Understanding and Biocontrol Management of Panama Disease in Banana Cultivation

Bananas and plantains are both important staple foods and cash crops for millions of people. Bananas are large perennial herbs of the genus Musa. Cultivated bananas are primarily triploids (3x) derived from intraspecific and interspecific crosses of two diploid species Musa acuminata Colla (Ma.) and Musa balbisiana Colla (M.b.) (Simmonds, 1995). In West and Central Africa, plantains provide more than 25% of the carbohydrate requirements for over 70 million people (Vuylsteke et al., 1993). In Uganda, Burundi, and Rwanda, consumption of cooking bananas exceeds 200kg per person per year. The spread of the fungal pathogen Mycosphaerella fijiensis Morelet into Africa has lead to serious declines in the productivity of banana and plantain based farming systems, and lead to the establishment of a plantain breeding program at the International Institute of Tropical Agriculture (HTA) in 1987 (Vuylsteke et al, 1993). Yield losses from fungal pathogens have been the main impetus for the establishment of banana breeding programs throughout the world (Buddenhagen, 1990).The first breeding program was established in 1922 at the Imperial College of Tropical Agriculture (ICTA) in Trinidad to produce dessert bananas resistant to Fusarium oxysporum f. sp. cubense (F. o.c.) the causal agent of Fusarium wilt or Panama disease (Simmonds, 1966). Breeding at ICTA was latter transferred to the Banana Board of Jamaica (BBJ). A second breeding program was established by United Fruit Company in Honduras to breed for resistance to yellow Sigatoka, Mycosphaerella musicola (Mm.), and Fusarium wilt and was later turned over to the Fundacion Hondurefia de Investigacion Agricola (FHIA) (Rowe, 1984).These early breeding efforts have been reviewed by others (Simmonds, 1966; Sheperd, 1974; Stover & Buddenhagen, 1986; Rowe & Rosales, 1990; Ortiz et al, 1995). The past decade has seen the release of cultivars from breeding programs at FHIA, UTA, the Centre de Cooperation Internationale en Recherche Agronomique pour le Development (CERAD), the Centre Regional Bananiers et Plantains (CRBP), the Centro Nacional de Pesquisa de Mandioca Fruticultura of Empresa Brasileira de Pesquisas (CNPMF/EMBRAPA), the Institute Nacional de Investigacion Viandas Tropicales (INIVIT), and the Taiwan Banana Research Institute (TBRI). These cultivars have resistance to Fusarium wilt, black Sigatoka, or yellow Sigatoka, and many have multiple resistances (Rowe & Rosales, 1996). The methods used to produce these cultivars and the “breeding philosophies” behind them vary greatly. This paper will review the methods and philosophies of breeding for fungal resistance in Musa research, and discuss the future of new resistant banana and plantain cultivars and resistance breeding in Musa.

Spot on: managing Panama disease of banana in the Philippines

Fusarium wilt caused by the fungus Fusarium oxysporum f. sp. cubens (Foc) is the most serious disease that attacks banana plants. Salicylic acid (SA) can play a key role in plant-microbe interactions. Our study is the first to examine the role of SA in conferring resistance to Foc TR4 in banana (Musa acuminata L. AAA group, cv. Cavendish), which is the greatest commercial importance cultivar in Musa. We used quantitative real-time reverse polymerase chain reaction (qRT-PCR) to analyze the expression profiles of 45 genes related to SA biosynthesis and downstream signaling pathways in a susceptible banana cultivar (cv. Cavendish) and a resistant banana cultivar (cv. Nongke No. 1) inoculated with Foc TR4. The expression of genes involved in SA biosynthesis and downstream signaling pathways was suppressed in a susceptible cultivar and activated in a resistant cultivar. The SA levels in each treatment arm were measured using high-performance liquid chromatography. SA levels were decreased in the susceptible cultivar and increased in the resistant cultivar. Finally, we examined the contribution of exogenous SA to Foc TR4 resistance in susceptible banana plants. The expression of genes involved in SA biosynthesis and signal transduction pathways as well as SA levels were significantly increased. The results suggest that one reason for banana susceptibility to Foc TR4 is that expression of genes involved in SA biosynthesis and SA levels are suppressed and that the induced resistance observed in banana against Foc TR4 might be a case of salicylic acid-dependent systemic acquired resistance.

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.

