Evaluation of legume intercrops on the population dynamics and damage level of burrowing nematode (Radopholus similis) in banana (Musa spp.)

Radopholus similis is the most destructive plant parasitic nematode in banana production systems. A glasshouse experiment was carried out to evaluate the effect of legume intercrops on R. similis population and damage level in banana. A trial was laid out in a randomised complete block design with five treatments and five replications. The treatments were banana/cowpea (Vigna unguiculata) intercrop, banana/sunn hemp (Crotalaria juncea) intercrop, sole banana, sole banana with nematicide (Fenamiphos) and sole cowpea. Sunn hemp intercrop was suppressing R. similis population densities and reduced banana root damage the most compared to tested treatments. The legume intercropped banana plants had a significantly higher fresh root mass as the sole-cropped banana with nematicide while the sole-cropped banana without nematicide had significantly lowest fresh root mass. Sunn hemp and cowpea legumes are recommended for adoption by smallholder banana farmers as alternatives to nematicide use.     

The development of plant-parasitic nematode infestations on micro-propagated banana plants following field control measures in Côte d'Ivoire

Of the weeds that were found in banana production areas, only Asystasia gangetica was parasitised by Radopholus similis; Helicotylenchus multicinctus and Hoplolaimus pararobustus were able to parasitise all weed species. Field trials were carried out in Cote d'Ivoire to assess the potential for using nematode-free micro-propagated banana plants following cultural and chemical methods for nematode control. Banana (Musa acuminata) cv. Poyo was examined for nematodes after weed fallow, flooding and chemical treatment. Before replanting bananas, nematode assays showed that: i) all nematode species declined but were not eliminated after a 1,3-dichloropropene soil treatment; ii) H. multicinctus, H. pararobustus and Cephalenchus emarginatus were still present after either a 2-year weed fallow (dominated by Chromolaena odorata or Asystasia gangetica) or a 10-week flooding; iii) R. similis did not persist after fallowing or flooding. All nematode species were found in plots treated with 1,3-dichloropropene and that had been planted with bullheads, suckers or nematode-free micropropagated plants. After both fallow and flooding, R. similis was reintroduced on infested planting materials (bullheads and suckers) even when they were pre-treated with a nematicide. When fallow and flooded plots were planted with nematode-free materials (vitro-plants), R. similis did not appear in the roots for two vegetative cycles. The other species, still present in the soil, invaded the roots and increased slowly in numbers. These results were confirmed in commercial banana plantations.     

Generation of transgenic plantain (Musa spp.) with resistance to plant pathogenic nematodes

Plant parasitic nematodes impose a severe constraint on plantain and banana productivity; however, the sterile nature of many cultivars precludes conventional breeding for resistance. Transgenic plantain cv. Gonja manjaya (Musa AAB) plants, expressing a maize cystatin that inhibits nematode digestive cysteine proteinases and a synthetic peptide that disrupts nematode chemoreception, were assessed for their ability to resist nematode infection. Lines were generated that expressed each gene singly or both together in a stacked defence. Nematode challenge with a single species or a mixed population identified 10 lines with significant resistance. The best level of resistance achieved against the major pest species Radopholus similis was 84% ± 8% for the cystatin, 66% ± 14% for the peptide and 70% ± 6% for the dual defence. In the mixed population, trial resistance was also demonstrated to Helicotylenchus multicinctus. A fluorescently labelled form of the chemodisruptive peptide underwent retrograde transport along certain sensory dendrites of R. similis as required to disrupt chemoreception. The peptide was degraded after 30 min in simulated intestinal fluid or boiling water and after 1 h in nonsterile soil. In silico sequence analysis suggests that the peptide is not a mammalian antigen. This work establishes the mode of action of a novel nematode defence, develops the evidence for its safe and effective deployment against multiple nematode species and identifies transgenic plantain lines with a high level of resistance for a proposed field trial.     

A comparative study of the reproductive fitness and pathogenicity of a population of Radopholus similis from Davao,Philippines, on banana (Musa spp.)

The in vitro reproductive fitness on carrot discs and the in vivo pathogenicity on selected FHIA (Fundación Hondureña de Investigaciónes Agrícola) banana hybrids of a population of Radopholus similis isolated from banana in Davao, Philippines, were investigated at the Bureau of Plant Industry, Davao City, Philippines. It was shown that on carrot discs following inoculation with 25 females, the Davao population had the highest population density and multiplication rate compared with two other R. similis populations from the Philippines (Los Baños and Quezon) and two exotic populations of R. similis (from Uganda and Indonesia). According to the Gompertz model, the Davao population also had a short lag phase and a high maximum specific growth. Following inoculation with one single female, the Davao population also had the highest multiplication rate and the highest proportion of juveniles and females compared with the other four populations included in the experiments. Nine weeks after inoculation with 1000 vermiforms, the R. similis population from Davao had reduced the plant height of the FHIA hybrids included in the experiment (FHIA-3, FHIA-4, FHIA-5, FHIA-18 and FHIA-23) on average by 37%, plant girth by 5.3–40.9%, shoot weight by 20.1–65.8% and root weight by 31.7–69.7%, indicating the high pathogenicity of this population on banana. FHIA-4 was tolerant to R. similis infection.     

