Banana-growing Regions Research Articles

Fate of chlordecone in soil food webs in a banana agroecosystem in Martinique

Large quantities of chlordecone-based insecticides were produced and used throughout the world. One of its most important uses was to control the damage caused by Cosmopolites sordidus in banana-growing regions. In the islands of Martinique and Guadeloupe, 18,000 ha of farmland are potentially contaminated. Despite the key role played by soil macrofauna in agroecosystems, there are currently no data on their contamination. The aim of this study was to explore the fate of chlordecone (CLD) and its transfer to different organisms of the soil food web.Seven species of invertebrates representing different taxonomic groups and trophic levels of the soil communities of Martinique were targeted and collected in six experimental banana fields, with a level of contamination within a range of values classically observed. Soil samples and macrofauna from the study sites were analysed for CLD and chlordecol (CLDOH) its main transformation product. The contamination of the soil fauna were related to δ15N (trophic level), proportion of soil ingestion (diet) and types of epidermis (mucus or exoskeleton) in order to study the different mechanisms of macrofauna contamination.Presence of CLD and CLDOH could be quantified in all the soil organisms from contaminated fields. Results showed a significant relationship between the CLD contamination of detritivorous and the ash content of their faeces, suggesting that soil ingestion was the main contamination pathway. In contrast, the exoskeleton-bearing diplopod Trigoniulus coralinus and the soft-bodied earthworm Eudrilus eugeniae, both detritivores with a comparable diet, had similar contamination levels, suggesting that the type of tegument has little influence on bioaccumulation. At the scale of the entire trophic network, a significant relationship was uncovered between δ15N values and CLD contamination of the fauna, therefore providing some in situ evidence for a bioamplification process along the soil food chain.

FocSge1 in Fusarium oxysporum f. sp. cubense race 1 is essential for full virulence

BackgroundFusarium wilt disease of banana is one of the most devastating diseases and was responsible for destroying banana plantations in the late nineteenth century. Fusarium oxysporum f. sp. cubense is the causative agent. Presently, both race 1 and 4 strains of Foc are creating havoc in the major banana-growing regions of the world. There is an urgent need to devise strategies to control this disease; that is possible only after a thorough understanding of the molecular basis of this disease.ResultsThere are a few regulators of Foc pathogenicity which are triggered during this infection, among which Sge1 (Six Gene Expression 1) regulates the expression of effector genes. The protein sequence is conserved in both race 1 and 4 strains of Foc indicating that this gene is vital for pathogenesis. The deletion mutant, FocSge1 displayed poor conidial count, loss of hydrophobicity, reduced pigmentation, decrease in fusaric acid production and pathogenicity as compared to the wild-type and genetically complemented strain. Furthermore, the C-terminal domain of FocSge1 protein is crucial for its activity as deletion of this region results in a knockout-like phenotype.ConclusionThese results indicated that FocSge1 plays a critical role in normal growth and pathogenicity with the C-terminal domain being crucial for its activity.

First Report of Fusarium Wilt Tropical Race 4 in Cavendish Bananas Caused by Fusarium odoratissimum in Colombia

