Healthy Banana Plants Research Articles

The aphid Pentalonia nigronervosa (Hemiptera: Aphididae) takes advantage from the quality change in banana plant associated with Banana bunchy top virus infection.

Viral diseases can change plant metabolism, with potential impacts on the quality of the plant's food supply for insect pests, including virus vectors. The banana aphid, Pentalonia nigronervosa Coquerel, is the vector of the Banana bunchy top virus (BBTV), the causal agent of Banana bunchy top disease (BBTD), the most devastating viral disease of bananas in the world. The effect of BBTV on the life-history traits and population dynamics of P. nigronervosa remains poorly understood. We therefore studied the survival rate, longevity, daily fecundity per aphid, tibia length, population growth, and winged morph production of a P. nigronervosa clone grown on healthy or infected, dessert, or plantain banana plants. We found that daily fecundity was higher on infected banana than on healthy banana plants (plantain and dessert), and on plantain than on dessert banana plants (healthy and infected). Survival and longevity were lower on infected dessert bananas than on other types of bananas. In addition, virus infection resulted in a decrease in aphid hind tibia length on both plant genotypes. The survival and fecundity table revealed that the aphid net reproduction rate (Ro) was highest on plantains (especially infected plantain), and the intrinsic growth rate (r) was highest on infected plants. Finally, the increase of aphids and alate production was faster first on infected plantain, then on healthy plantain, and lower on dessert banana (infected and uninfected). Our results reinforce the idea of indirect and plant genotype-dependent manipulation of P. nigronervosa by the BBTV.

Diversity of <i>Fusarium</i> Endophytes Isolated from Wild Bananas in Pandenglang, Indonesia

A group of Fusarium spp., in the Fusarium oxysporum species complex is known as pathogens on bananas, i.e., Fusarium wilt or Panama Disease. However, many Fusarium spp. are also known to be endophytes inside healthy banana plants and have been less explored and investigated. Fusarium endophytes have been demonstrated to be effective against the Fusarium pathogen that causes wilting in some crops such as tomatoes and watermelon. Thus, we explored endophytes Fusarium from local bananas in Pandenglang Banten for further use as biocontrol of Fusarium wilt. Four wild banana accessions were identified, from which 9 Fusarium isolates recovered from its pseudostems asymptomatic plants. All isolates were characterized based on their morphological characters and sequence of the Internal Transcribed Spacer (ITS) gene. These isolates belong to four complexes of Fusarium i.e. Fusarium equiseti species complex, Fusarium oxysporum species complex, Fusarium sambucinum species complex, and Fusarium solani species complex (currently described as Neocosmospora). Further study on molecular characterization of these isolates using specific genes and their potential antagonists of pathogens still needs to be discovered for other use as a biocontrol against Fusarium wilt.

Dynamic analysis of the microbial communities and metabolome of healthy banana rhizosphere soil during one growth cycle.

The banana-growing rhizosphere soil ecosystem is very complex and consists of an entangled network of interactions between banana plants, microbes and soil, so identifying key components in banana production is difficult. Most of the previous studies on these interactions ignore the role of the banana plant. At present, there is no research on the the micro-ecological environment of the banana planting growth cycle. Based on high-throughput sequencing technology and metabolomics technology, this study analyzed the rhizosphere soil microbial community and metabolic dynamics of healthy banana plants during one growth cycle. Assessing the microbial community composition of healthy banana rhizosphere soil, we found that the bacteria with the highest levels were Proteobacteria, Chloroflexi, and Acidobacteria, and the dominant fungi were Ascomycota, Basidiomycota, and Mortierellomycota. The metabolite profile of healthy banana rhizosphere soil showed that sugars, lipids and organic acids were the most abundant, accounting for about 50% of the total metabolites. The correlation network between fungi and metabolites was more complex than that of bacteria and metabolites. In a soil environment with acidic pH, bacterial genera showed a significant negative correlation with pH value, while fungal genera showed no significant negative correlation with pH value. The network interactions between bacteria, between fungi, and between bacteria and fungi were all positively correlated. Healthy banana rhizosphere soil not only has a stable micro-ecology, but also has stable metabolic characteristics. The microorganisms in healthy banana rhizosphere soil have mutually beneficial rather than competitive relationships.