1,8-Cineole: An attractant for the banana weevil, Cosmopolites sordidus

Banana production is seriously threatened by Fusarium wilt (FW), a disease caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc). In the mid-twentieth century FW, also known as “Panama disease”, wiped out the Gros Michel banana industry in Central America. The devastation caused by Foc race 1 was mitigated by a shift to resistant Cavendish cultivars, which are currently the source of 99% of banana exports. However, a new strain of Foc, the tropical race 4 (TR4), attacks Cavendish clones and a diverse range of other banana varieties. Foc TR4 has been restricted to East and parts of Southeast Asia for more than 20 years, but since 2010 the disease has spread westward into five additional countries in Southeast and South Asia (Vietnam, Laos, Myanmar, India, and Pakistan) and at the transcontinental level into the Middle East (Oman, Jordan, Lebanon, and Israel) and Africa (Mozambique). The spread of Foc TR4 is of great concern due to the limited knowledge about key aspects of disease epidemiology and the lack of effective management models, including resistant varieties and soil management approaches. In this review we summarize the current knowledge on the epidemiology of FW of banana, highlighting knowledge gaps in pathogen survival and dispersal, factors driving disease intensity, soil and plant microbiome and the dynamics of the disease. Comparisons with FW in other crops were also made to indicate possible differences and commonalities. Our current understanding of the role of main biotic and abiotic factors on disease intensity is reviewed, highlighting research needs and futures directions. Finally, a set of practices and their impact on disease intensity are discussed and proposed as an integrative management approach that could eventually be used by a range of users, including plant protection organizations, researchers, extension workers and growers.

Globally, the production of bananas (Musa sp. L.) often suffers from various environmental challenges. Among them, biotic stress-induced disease caused by phytopathogenic soil microorganisms is the most threatening factor. Fusarium oxysporum f. sp. cubense Foc Tropical Race 4 (Foc-TR4) is an important soil-borne fungus triggering the severe disease, Fusarium wilt (Panama disease) in bananas. Following infection in a wide variety of bananas, strain Foc-TR4 harshly reduced their cultivation. Herein, we have summarized the present scenario of Fusarium wilt disease. Numerous challenges have been proposed by researchers to control the Panama disease as well as to improve banana production. Primarily aiming at increasing disease tolerance to bananas and improving their cultivation, various management strategies like crop rotation, burning of rice husks, biological soil disinfection, and use of chemical fungicides have been developed. However, these chemical and cultural practices have several drawbacks and therefore not often used. Plant growth-promoting (PGP) bacteria offer one of the most environmentally friendly, effective, safe, and economically sound solution to combat the Panama disease. Apart from growth promotion, this PGPR prevents phyto-pathogen-induced diseases. The recent chapter highlights the utilization of beneficial and antagonistic PGPR and their efficacy against diseases, and bacterial-mediated mechanisms involved in managing Panama disease. Induced systemic resistance (ISR), production of antibiotics, extracellular enzymes, cyanogenic compounds, siderophores, and other antifungal metabolites are the main mechanisms involved in PGPR-induced disease suppression. It will be possible to build or select sustainable management techniques to prevent or aid to minimize Fusarium wilt incidence in banana plantations using the scientific knowledge gathered in this research. The use of indigenous PGP rhizobacteria in plant disease control is gaining popularity as environmental and health concerns underscore the need for a more sustainable agriculture system.

Fusarium wilt (Panama disease) of bananas is well established in two of the five banana production regions in South Africa: Kiepersol (near Hazyview) and southern KwaZulu-Natal. The disease is caused by a soilborne fungus, Fusarium oxysporumSchlechtend.: Fr. f. sp. cubense (E.F. Sm.) W.C. Snyd. & H.N. Hans., which is most commonly introduced into an area by infected plant material or in contaminated soil attached to vehicles, farm machinery, or footwear. In September 2000, banana plants were observed dying at an experimental site in a commercial Cavendish plantation in the Tzaneen area of the Northern Province of South Africa. Symptoms included wilting of leaves (starting from the oldest foliage) and yellow-brown discoloration of vascular tissue in the rhizome and pseudostem. These symptoms are typical of those described for Panama disease of bananas (2). Similar symptoms were observed at another experimental site in a banana plantation in the Komatipoort region of the Mpumalanga Province in November 2000. Komatipoort is currently the largest banana production region in South Africa. Panama disease has not previously been reported in the Tzaneen and Komatipoort regions. Both are at least 200 km away from the other banana production areas in South Africa. Fungal isolations were made from four diseased plants in both Tzaneen and Komatipoort, and the discolored tissue of the pseudostem was placed on potato dextrose agar amended with novobiocin (0.2 g/liter). Single-spore cultures made from developing colonies were identified as F. oxysporum based on morphological characteristics. Isolates were sent to the Cooperative Research Centre for Tropical Plant Protection (CRCTPP) in Australia for identification by means of DNA amplification fingerprinting (DAF) analysis (1). Based on DAF analysis, isolates from Tzaneen and Komatipoort were identical to those in vegetative compatibility group 0120 of F. oxysporum f. sp. cubense ("subtropical" race 4), the causal agent of Panama disease in Kiepersol and southern KwaZulu-Natal. Pathogenicity studies were performed in the greenhouse by inoculating 5-cm Cavendish banana plants with two isolates of F. oxysporum f. sp. cubense from Tzaneen and two isolates from Komatipoort. Ten plants per isolate were inoculated by submerging their roots in a suspension of microconidia (105 spores/ml). Roots of control plants were submerged in sterile distilled water. Within 6 weeks, wilting symptoms developed on the lower leaves of inoculated banana plants, and the central cylinder of the rhizomes turned reddish brown. F. oxysporum f. sp. cubense was reisolated from the diseased tissue to complete Koch's postulates. The outbreaks of Panama disease in Komatipoort and Tzaneen do not appear to have spread further. Both of the infected fields were placed under quarantine, and symptomatic plants were destroyed.