Fusarium wilt of bananas, commonly called Panama disease, is caused by a suite of Fusarium species. Fusarium odoratissimum (previously known as Fusarium oxysporum f.sp. cubense) comprises Tropical Race 4 (TR4) (Maryani et al., 2018), which is highly aggressive on Cavendish bananas as well as many other banana varieties (Ploetz 2015). Since the 1990's TR4 has spread across Asia until it surfaced outside this region in Jordan in 2013 (Garcia-Bastidas et al., 2014). Subsequently, a succession of TR4 incursions in banana-growing regions in Asia, the Middle East, the Indian subcontinent, Africa and even Europe was reported (Zheng et al., 2018). Thus far TR4 was not reported in Latin America. Here, we report the occurrence of TR4 in samples originating from the department of Guajira in the northeast of Colombia, which is one of the leading global banana producing countries (~550.000 ha. banana and plantain production, with 66,000 ha. for export). Typical symptoms, such as wilting and chlorosis of leaves and vascular discoloration, were observed in at least hundred plants in June 2019 in four farms totaling more than 175 ha. This area was placed under quarantine by the Colombian Agricultural Institute (ICA) and a massive eradication effort was started. In total, 22 arbitrarily pseudostem samples were collected from symptomatic Cavendish plants from two farms located 3.8 km apart. These were processed for fungal isolation and characterization as described by Zheng et al. (2018). White fungal colonies developed from surface sterilized (1% NaClO) tissue on potato dextrose agar (PDA). Three single-spore isolates (Col 2, Col 4 and Col 17) that phenotypically resembled F. odoratissimum ( Maryani et al., 2018). Subsequently, these isolates were analyzed using three molecular diagnostics targeting two independent regions of the TR4 genome. The first region was assayed according to Dita et al., (2010) and with the commercial Clear®Detections TR4 kit. The second region was tested with a Loop‐Mediated Isothermal Amplification (LAMP) assay (Ordonez et al., 2019). These tests identified the three isolates as F. odoratissimum TR4 (Figure 1). Further analyses were undertaken by whole-genome sequencing using the Illumina platform (MiSeq Kit V3) and subsequent phylogenetic analyses using the TR4 reference (Foc II5, see PRJNA73539 and PRJNA56513, GenBank) as well as available additional Fusarium spp. (Asai et al., 2019; Ordonez et al., 2015; Maryani et al., 2018; Yun et al., 2019; Zheng et al., 2018). This confirmed that the three Colombian isolates firmly group together with other F. odoratissimum TR4 isolates (Figure 1). Finally, we tested whether the three isolates were able to cause Fusarium wilt in Cavendish. The pathogenicity assays and inoculum production were according to Garcia-Bastidas et al. (2019) and included water controls, a Race 1 isolate, which is not pathogenic on Cavendish, the three Colombian isolates Col 2, Col 4, and Col 17, and the II5 TR4 reference strain. Five plants per isolate were inoculated, all plants inoculated with the Colombian TR4 isolates and the II5 reference showed typical symptoms of Fusarium wilt after four weeks. After six weeks, internal symptoms were recorded (Figure 2), and affected tissue was collected from all plants for re-isolation of the causal fungus. All affected tissues and the re-isolated strains were positive with the aforementioned TR4 diagnostics. No isolates were recovered from water controls or plants inoculated with Race 1, which remained asymptomatic (Figure 2). Taken together, our results confirm the presence of TR4 in Colombia. Despite major efforts currently undertaken to cordon off the affected farms, this is an imminent threat for Colombia and the entire region.

Fermentation optimization and disease suppression ability of a Streptomyces ma. FS-4 from banana rhizosphere soil

BackgroundFusarium wilt of banana is one of the most destructive diseases in banana-growing regions worldwide. Soil-borne diseases and soil microbial communities are closely related. The screening of antagonistic bacteria from soil microorganisms in areas with Fusarium wilt of banana is of great practical significance for controlling this disease.ResultsA strain designated FS-4 was isolated from healthy banana rhizosphere soil in an area affected by Fusarium wilt. This strain exhibited a significant antagonistic effect on the pathogen. Pot experiments revealed that the fermentation broth of strain FS-4 not only decreased the incidence of banana Fusarium wilt, but also promoted the growth of banana seedlings. The strain was identified as Streptomyces ma. by its morphological, physiological, and biochemical characteristics and 16S rRNA gene sequence analysis. The culture and fermentation conditions for this strain were optimized by single-factor and response surface experiments. The optimum culture conditions for Streptomyces ma. FS-4 were as follows: peptone 0.5%, saccharose 2.4, 0.05% K2HPO4, 0.05% MgCl2, and 0.05% NaCl at an initial pH of 7.0; 180 g at 28 °C; and inoculation size of 6% for 62 h. The diameter of bacteriostasis circle for Bacillus subtilis reached 26.7 mm.ConclusionStreptomyces ma. FS-4 is an important microbial resource as a biological agent for the control of plant pathogenic fungi and can be used to promote banana growth.