Transmission of Blood Disease in Banana.

Banana Blood disease is a bacterial wilt caused by Ralstonia syzygii subsp. celebesensis and is an economically important disease in Indonesia and Malaysia. Transmission of this pathogen is hypothesized to occur through insects mechanically transferring bacteria from diseased to healthy banana inflorescences and other pathways involving pruning tools, water movement, and root-to-root contact. This study demonstrates that the ooze from the infected male bell and the sap from various symptomatic plant parts are infective, and the cut surfaces of a bunch peduncle, petiole, corm, pseudostem, and the rachis act as infection courts for R. syzygii subsp. celebesensis. In addition, evidence is provided that R.syzygii subsp. celebesensis is highly tool transmissible, that the bacterium can be transferred from the roots of a diseased plant to the roots of a healthy plant and transferred from the mother plant to the sucker. We provide evidence that local dispersal of Blood disease occurs predominantly through mechanical transmission by insects, birds, bats, or human activities from diseased to healthy banana plants and that long-distance dispersal occurs through the movement of contaminated planting material. Disease management strategies to prevent crop losses associated with this emerging disease are discussed based on our findings.

Banana Tree Infected with Banana Bunchy Top Virus Attracts Pentalonia nigronervosa Aphids Through Increased Volatile Organic Compounds Emission.

Banana plants are affected by various viral diseases, among which the most devastating is the "bunchy top", caused by the Banana bunchy top virus (BBTV) and transmitted by the aphid Pentalonia nigronervosa Coquerel. The effect of BBTV on attraction mechanisms of dessert and plantain banana plants on the vector remains far from elucidated. For that, attractiveness tests were carried out using a two columns olfactometer for apterous aphids, and a flight cage experiment for alate aphids. Volatile Organic Compounds (VOCs) emitted by either healthy or BBTV-infected banana plants were identified using a dynamic extraction system and gas-chromatography mass-spectrometry (GC-MS) analysis. Behavioral results revealed a stronger attraction of aphids towards infected banana plants (independently from the variety), and towards the plantain variety (independently from the infection status). GC-MS results revealed that infected bananaplants produced VOCs of the same mixture as healthy bananaplants but in much higher quantities. In addition, VOCs produced by dessert and plantain banana plants were different in nature, and plantains produced higher quantities than dessert banana trees. This work opens interesting opportunities for biological control of P. nigronervosa, for example by luring away the aphid from banana plants through manipulation of olfactory cues.

Can the banana weevil Cosmopolites sordidus be a vector of Fusarium oxysporum f.sp. cubense race 1? Unravelling the internal and external acquisition of effective inoculum.

With the undergoing world outbreak of Fusarium wilt of bananas, it is essential to unravel all the possible process of dissemination of this disease. The host-pest interactions of the banana weevil with banana plants make this insect an important potential vector. This study, carried out in controlled conditions, explores the interaction between the banana weevil and Fusarium oxysporum f.sp. cubense race 1 (Foc), with a focus on the external and internal transport of viable fungal propagules. Viable inoculum of Foc was detected very rapidly on external teguments and in the digestive tract of the insect, i.e. at the lowest time studied of 5min after contact with infected pseudostems. Maximal inoculum acquisition occurred after 1h contact with an inoculum source. External inoculum was higher than the inoculum present in the digestive tract, but external and internal inoculum had the same dynamics. After a contact of an infected source, external and internal inoculum decreased exponentially within 50 h, but weevils remained infested for a long time, as long as 2 or 3 days that would be enough for inoculum dispersal. Viable inoculum was also detected in feces. Foc strains isolated were pathogenic when inoculated to banana plants of the Gros Michel variety but did not provoke any symptom on Cavendish banana plants. These results demonstrate that the infective structures of Foc remain externally viable in the digestive system and the excreta of the banana weevil. Such excreta are capable of making healthy banana plants of the Gros Michel variety. © 2021 Society of Chemical Industry.

