and can be used as such or adjusted for the purpose of cryotherapy.

HOW TO CONTROL AND PREVENT THE SPREAD OF BANANA STREAK DISEASE WHEN THE ORIGIN COULD BE VIRAL SEQUENCES INTEGRATED IN THE BANANA GENOME?

Banana streak viruses are among the most widely distributed viruses of banana and are responsible for banana streak disease. Natural field spread occurs by either mealybugs or use of infected planting material, such as suckers. Banana streak viruses are pararetroviruses belonging to the genus Badnavirus, in the family Caulimoviridae. Like all members of the Badnavirus genus, they have bacilliform virions, 30 x 150 nm in size and a circular dsDNA genome of 7.4kbp. Fifteen years ago, an increasing number of outbreaks of banana streak disease were reported worldwide. Many occured in banana breeding lines and micropropagated inter-specific banana hybrids. The origin of infections in new hybrids and tissue-cultured plants was linked to the presence of viral DNA sequences integrated into the Musa balbisiana genome. Although integration is not an essential step in the replication cycle of pararetroviruses, it is assumed that under stress conditions some endogenous banana streak viruses could become infectious by reconstituting a complete replication-competent viral genome. Several serological and molecular tools have been developed to detect either virions or endogenous banana streak viruses. They specificity and potential to prevent and control outbreaks of banana streak disease is discussed. (Resume d'auteur)

DETECTION, INCIDENCE AND DIVERSITY OF BANANA STREAK VIRUSES, BANANA MILD MOSAIC VIRUS AND BANANA VIRUS X IN GUADELOUPE

Banana streak viruses (BSVs) infect banana worldwide. BSV sequences present in the genome of Musa balbisiana hamper the detection of cognate episomal viruses by PCR, since PCR results in the amplification of both episomal viral DNA and integrated viral sequences, leading to false positives. A simple single-step multiplex immunocapture PCR (M-IC-PCR) assay was developed for the detection of only episomal BSV. This technique was applied in a study of the occurrence of BSV in Guadeloupe. Leaf samples from the main banana genotypes were indexed for the presence of major BSV species. Although no symptoms could be observed, BSV was found to be common in plantain (AAB), probably as a result of the widespread use of contaminated suckers. In contrast, BSV was uncommon on dessert banana cultivars (AAA), showing that the use of virus-free certified in vitro plants is an efficient strategy for controlling the spread of BSV, and that vector-borne transmission of BSV from plantain to dessert banana is very low in Guadeloupe. Our study also showed that Banana streak GF virus is the most prevalent species in Guadeloupe, with species Banana streak OL virus and Banana streak Mysore virus present at much lower levels. Using the same leaf samples, a study on the occurrence and diversity of Banana virus X (BVX), a member of the Flexiviridae family, which has been recently described and characterised in Guadeloupe, was undertaken. Indexing by direct-binding reverse transcription PCR showed that BVX is very uncommon in Guadeloupe and has a low level of molecular diversity. This is in contrast to Banana mild mosaic virus, which is a closely related member of the Flexiviridae family, and for which an immunocapture reverse transcription nested PCR detection method was established. (Resume d'auteur)

EXPLORING THE BANANA STREAK VIRUSES - MUSA SP. PATHOSYSTEM: HOW DOES IT WORK?

Banana streak viruses (BSVs) are double-stranded DNA pararetroviruses causing banana streak disease. Recently, numerous outbreaks of the disease occurred in many banana-producing areas in interspecific hybrids (#Musa acuminata# × #Musa balbisiana#) originating from virus-free parents. These infections correlated with the presence of endogenous banana streak viruses (eBSVs), viral DNA sequences integrated in the #M. balbisiana# genome only. Although integration is not needed for the viral replication cycle, some viral integrants are infectious under stress conditions by reconstituting a replication-competent genome after possible homologous recombination events. Even though the wild #M. balbisiana# Pisang Klutuk Wulung (PKW) harbours infectious eBSVs, it is resistant to BSVs. We characterised the genetic and genomic endogenous viral organisation of three BSV species in PKW in order to determine the species responsible for the viral expression in the interspecific F1 progeny. (Resume d'auteur)

VIRAL PATHOGENS OF BANANA: OUTSTANDING QUESTIONS AND OPTIONS FOR CONTROL

ISHS III International Symposium on Banana: ISHS-ProMusa Symposium on Recent Advances in Banana Crop Protection for Sustainable Production and Improved Livelihoods VIRAL PATHOGENS OF BANANA: OUTSTANDING QUESTIONS AND OPTIONS FOR CONTROL

Molecular Identification of Banana streak virus Isolates in Kenya

Abstract Banana streak virus (BSV) is a significant constraint to banana production in Kenya. The ability to quickly and reliably detect BSV is important for the management of the virus. Hence, detection of the variability of BSV was necessary for the optimization of a suitable diagnostic protocol to be used for routine screening of tissue cultured material. In this study, 215 potentially infected banana plants from nine major banana growing regions in Kenya were tested for BSV using serological and molecular techniques. Virus particles were detected by immunosorbent electron microscopy (ISEM) in seven of the ten tested samples confirming the presence of BSV. Immuno‐capture‐polymerase chain reaction (IC‐PCR) using a degenerate primer was used on extracted viral DNA and on immune‐captured viral particles from 80 samples. Enzyme‐linked immunosorbent assay (ELISA) confirmed the presence of BSV in 200 samples and IC‐PCR in 38 of the 80 tested samples. A total of 33 sequences were obtained from eight samples by PCR (EMBL accession numbers AM 905900–AM905905) across the conserved reverse transcriptase/RNaseH region of the genome. Pairwise comparison of the sequences suggested that they represented seven different isolates with sequence identity thresholds of 90–100%. Southern blotting and hybridization with a radiolabelled probe of the Lisulya clone, confirmed that both integrated and episomally replicating viral DNA may be present in at least one of the Kenya samples. Therefore, the presence of BSV in Kenya and some diversity within the Kenyan population was confirmed. The diagnostic protocol was optimized for the confirmed isolates.

Construction of bacterial artificial chromosome (BAC) libraries of banana (Musa acuminataandMusa balbisiana)

Le protocole s'applique a la caracterisation de la structure du genome et a l'evolution des genomes de M. acuminata et de M. balbisiana ; a la construction de cartes physiques autour des marqueurs d'interet et des QTLs ; aux etudes de genomique comparative avec d'autre espece de monocotyledones ; a l'etude des modeles d'integration du virus BSV dans les genomes nucleaires de la banane. Le principe, les principaux avantages, le materiel vegetal utilise, le temps necessaire et les resultats attendus sont presentes. Materiel et methodes. Cette partie decrit le materiel de laboratoire necessaire, et les protocoles permettant l'isolement et la lyse des noyaux de cellules de bananier ; la digestion Hind III de ADN a haut poids moleculaire (HPM) et l'analyse electrophorese sur gels a champ pulse ; la digestion Hind III a grande echelle de ADN a HPM et ligation au vecteur pINDIGOBAC-5 ; l'analyse des clones recombinants de BAC. Elle mentionne les principaux problemes pouvant se poser. Resultats. Les protocoles presentes permettent de construire des bibliotheques de BAC a partir d'especes du genre Musa. Ces bibliotheques peuvent etre utilisees pour construire des cartes physiques et selectionner des regions du genome a sequencer. (Resume d'auteur)