Status of Pratylenchus coffeae in banana-growing areas of Tanzania

Pratylenchus coffeae is among the plant parasitic nematodes contributing to yield losses of banana. To determine the status of P. coffeae, a survey was conducted in banana-growing regions of Tanzania and samples collected. The results indicated that in 2015 there was an increase in total counts of P. coffeae extracted from roots compared to that reported in 1999 in Unguja West, North and South. Moreover, we noted its presence for the first time in mainland Tanzania. Generally, the densities of P. coffeae were high on banana roots collected at 500–1000 m above sea level. This information on the status of P. coffeae is important in planning management of nematodes in Tanzania.

Emergence of social groups after a biosecurity incursion

This paper examines the formation of social groups in the first 3 months following a significant biosecurity incursion, extending our understanding of a social system in the context of an ongoing emergency response. The broader implications of social change and coping responses post-incursion are a relevant and useful discussion worldwide. Farmers (N = 25) were recruited from three dominant banana-growing regions in North Queensland, Australia. Face-to-face interviews were conducted using a semi-structured format. Key topics covered included perceptions of Panama Tropical Race 4 (TR4), on-farm biosecurity activities, social influences and comparisons, and personal stress. This qualitative approach uses well-known social psychological constructs to help understand and frame farmers’ social behaviours post-incursion. TR4 was perceived as a significant threat by participants; yet, perceptions of vulnerability to TR4 and biosecurity engagement varied. Two dominant social groupings emerged from the data. Active adopters were characterised as proactive and innovative growers, prioritising individual farm protection for the benefit of the broader industry. There was a high level of social support, trust and efficacy, facilitating an adaptive coping style. Passive adopters implemented straightforward and less costly biosecurity measures on farm but were not willing to commit to greater financial or time investments. They expressed an overall wariness towards the biosecurity management process and little trust in authorities. A small sub-group of passive adopters also displayed clear maladaptive coping characteristics (e.g. denial, helplessness) towards TR4, believing that biosecurity action at this point was futile. Proximity to TR4-affected property emerged as having an interactional effect on biosecurity uptake and risk perception. Here, we show for the first time, in situ, the complex social environment post-incursion, indicative of high stress and high uncertainty. Findings can be used on-ground to improve extension engagement and risk communication with growers post-incursion, being mindful there exists a range of coping styles and social influences.

First Report of Fusarium oxysporum f. sp. cubense Tropical Race 4 Associated with Panama Disease of Banana outside Southeast Asia.

Fusarium wilt or Panama disease of banana, caused by Fusarium oxysporum f. sp. cubense (Foc), is among the most destructive plant diseases (3). Race 1 ravaged 'Gros Michel'-based export trades until the cultivar was replaced by resistant Cavendish cultivars. However, a new variant of Foc, tropical race 4 (TR4), was identified in Southeast Asia in 1992 and has spread throughout the region (3). Cavendish clones, which are most important in subsistence and export production, are among the wide range of cultivars that are affected, and there is a huge concern that TR4 will further disseminate in Africa since its presence was announced in November 2013 and move into Latin America, thereby threatening other vital banana-growing regions. In Jordan, Cavendish bananas are produced on 1,000 to 1,500 ha in the Jordan Valley (32°N, 35.5°E). In 2006, symptoms of Fusarium wilt were observed and sampled for the isolation of Foc. On half-strength PDA amended with 100-ppm streptomycin sulfate, pale salmon-colored colonies with floccose mycelia developed consistently from surface-disinfested xylem. Single microconidia from these colonies were transferred to half-strength PDA, and conidia and mycelia from these monospore colonies were stored at -80°C in 15% glycerol. On banana leaf agar (Co60-irradiated leaf tissue on water agar), isolates resembled F. oxysporum phenotypically by producing infrequent three- to five-celled macroconidia, copious, usually aseptate microconida on monophialides, and terminal and intercalary chlamydospores after 2 weeks (2). With nitrate-nonutilizing (nit) mutants and testers for different vegetative compatibility groups (VCGs), each of seven examined monospore isolates were placed in VCG 01213, which contains only strains of TR4 (3). Total DNA was extracted from six isolates and PCR analyses, which confirmed their identity as TR4 (1). Subsequently, one of the isolates (JV11) was analyzed for pathogenicity. Inoculum production and inoculation were according to (1) by dipping (30 min) root-wounded 10-week-old plants of the Cavendish cv. Grand Naine in 2 liters of spore suspension (1.0 × 106 spores/ml). Inoculated plants were then placed in sand in 3-liter pots under 28°C, 70% relative humidity, and a 16/8-h light/darkness photoperiod. Sets of three plants were each treated with either JV11 or two TR4 controls (isolate II-5 and a strain isolated from an affected Cavendish plant in Mindanao, Philippines, both of which were diagnosed as TR4 by PCR and pathogenicity analyses). Control sets were either treated with race 1 originating from Cruz das Almas, Bahia, Brazil (1), or water. After 2 weeks, plants inoculated with JV11 and TR4 controls produced typical symptoms of Fusarium wilt. After 4 weeks, tissue was collected from all plants and plated on Komada's medium. TR4 was directly confirmed by PCR (1), either directly from symptomatic plants (JV11 and TR4 controls), or from isolates that were recovered from these plants. Nothing was re-isolated from race 1 inoculated plants and water controls, which remained asymptomatic. This is the first report of TR4 affecting Cavendish outside Southeast Asia, is its northernmost outbreak, and represents a dangerous expansion of this destructive race. Currently, 80% of the Jordan Valley production area is affected by Fusarium wilt, and 20 to 80% of the plants are affected in different farms.