Newly isolated strain of Trichoderma asperellum from disease suppressive soil is a potential bio-control agent to suppress Fusarium soil borne fungal phytopathogens

Trichoderma sp. was isolated from the rhizosphere soil of a healthy banana plant grown in a Panama disease-contaminated field (suppressive soil). The selected strain, identified as Trichoderma asperellum, exhibited antifungal activity against four species of phytopathogenic fungi from the Fusarium genus (F. oxysporum, F. fujikuroi, F. tricinctum, F. cantenulatum). Antagonism related mechanisms associated with the T. asperellum isolate against four fungal phytopathogens were studied in vitro both indirectly by the observation of growth competition and directly by antibiosis and mycoparasitism. It was shown that T. asperellum could suppress growth of phytopathogens in the range of 65–74%, as well as inhibits spore germination by 30- 75%. Moreover, T. asperellum was demonstrated to secrete mycolytic enzymes (chitinase and β-1,3, glucanase), which are potentially able to degrade cell walls of the phytopathogens. The observed accumulation of respective transcripts and enzymatic activities of both chitinase and β-1,3, glucanase were remarkably higher in pathogen-induced cultures. The reduction of disease severity by 70% was observed in pot cultures of banana plantlets infected previously with F. oxysporum after 9 weeks of treatment with T. asperellum. Our findings demonstrate that T. asperellum as originated from banana wilt-contaminated plantations express anti-pathogenic effects based on various modes of action, including competitiveness, antibiosis, and mycoparasitism and might be potentially used as a biological control agent to cope with diseases caused by a broad spectrum of pathogenic fungi of Fusarium genus.

Evaluation of Plant Growth Parameters by In vitro and Ex vitro Inoculation of Micropropagated Banana Plantlets with Rhizospheric and Endophytic Bacterial Inoculum

Banana propagation is dependent on propagation by tissue culture for industrial purposes. Due to lack of native endophytes in tissue culture plantlets, reintroduction of beneficial microorganisms to tissue culture plantlets become popular as a useful foundation for improving the level of establishment, increasing plant growth parameters, protecting the plantlets against pest and diseases and overall performance for field plantation. In the present study, rhizospheric and endophytic four bacterial species (Pseudomonas fluorescens, Bacillus putida, Bacillus pumilus, Bacillus amyloliquefaciens were isolated from different parts of healthy banana plants such as root, leaf and pseudostem. Banana tissue culture plantlets were cultured for root formation stage on MS medium and used as host for artificial inoculation. Then, bacterial inoculation was carried out with tissue culture plantlets both in vitro and ex vitro conditions. All banana plantlets used for this experiment were successfully acclimatized and survived in the greenhouse. The experiment consisted of three treatments: (1) bacterial inoculum with in vitro rooted plantlets for 2 weeks (2) bacterial inoculum with ex vitro (hardening) plantlets (3) control with sterilized distilled water. Among these treatments, in vitro inoculation affected significantly increased plant height, number of leaves and plant girth for all data collection times with the highest increment indices: (24.0, 7.0, and 7.3). Ex vitro inoculation showed the second highest increment indices: (22.0, 6.9 and 6.3) for plant height, number of leaves and plant girth, respectively. The lowest number of plant growth parameters were observed in control treatment for all four data collection time (19.0, 6.2, and 6.0). According to the results, application of mixtures of bacterial inoculum was effective for enhanced plant growth parameters of tissue culture banana plantlets under greenhouse condition. In addition, two weeks artificial inoculation during in vitro plantlets stage was found the most suitable method for application of microbes with tissue culture banana plantlets which can promote the microbial rhizosphere of banana prior to field plantation.