A range of basidiomycetes including the edible mushroom Pleurotus ostreatus (Po) can suppress plant pathogens such as Fusarium spp. With the current increase in production and consumption of Po in Uganda, the spent Po substrate (SPoS) could be an alternative to manage Fusarium wilt of banana (FWB), caused by the soil borne pathogen Fusarium oxysporum f. sp. cubense, race 1 (Foc). This study determined the potential of SPoS to inhibit Foc in vitro and in potted plants. In vitro studies confirmed suppression of Foc in pure co-culture (Po vs. Foc) assays and media amended with different concentrations (0% to 50% w/v) of un-sterilized SPoS filtrates. Foc growth in the sterile SPoS filtrate was comparable to the water control, suggesting possible roles of biotic or thermolabile components of the SPoS. To further verify the suppressive effects of SPoS, pot experiments were carried out with a resistant (‘Mbwazirume’, AAA) and susceptible (‘Sukali Ndizi’, AAB) banana cultivar using both artificially and naturally infested soils. Independent of the inoculation method, SPoS significantly reduced the severity of FWB in pot experiments. Susceptible cultivar ‘Sukali Ndizi’ growing in substrates amended with SPoS showed lower (1.25) corm damage (Scale 0–5) than the un-amended control (3.75). No corm damage was observed in uninoculated controls. The resistant cultivar ‘Mbwazirume’, showed slight (0.25) corm damage only in the Foc-inoculated plants without SPoS. These findings suggest that SPoS could be used as part of the management practices to reduce the impact of FWB.

Panama disease of banana, caused by the fungus Fusarium oxysporum f. sp. cubense, is a serious constraint both to the commercial production of banana and cultivation for subsistence agriculture. Previous work has indicated that F. oxysporum f. sp. cubense consists of several clonal lineages that may be genetically distant. In this study we tested whether lineages of the Panama disease pathogen have a monophyletic origin by comparing DNA sequences of nuclear and mitochondrial genes. DNA sequences were obtained for translation elongation factor 1alpha and the mitochondrial small subunit ribosomal RNA genes for F. oxysporum strains from banana, pathogenic strains from other hosts and putatively nonpathogenic isolates of F. oxysporum. Cladograms for the two genes were highly concordant and a partition-homogeneity test indicated the two datasets could be combined. The tree inferred from the combined dataset resolved five lineages corresponding to "F. oxysporum f. sp. cubense" with a large dichotomy between two taxa represented by strains most commonly isolated from bananas with Panama disease. The results also demonstrate that the latter two taxa have significantly different chromosome numbers. F. oxysporum isolates collected as nonpathogenic or pathogenic to other hosts that have very similar or identical elongation factor 1alpha and mitochondrial small subunit genotypes as banana pathogens were shown to cause little or no disease on banana. Taken together, these results indicate Panama disease of banana is caused by fungi with independent evolutionary origins.