Direct colony polymerase chain reaction (PCR): An efficient technique to rapidly identify and distinguish Mycosphaerella fijiensis and Mycosphaerella musicola

Sigatoka disease is the most important threat for banana production worldwide. Many species of Mycosphaerella have been described from banana but, to date, the three species Mycosphaerella fijiensis , M. musicola and M. eumusae are the only species found to be pathogenic to banana. Reliable identification by classical methods requires expertise because these fungi produce similar symptoms and they are morphologically similar. For studies of ecology, genetic diversity and epidemiology their differentiation is crucial. Several laboratories have developed molecular protocols to differentiate these fungi. Currently, a number of primers targeting ribosomal sequences, actin, tubulin and histone 3 genes are available for diagnosis of the Sigatoka complex. In the present work, we report a direct colony-polymerase chain reaction (DC-PCR) approach to rapidly distinguish M. fijiensis and M. musicola strains in multiplex PCR reactions. This is the most economical and the fastest procedure reported so far for diagnosis of these two Mycosphaerella species, which are distributed in banana-growing regions in the world; the DC-PCR technique was also found to be amenable for the identification of mating type of M. fijiensis isolates. This DC-PCR may also be applicable to prepare DNA templates for basic PCR-based analyses in other fungi. Keywords: Sigatoka diseases, Banana’s Mycosphaerella , molecular diagnosis, direct colony PCR

Banana bunchy top virus in sub-Saharan Africa: Investigations on virus distribution and diversity

Banana bunchy top virus (BBTV) was first reported from sub-Saharan Africa (SSA) from Democratic Republic of Congo (DRC) in the 1950s, has become invasive and spread into 11 countries in the region. To determine the potential threat of BBTV to the production of bananas and plantains ( Musa spp.) in the sub-region, field surveys were conducted for the presence of banana bunchy top disease (BBTD) in the DRC, Angola, Cameroon, Gabon and Malawi. Using the DNA-S and DNA-R segments of the virus genome, the genetic diversity of BBTV isolates was also determined from these countries relative to virus isolates across the banana-growing regions around the world. The results established that BBTD is widely prevalent in all parts of DRC, Malawi, Angola and Gabon, in south and western part of Cameroon. Analysis of the nucleotide sequences of DNA-S and DNA-R indicate that BBTV isolates from these countries are genetically identical forming a unique clade within the ‘South Pacific’ phylogroup that includes isolates from Australia, Egypt, South Asia and South Pacific. These results imply that farmers’ traditional practice of transferring vegetative propagules within and between countries, together with virus spread by the widely prevalent banana aphid vector, Pentalonia nigronervosa, could have contributed to the geographic expansion of BBTV in SSA. The results provided a baseline to explore sanitary measures and other ‘clean’ plant programs for sustainable management of BBTV and its vector in regions where the disease has already been established and prevent the spread of the virus to as yet unaffected regions in SSA.