EKSPLORASI DAN IDENTIFIKASI TRICHODERMA ENDOFITIK PADA PISANG

Exploration and identification of endophytic Trichoderma in banana. Endophytic fungi Trichoderma is an organism that can used as biocontrol agent. This study aims to isolate and identify endophytic Trichoderma in roots of healthy banana plants from three districts in Yogyakarta, which will be used as biological control agent against the pathogen Fusarium oxysporum f.sp. cubense. Isolation was conducted using TSM (Trichoderma Selective Medium). We obtained six isolates of endophytic Trichoderma spp., i.e., Swn-1, Swn-2, Ksn, Psr-1, Psr-2, and Psr-3. Molecular identification was done by using ITS1 and ITS2 primer pain and sequenced. The sequence of DNA obtained was analysed and compared with NCBI database by using BLAST-N programe. The results showed that all isolates were amplified at 560-bp. Phylogenetic analysis showed that isolates Swn-1, Swn-2 and Psr-1 are homologous to Trichoderma harzianum, isolate Ksn homologous to Trichoderma asperrellum, isolate Psr-2 homologous to Trichoderma gamsii, and isolate Psr-3 homologous to Trichoderma koningiopsis, with the homologous value of 99%.

Members of Gammaproteobacteria as indicator species of healthy banana plants on Fusarium wilt-infested fields in Central America

Culminating in the 1950’s, bananas, the world’s most extensive perennial monoculture, suffered one of the most devastating disease epidemics in history. In Latin America and the Caribbean, Fusarium wilt (FW) caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (FOC), forced the abandonment of the Gros Michel-based export banana industry. Comparative microbiome analyses performed between healthy and diseased Gros Michel plants on FW-infested farms in Nicaragua and Costa Rica revealed significant shifts in the gammaproteobacterial microbiome. Although we found substantial differences in the banana microbiome between both countries and a higher impact of FOC on farms in Costa Rica than in Nicaragua, the composition especially in the endophytic microhabitats was similar and the general microbiome response to FW followed similar rules. Gammaproteobacterial diversity and community members were identified as potential health indicators. Healthy plants revealed an increase in potentially plant-beneficial Pseudomonas and Stenotrophomonas, while diseased plants showed a preferential occurrence of Enterobacteriaceae known for their plant-degrading capacity. Significantly higher microbial rhizosphere diversity found in healthy plants could be indicative of pathogen suppression events preventing or minimizing disease expression. This first study examining banana microbiome shifts caused by FW under natural field conditions opens new perspectives for its biological control.

FIRST REPORT OF FRECKLE DISEASE OF BANANA CAUSED BY PHYLLOSTICTA CAPITALENSIS IN GUANGXI, SOUTHWEST CHINA

In December 2013, irregular spots with gray centers, dark brown edges and chlorotic halos were observed on the old leaves of bananas of cv. Williams (AAA, Cavendish) in Guangxi province (China), with an incidence of 15% to 30%. Small pieces of diseased leaf tissues were surface-sterilized in 75% ethanol for 30 s followed by 2 min in 0.1% HgCl2, rinsed in sterile water, plated on potato dextrose agar (PDA) and incubated at 28oC in darkness. A single-spore culture had initially an olive or dark green mycelium with granular surface and white edges which, over time, turned almost black. Asci containing 8 ascospores, were clavate or cylindrical, stipitate, and measured 35.6-43.6×8.5-10.6 μm. Conidia measured 7.2-11.8×4.0-6.3 μm, and were obpyriform or nearly elliptic. Single spore cultures of the isolate were obtained and used for molecular identification. The internal transcribed spacer (ITS) region of rDNA was amplified and sequenced by utilizing the primers ITS4/ITS5 (2). The ITS region of the isolate (Accession No. LM994823) was 629 bp in length. BLAST analysis of the sequences showed a 99% homology with two Phyllosticta capitalensis isolates (accession Nos KM979840 and JQ743587). Pathogenicity was conducted using healthy banana plants with five or six leaves, approximately 30 cm in height. Nine plants were used for each treatment and three leaves of each plant were artificially inoculated. Mycelial plugs were placed on the surface of the leaves, whereas controls were treated only with agar plugs. All the treated plants were covered with plastic bags for 2 days and incubated at 28oC, 75% relative humidity (RH) and with a 12-h photoperiod. After 7 days, typical lesions identical to those observed on the field-grown plants appeared on the inoculated plants, whereas control plants remained healthy. The re-isolated fungus was identified as P. capitalensis by morphology and molecular analysis. P. capitalensis is generally considered an endophyte or saprophyte, within a wide host range and distributed in different plants (Wulandari et al., 2010; Wong et al., 2012). However, it is a weak plant pathogen which was the causal agent of plant diseases in few cases (Wikee et al., 2013). To our knowledge, this is the first report of P. capitalensis causing freckle disease of banana in China.