Banana is a major tropical fruit crop but banana production worldwide is seriously threatened due to Fusarium wilt. Fusarium oxysporum f. sp. cubense (Foc), the causal agent of Fusarium wilt of banana (also referred as Panama disease) is an asexual, soil inhabiting facultative parasite. Foc isolates can be classified into three races that are not defined genetically, but for their pathogenicity to different banana cultivars. Despite mycotoxins being some of the best studied virulence factors of phytopathogenic fungi and these have been useful for the prediction of Foc virulence on banana plants, toxins produced by Foc race 2 strains have not been previously identified. The aim of this contribution was to identify the phytotoxic metabolites closely related to banana wilt caused by a Foc race 2 strain. We used an in vitro bioassay on detached banana leaves to evaluate the specificity of the microbial culture filtrates before a partial purification and further identification of Foc race 2 phytotoxins. A 29-day-old host-specific culture filtrate was obtained but specificity of culture filtrate was unrecovered after partial purification. The non-specific phytotoxins were characterized as fusaric acid, beauvericin, and enniatin A. Whereas some, if not all, of these phytotoxins are important virulence factors, a proteinaceous fraction from the specific 29-day-old culture filtrate protected the leaves of the resistant banana cultivar from damage caused by such phytotoxic metabolites.

Silicon in banana plants: uptake, distribution and interaction with the disease fusarium wilt

Panama disease caused by Fusarium oxysporum f. sp. cubense infection on banana is devastating banana plantations worldwide. Biological control has been proposed to suppress Panama disease, though the stability and survival of bio-control microorganisms in field setting is largely unknown. In order to develop a bio-control strategy for this disease, 16S rRNA gene sequencing was used to assess the microbial community of a disease-suppressive soil. Bacillus was identified as the dominant bacterial group in the suppressive soil. For this reason, B. amyloliquefaciens NJN-6 isolated from the suppressive soil was selected as a potential bio-control agent. A bioorganic fertilizer (BIO), formulated by combining this isolate with compost, was applied in nursery pots to assess the bio-control of Panama disease. Results showed that BIO significantly decreased disease incidence by 68.5%, resulting in a doubled yield. Moreover, bacterial community structure was significantly correlated to disease incidence and yield and Bacillus colonization was negatively correlated with pathogen abundance and disease incidence, but positively correlated to yield. In total, the application of BIO altered the rhizo-bacterial community by establishing beneficial strains that dominated the microbial community and decreased pathogen colonization in the banana rhizosphere, which plays an important role in the management of Panama disease.

Panama disease caused by Fusarium oxysporum f. sp. cubense infection on banana is devastating banana plantations worldwide. Biological control has been proposed to suppress Panama disease, though the stability and survival of bio-control microorganisms in field setting is largely unknown. In order to develop a bio-control strategy for this disease, 16S rRNA gene sequencing was used to assess the microbial community of a disease-suppressive soil. Bacillus was identified as the dominant bacterial group in the suppressive soil. For this reason, B. amyloliquefaciens NJN-6 isolated from the suppressive soil was selected as a potential bio-control agent. A bioorganic fertilizer (BIO), formulated by combining this isolate with compost, was applied in nursery pots to assess the bio-control of Panama disease. Results showed that BIO significantly decreased disease incidence by 68.5%, resulting in a doubled yield. Moreover, bacterial community structure was significantly correlated to disease incidence and yield and Bacillus colonization was negatively correlated with pathogen abundance and disease incidence, but positively correlated to yield. In total, the application of BIO altered the rhizo-bacterial community by establishing beneficial strains that dominated the microbial community and decreased pathogen colonization in the banana rhizosphere, which plays an important role in the management of Panama disease.

Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc) is one of the most destructive diseases of banana. Methods to control the disease are still inadequate. The present investigation targeted expression of defense-related genes in tissue cultured banana plantlets of Fusarium resistant and susceptible cultivars after infection with biological control agents (BCAs) and Fusarium (Foc race 1). In total 3034 differentially expressed genes were identified which annotated to 58 transcriptional families (TF). TF families such as MYB, bHLH and NAC TFs were mostly up-regulated in response to pathogen stress, whereas AP2/EREBP were mostly down-regulated. Most genes were associated with plant–pathogen response, plant hormone signal transduction, starch and sucrose metabolism, cysteine and methionine metabolism, flavonoid biosynthesis, selenocompound metabolism, phenylpropanoid biosynthesis, mRNA surveillance pathway, mannose type O-glycan biosynthesis, amino acid and nucleotide sugar metabolism, cyanoamino acid metabolism, and hormone signal transduction. Our results showed that the defense mechanisms of resistant and susceptible banana cultivars treated with BCAs, were regulated by differentially expressed genes in various categories of defense pathways. Furthermore, the association with different resistant levels might serve as a strong foundation for the control of Fusarium wilt of banana.