First report of corm rot disease caused bySclerotium rolfsiiin banana

A corm rot disease was observed for the first time in banana. The disease was found to occur in the majority of commercial cultivars grown in different banana-growing states of India. The incidence of the disease was up to 50% and found to occur at an altitude up to 3000 m asl. The pathogen was identified as Sclerotium rolfsii based on morphological characters and rDNA internal transcribed spacer sequence data. Bananas (Musa spp.) are the world's fourth most important global food crop grown in more than 120 countries (Molina and Valmayor 1999) and are the staple food for more than 400 million people (Swennen et al. 1995). India is the world's largest banana producer and 26 million tonnes are produced annually from 709 000 ha. However, various pests and disease problems, particularly Fusarium wilt, cause significant losses (Ploetz 2005). During a disease survey in different banana-growing regions of India in March 2005, a new wilt-like disease was observed in cv. Rasthali (Silk-AAB) in the Tirukattupalli area of Thanjavur district in Tamil Nadu, India. The important symptoms observed were yellowing of leaves from base to apex, extensive pseudostem sheath rot with profuse mycelial growth on the pseudostem (Fig. 1A, B). The colour of the rotted portion was yellowish-red to reddish-brown (Fig. 1B, C), with numerous brown sclerotia present. Splitting of the basal portion or the pseudostem sheath was observed, and the bottom leaves had desiccated. The infected plant emanated a mushroom odour. The inner tissues of the corm were spongy and colonised extensively with white mycelium (Fig. 2A). At higher altitudes of 2000-3000 m asl, the cortical portion of the corm was completely converted into a mass of fibre (like coconut fibre) with profuse growth of fungal mycelium (Fig. 2B). In some plants, the infection extended up to half of the medulla region. The emerging peeper was necrotic and colonised extensively with white mycelium. In some cases the mycelial growth was seen on the growing tip of the young bud and resulted in reddish brown necrosis. The symptoms were observed in all stages of plant growth. Samples of the diseased plant parts were collected and brought to the laboratory and cultured on potato dextrose agar (PDA). White mycelial growth was observed within a week. Subsequently, small round dark-brown sclerotia developed in

IS CHEMICAL CONTROL OF MYCOSPHAERELLA FOLIAR DISEASES OF BANANA SUSTAINABLE?

Leaf spot diseases of banana caused by Mycosphaerella musicola or Mycosphaerella fijiensis are the main constraints in commercial plantations in most banana-producing countries. In humid, high-rainfall conditions, plantation production of dessert bananas for export can only be achieved through intensive chemical control. The development of chemical control strategies in Belize, Cameroon and the French West Indies (FWI) over the past 20 years is described. In all of these countries, which are representative of many banana-growing regions, there have been difficulties in terms of the efficacy, cost and environmental impact of chemical control. This is the result of three major factors: (i) the tightening of legislation governing aerial spraying, which is becoming more and more restrictive, especially in the FWI; (ii) the small number of fungicides now approved for leaf spot control; and (iii) the development of resistance to systemic fungicides. In Belize, the intensive use of systemic fungicides over the past 20 years (35-40 applications/year) has led to M. fijiensis developing fungicide resistance. Regular applications (40-45 applications/year) of contact fungicides (mancozeb, chlorothalonil) are now used to control black leaf streak. Although in Cameroon systemic fungicides (12-14 applications/year) were originally used in combination with a forecasting strategy to control black leaf streak, fungicide resistance has developed in commercial plantations, and this has led to regular application of contact fungicides (40-45 applications/year). In Guadeloupe and Martinique, M. musicola has been controlled efficiently through the use of systemic fungicides (5-7 applications/year) in a forecasting strategy for more than 30 years. Recent French legislation limiting aerial spraying and the kind of fungicides that can be used has resulted in the development of fungicide-resistant strains of the pathogen. As a consequence, the number of treatments/year has recently doubled (10-14 applications/year). New alternatives for control are needed. The introduction of fungicides that have less negative environmental effects may be a short-term solution. Organic fungicides or biofungicides applied in mixtures with contact fungicides may allow producers to reduce the amount of active ingredient applied. The possibility of reversing fungicide resistance in order to reintroduce a more sustainable forecasting strategy may be a mid-term solution. The introduction of cultivars bred for resistance is a long-term goal. (Resume d'auteur)