A New Approach to Analyzing Endophytic Actinobacterial Population in the Roots of Banana Plants (Musa sp., AAA)

AIM: To elucidate the endophytic actinobacterial populations of healthy banana plant roots. METHODS: A surface sterilization protocol was adopted to remove rhizoplane bacterial DNAs and total DNAs of surface-sterilized roots were purified and analyzed by Illumina-based sequencing. RESULTS and CONCLUSION: A total of 2152102 bacterial sequences remained with an average length of 448bp, 31952 different actinobacterial OTUs at the 97% similarity level were obtained, and the dominant families were Nocardioidaceae, PseudoNocardiaceae and Nocardiaceae, which accounted for 56.37%, 14.36% and 9.77%, respectively. At genus level, Pseudonocardia (11.83%), Rhodococcus (9.74%), Nocardioides (3.06%) were the most abundant taxa. The results indicated that surface sterilization approach with formaldehyde (36%) and Illumina-based sequencing is suitable for analysis of endophytic actinobacterial populations in banana roots.

Plant-growth-promoting traits and antifungal potential of the Bacillus amyloliquefaciens YL-25

Biological control of plant soil-borne diseases has been shown as an attractive and an environment friendly alternative to chemical fungicides. Different microbial strains have been reported effective in controlling plant pathogens. Among those, Bacillus strains have their own importance. Bacillus amyloliquefaciens strain YL-25, isolated from the rhizosphere of healthy banana plant, was evaluated as bio-organic fertiliser (BIO) for its ability to promote plant growth and suppress Fusarium wilt of banana in pot experiment. The results showed that the application of the BIO containing strain YL-25 significantly promoted the growth of banana plants and decreased the incidence of Fusarium wilt compared to the organic fertiliser and chemical fertiliser (CF). In order to explore the beneficial mechanisms of strain YL-25, experiments were conducted in vitro. The phytohormones including indole-3-acetic acid and gibberellin A3 and stable antifungal compounds three homologous of iturin A were identified in the culture broth of strain YL-25. The strain YL-25 also showed the ability to degrade extracellular phytate in plate experiment. Owing to its innate multiple functional traits and biocontrol activity, the strain YL-25 may be used as plant-growth-promoting rhizobacterium and biocontrol agent against Fusarium wilt of banana.

Construction of a heterologous gene expression system in the banana rhizobacterium strain GW-3 and its colonization ability

Rhizobacteria inhabiting the rhizosphere are beneficial to their host plants, and can potentially serve as biocontrol agents to control plant diseases. We isolated the rhizobacterium strain GW-3, which was the dominant bacterium in the rhizosphere soils of healthy banana plants. Then, we constructed an expression system with a kanamycin resistance gene to express a heterologous protein in GW-3. Using the green fluorescent protein gene as the reporter, we monitored expression of the heterologous protein by detecting fluorescence intensity and conducting western blot analyses. The standard fluorescence intensity of the recombinant strain reached 1,482±3.49 RFU. To study the colonization ability of GW-3, we inoculated this bacterium into sterilized and unsterilized rhizosphere soils and monitored the bacterial population over 25days. The populations of GW-3 in rhizosphere soils first increased, then decreased, and finally reached a balance. Laser scanning confocal microscope analyses of fluorescence in banana roots after inoculation with GW-3 confirmed that the recombinant GW-3 strain stably colonized banana root surfaces. Analyses of the bacterial population in unsterilized rhizosphere soils showed that the recombinant GW-3 strain was still the dominant bacterium in banana rhizosphere soils at 25days after inoculation. Together, these results showed that this expression system can be used to express a heterologous protein at high levels in a dominant rhizobacterium. By incorporating relevant resistance genes into the expression system, this method could be used to genetically engineer GW-3 to control banana wilt disease.