Quantitative Digital Imaging of Banana Growth Suppression by Plant Parasitic Nematodes

A digital camera fitted with a hemispherical lens was used to generate canopy leaf area index (LAI) values for a banana (Musa spp.) field trial with the aim of establishing a method for monitoring stresses on tall crop plants. The trial in Uganda consisted of two cultivars susceptible to nematodes, a plantain, Gonja manjaya and an East African Highland banana, Mbwazirume, plus a nematode resistant dessert banana, Yangambi km5. A comparative approach included adding a mixed population of Radopholus similis, Helicotylenchus multicinctus and Meloidogyne spp. to the soil around half the plants of each cultivar prior to field planting. Measurements of LAI were made fortnightly from 106 days post-planting over two successive cropping cycles. The highest mean LAI during the first cycle for Gonja manjaya was suppressed to 74.8±3.5% by the addition of nematodes, while for Mbwazirume the values were reduced to 71.1±1.9%. During the second cycle these values were 69.2±2.2% and 72.2±2.7%, respectively. Reductions in LAI values were validated as due to the biotic stress by assessing nematode numbers in roots and the necrosis they caused at each of two harvests and the relationship is described. Yield losses, including a component due to toppled plants, were 35.3% and 55.3% for Gonja manjaya and 31.4% and 55.8% for Mbwazirume, at first and second harvests respectively. Yangambi km5 showed no decrease in LAI and yield in the presence of nematodes at both harvests. LAI estimated by hemispherical photography provided a rapid basis for detecting biotic growth checks by nematodes on bananas, and demonstrated the potential of the approach for studies of growth checks to other tall crop plants caused by biotic or abiotic stresses.     

Relative mycorrhizal dependency and mycorrhiza-nematode interaction in banana cultivars (Musa spp.) differing in nematode susceptibility

Four Musa cultivars, differing in nematode susceptibility, were selected to study their relative mycorrhizal dependency and to study the interaction between the arbuscular mycorrhizal fungus (AMF), Glomus mosseae, and two migratory endoparasitic nematodes, Radopholus similis and Pratylenchus coffeae. Mycorrhization with G. mosseae resulted in significantly better plant growth, even in the presence of R. similis and P. coffeae. No differences in relative mycorrhizal dependency (RMD) were observed among the four cultivars. G. mosseae suppressed nematode population build-up in Grande Naine and Pisang Jari Buaya. Only in the case of R. similis (Indonesian population) in Pisang Jari Buaya, no significant suppression was observed. In the case of P. coffeae, the AMF reduced the damage in the roots, caused by the nematodes. For R. similis, no reduction of damage was observed. In all, except one experiment, the frequency of the mycorrhizal colonisation was negatively affected by the nematodes.     

Potential of Foliar,Dip, and Injection Applications of Avermectins for Control of Plant-Parasitic Nematodes

Studies were conducted to determine the potential of two avermectin compounds, abamectin and emamectin benzoate, for controlling plant-parasitic nematodes when applied by three methods: foliar spray, root dip, and pseudostem injection. Experiments were conducted against Meloidogyne incognita on tomato, M. javanica on banana, and Radopholus similis on banana. Foliar applications of both avermectins to banana and tomato were not effective for controlling any of the nematodes evaluated. Root dips of banana and tomato were moderately effective for controlling M. incognita on tomato and R. similis on banana. Injections (1 ml) of avermectins into banana pseudostems were effective for controlling M. javanica and R similis, and were comparable to control achieved with a conventional chemical nematicide, fenamiphos. Injections of 125 to 2,000 μg/plant effectively controlled one or both nematodes on banana; abamectin was more effective than emamectin benzoate for controlling nematodes.     