Molecular Typing and Presence of Genetic Markers Among Strains of Banana Finger-Tip Rot Pathogen, Burkholderia cenocepacia, in Taiwan

ABSTRACT Burkholderia cenocepacia (genomovar III of B. cepacia complex), the causal agent of banana finger-tip rot, is a common plant-associated bacterium but also an important opportunistic pathogen of humans. To better understand the nature of B. cenocepacia from banana, the genetic variation among B. cenocepacia isolates from various banana-growing regions in southern Taiwan was examined. Forty-four serial isolates recovered from diseased banana stigmata from three banana-growing regions during the periods ranging from 2002 to 2004 were investigated. All B. cenocepacia isolates picked from quinate-yeast extract tetracycline-polymyxin semiselective medium could cause onion maceration and were polymerase chain reaction (PCR) positive for bcscV, which is a type III secretion gene present in all members of the B. cepacia complex except B. cepacia (formerly genomovar I). Genetic diversity was assessed using recA PCR restriction fragment length polymorphism, recA nucleotide sequence analysis, and pulsed-field gel electrophoresis assays. The assays revealed the genetic variability among the isolates and also allowed us to trace the relationship among isolates. The isolates all were assigned to genomovar III and consisted of two groups, A and B, which corresponded to recA lineage IIIA and IIIB. The group B strains were separated into B1 and B2 subgroups and the B1 strains were further divided into distinct lineages. The B1 strains were the most frequently detected and occurred in all regions tested. There was no significant difference between strains from each subgroup in the virulence on banana fingers of cv. Cavendish. PCR assays were further used to determine whether B. cenocepacia from banana contained the cable pilus subunit gene (cblA), IS1356, and B. cepacia epidemic strain marker (BCESM), which are DNA markers associated with epidemic B. cepacia clinic strains. The results indicated that cblA and IS1356 were absent but the BCESM was found in all isolates. The present study revealed that banana is a natural reservoir of genetically diversified B. cenocepacia strains.

First report of Cladosporium musae on banana in South Africa

An unknown speckle disease was recently observed on Cavendish banana leaves in Levubu, the most northern of the five banana-growing regions of South Africa. Morphological examination of infected material and single conidial isolates of the causal organism revealed that it was Cladosporium musae. Isolates of the fungus were subjected to pathogenicity testing and sequencing of the ITS region (ITS-1 and ITS-2) and the 5.8S gene of the rDNA operon, and compared with an authentic strain of C. musae. These results verified the identity of the fungus as C. musae and constitute the first confirmed report of Cladosporium speckle on banana leaves in South Africa.

Use of infochemicals in Pest Management with Special Reference to the Banana Weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae)

Infochemicals play an important role in the biology of many insect species. An understanding of their role in plant-herbivore-carnivore interactions can be used in the development of tools for the enhancement of environmentally benign alternatives to synthetic pesticides. This review discusses how chemical information mediates ecological interactions between organisms and the role of infochemicals in integrated pest management. Infochemicals can be used in pest monitoring and in pest control, through mating disruption, mass trapping and to aggregate herbivores at delivery sites for biological control agents. Particular emphasis is placed on the potential of using pheromones and kairomones in the management of the banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), a pest in plantations of East African highland banana and plantain in most banana-growing regions of the world. Cosmopolites sordidus produces an aggregation pheromone that attracts both males and females. This pheromone has been identified and synthesised and is being recommended as an effective agent in the trapping and control of the weevil. The synergism between banana plant extracts (kairomones) and the synthetic pheromone in attracting C. sordidus should be better exploited. Future research areas that can provide information for the development of an infochemical-based trapping system for the management of C. sordidus are discussed.

Fusarial wilt of banana in Florida

Fusarium oxysporum f. sp. cubense , recovered from wilted banana plants in Florida, was characterized for pathogenicity on tissue-culture-derived plantlets of race differentials and for vegetative compatibility. Isolates from cv. Bluggoe were identified as race 2 in pathogenicity tests and were compatible with isolates from VCG 0124 which contains members from other banana-growing regions in the eastern and western hemispheres; Florida isolates in this VCG probably originated outside the state. Isolates from cv. Silk were identified as race 1 and were compatible with isolates from VCG 01210, a VCG unique to Florida; their origin is uncertain.