Effects of novel bioorganic fertilizer produced by Bacillus amyloliquefaciens W19 on antagonism of Fusarium wilt of banana

Banana production has been severely hindered by the long-term practice of monoculture agriculture. Fusarium wilt, caused by the Fusarium oxysporum f. sp. cubense (FOC), is one of the most destructive diseases that can afflict banana plants. It is both necessary and urgent to find an efficient method for protecting banana production worldwide. In this study, 57 antagonistic bacterial strains were isolated from the rhizospheres of healthy banana plants grown in a heavily wilt-diseased field; of the 57 strains, six strains with the best survival abilities were chosen for further study. Compared with the control and the other strains in the greenhouse experiment, W19 strain was found to observably decrease the incidence of Fusarium wilt and promote the growth of banana plants when combined with the organic fertilizer (OF). This strain was identified as Bacillus amyloliquefaciens based on its morphological, physiological, and biochemical properties, as well as 16S rRNA analysis. Two kinds of antifungal lipopeptides (iturin and bacillomycin D) produced by W19 strain were detected and identified using HPLC–ESI-MS. Another lipopeptide, called surfactin, was also produced by the thick biological film forming W19 strain. In addition to lipopeptides, 18 volatile antifungal compounds with significant antagonistic effect against F. oxysporum were detected and identified using gas chromatography–mass spectrometer (GC–MS). The work described herein not only highlights how the bioorganic fertilizer with B. amyloliquefaciens can be used to control Fusarium wilt of banana but also examines some of the potential mechanisms involved in the biocontrol of Fusarium wilt.

Rapid and sensitive detection of Banana bunchy top virus by loop-mediated isothermal amplification

A sensitive loop-mediated isothermal amplification (LAMP) assay was developed for rapid detection of Banana bunchy top virus (BBTV) infection. The reaction was performed in a single tube at 63°C for 90 min, with an improved closed-tube detection system by adding the SYBR Green I dye to the inside of the tube lid prior to amplification. The detection limit of the LAMP assay was approximately 1 pg/μl plasmid DNA when mixed with extracted DNA from healthy banana plant, and no cross-reaction with other banana-infected pathogens was observed. Real-time turbidimetry was used to monitor the amplification result in the tubes, and it was shown that this LAMP assay was about 100-fold more sensitive than PCR. The results demonstrated that this LAMP method should be useful for both banana disease monitoring and mass propagation of virus-free banana plantlets.

Artificial inoculation of banana tissue culture plantlets with indigenous endophytes originally derived from native banana plants

Fusarium wilt disease of banana is one of the most harmful fungal diseases affecting banana production worldwide. We hypothetically proposed that the loss of indigenous endophytes in tissue culture propagation of banana might be related to increased disease severity on banana plants. In the present study, a mixture of uncultivated endophytes, which was originally derived from native healthy banana plant in plantation, was used to artificially inoculate banana tissue culture plantlets. A broad spectrum of bacterial communities was detected in the roots of artificially inoculated plantlets by 16S ribosomal RNA gene analysis, and γ-Proteobacteria was identified as the dominant group. Banana wilt pathogen Fusarium oxysporum f. sp. cubense race 4 was inoculated to the plantlets after potting to investigate disease progress. With early diagnosis of fungal pathogen infection, 54% reduction was detected in artificially inoculated plantlets compared to endophyte-free control plantlets. The re-introduction of naturally-occurring endophytes into tissue culture banana plantlets led to a 67% suppression rate of wilt disease at the fifth month after pathogen infection on plantlets in the greenhouse. In addition to disease suppression, growth of host plantlets was also promoted with the inoculation of endophytes. The artificial inoculation method provided a foundational understanding of ecological enrichment to control banana wilt disease in future.

Aphid Transmission of Banana Bunchy Top Virus to Bananas After Treatment With a Bananacide

Field and laboratory studies were conducted to determine the impact of using a herbicide as a bananacide on aphid transmission of Banana bunchy top virus (family Nanoviridae, genus Babuvirus, BBTV) to healthy banana (Musa spp.) plants. BBTV-infected banana plants in a commercial orchard were treated with Roundup Weathermax herbicide. Using polymerase chain reaction, the time after herbicide treatment that BBTV could no longer be detected in the infected plants was determined. The impact of the herbicide treatment on Pentalonia nigronervosa Coquerel (Hemiptera: Aphididae) virus acquisition and ability to inoculate healthy banana plants with BBTV also were determined. Generally, banana plants were dead beyond 42 d after herbicide injection (DAI), and BBTV was detected in a similar high percentage of treated plants from 0 up to 21 DAI. During two field trials, 0 and 32% of P. nigronervosa acquired the virus from treated plants at 42 DAI, respectively, but none successfully inoculated a healthy banana plant beyond 35 DAI. Finally, 22% of P. nigronervosa colonies collected directly from the pseudostem of injected plants at the final sample date (42 DAI) tested positive for BBTV and infected 9.5% of the healthy banana plants. The findings indicate that banana plants may remain a potential source of virus inoculum 6 wk after injection with a bananacide. The implications of these findings with respect to BBTV management are discussed.

Effect of endophytic Fusarium oxysporum on root penetration and reproduction of Radopholus similis in tissue culture-derived banana (Musa spp.) plants

AbstractIn Uganda, banana (Musa spp.) production is constrained by the burrowing nematode Radopholus similis. Non-pathogenic, endophytic Fusarium oxysporum has been isolated from healthy banana plants, and several strains have shown potential as biological control agents against R. similis. Plant infection by R. similis can be characterised in three steps: host searching, root penetration and reproduction. In this study, we investigated the effects of three endophytic F. oxysporum strains (Eny1.31i, Eny7.11o and V5w2) on root penetration and reproduction of R. similis in tissue culture-derived banana plants. The number of R. similis that penetrated roots of endophyte-inoculated and untreated plants was not influenced by the endophytes in either laboratory or screenhouse experiments. However, R. similis reproduction was reduced by endophytes. Strain V5w2 gave the greatest suppression of R. similis reproduction. The results of this study imply that antagonism of endophytic F. oxysporum against R. similis in banana plants is post-infectional and mediated through disruption of nematode reproduction.

Isolation and characterization of nonpathogenic Fusarium oxysporum isolates from the rhizosphere of healthy banana plants

One of the most serious diseases of banana is fusarium wilt, caused by Fusarium oxysporum f.sp. cubense (Foc). The objectives of this study were to isolate and identify nonpathogenic F. oxysporum strains from soils suppressive to banana wilt, and to determine the diversity of these isolates. More than 100 Fusarium strains were isolated from the rhizosphere of banana plants and identified to species level. Pathogenicity testing was carried out to confirm that these isolates were nonpathogens of banana. A PCR‐based RFLP analysis of the intergenic spacer region of the ribosomal RNA operon was used to characterize the nonpathogens. The isolates were also compared with isolates of Foc from South Africa and the known biological control isolate of F. oxysporum, Fo47. The species‐specific primers FOF1 and FOR1, in addition to morphological features, were used to confirm the identity of F. oxysporum isolates included in the PCR‐RFLP analysis. Twelve different genotypes could be distinguished, identified by a six‐letter code allocated to each isolate following digestion with the restriction enzymes HaeIII, HhaI, HinfI, MspI, RsaI and ScrfI. Eleven of these included nonpathogenic F. oxysporum isolates, and these groups could all be distinguished from the genotype that included Foc. Fo47 was included in one of the genotype groups consisting of nonpathogenic F. oxysporum isolates from South Africa.