Banana Rhizodeposition: Characterization of Root Border Cell Production and Effects on Chemotaxis and Motility of the Parasitic Nematode Radopholus similis

Rhizodeposition was collected from root tips of banana (Musa acuminata). Two varieties, Grande naine and Yangambi km5, susceptible and resistant towards the burrowing nematode Radopholus similis, respectively, were examined for root border cell production under in vitro and in soil growing conditions. Two types of cells were observed in rhizodeposition: spherical cells containing large amyloplasts, called statocytes (8% of total), and long ellipsoidal border cells (92%). Border cell production was high, related to root length and not different between the two cultivars. Rhizodeposition from plants grown in soil contained similar amounts of border cells, but viability was lower than in in vitro grown plants. Chemotaxis and motility assays were performed to test the effects of banana roots, roots without rhizodeposition, rhizodeposition, exudates and border cells on the behaviour of R. similis. Roots of both the susceptible and resistant variety attracted R. similis, but only in the presence of rhizodeposition. Isolated rhizodeposition of Yangambi km5 also attracted nematodes. Border cells and exudates did not affect nematode chemotaxis. Roots of both varieties induced quiescence in R. similis in the chemotaxis assay. Thirty to fifty percent of the nematodes became temporary quiescent in the motility assay with rhizodeposition and exudates. The effect lasted for 24 h for Grande naine and up to 3 days for Yangambi km5. Rhizodeposition collected from plants grown in soil affected neither R. similis chemotaxis nor motility. Overall, there were no indications that rhizodeposition is involved in preformed resistance against R. similis in Yangambi km5.     

Effect of Endophytic Fusarium oxysporum on Host Preference of Radopholus similis to Tissue Culture Banana Plants

The burrowing nematode Radopholus similis is one of the major constraints to banana (Musa spp.) production worldwide. Resource-poor farmers can potentially manage R. similis by using naturally occurring banana endophytes, such as nonpathogenic Fusarium oxysporum, that are inoculated into tissue culture banana plantlets. At present, it is unclear at what stage in the R. similis infection process the endophytes are most effective. In this study, the effect of three endophytic F. oxysporum isolates (V5w2, Eny1.31i and Eny7.11o) on R. similis host preference of either endophyte-treated or untreated banana plants was investigated. No differences were observed between the proportion of nematodes attracted to either root segments excised from endophyte-treated or untreated plants, or in experiments using endophyte-treated and untreated tissue culture banana plantlets. These results imply that the early processes of banana plant host recognition by R. similis are not affected by endophyte infection.     

Support for the ‘out-of-Southeast Asia’ hypothesis for the origin of Australian populations of <Emphasis Type="Italic">Radopholus similis</Emphasis> (Cobb, 1893) (Nematoda: Pratylenchidae)

Radopholus similis is one of the world’s ten most economically important plant-parasitic nematodes. It is especially a problem in banana cultivation, where the nematodes’ feeding reduces yields and causes toppling disease. It has been suggested that the genus Radopholus Thorne, 1949 might have an Australian origin, but the native range of R. similis (Cobb, 1893) is not well known. Here we undertake a phylogeographical study of samples of R. similis from banana plantations down the eastern seaboard of Australia, with additional samples from Costa Rica and accessions from GenBank, to examine the origin of pest populations of R. similis. The lack of genetic diversity of R. similis within Australia, and its sharing of a worldwide pest haplotype, suggest that populations of R. similis in Australia were introduced from a single source population, most likely from the Southeast Asian region. This might not be the case in Africa, where extensive genetic diversity has been found.     

Aggressiveness and Damage Potential of Central American and Caribbean Populations of Radopholus spp. in Banana

Monoxenic cultures of burrowing nematode populations extracted from banana roots from Belize, Guatemala, Honduras, and Costa Rica were established on carrot discs. Cultures of Radopholus spp. were also obtained from Florida, Puerto Rico, Dominican Republic, and Ivory Coast. The aggressiveness (defined as reproductive fitness and root necrosis) of these populations was evaluated by inoculating banana plants (Musa AAA, cv. Grande Naine) with 200 nematodes/plant. Banana plants produced by tissue culture were grown in 0.4-liter styrofoam cups, containing a 1:1 mix of a coarse and a fine sand, at ca. 27 °C and 80% RH. Banana plants were acclimated and allowed to grow for 4 weeks prior to inoculation. Plant height, fresh shoot and root weights, root necrosis, and nematode population densities were determined 8 weeks after inoculation. Burrowing-nematode populations varied in aggressiveness, and their reproductive fitness was generally related to damage reported in the field. Plant height and fresh shoot and root weight did not reflect damage caused by nematodes under our experimental conditions. Necrosis of primary roots was closely related to the reproductive fitness of the nematode populations. Variation in aggressiveness among nematode populations followed a similar trend in the two susceptible hosts tested, Grande Naine and Pisang mas. All nematode populations had a low reproductive factor (Rf ≤2.5) in the resistant host except for the Ivory Coast population which had a moderate reproductive factor (Rf ≤ 5) on Pisang Jari Buaya. This is the first report of a burrowing nematode population parasitizing this important source of resistance to R. similis.     

Effects of Rhizophagus irregularis MUCL 41833 on the reproduction of Radopholus similis in banana plantlets grown under in vitro culture conditions

The role of arbuscular mycorrhizal fungi (AMF) in the control of migratory endoparasitic nematodes is nowadays largely admitted. Most studies were conducted under greenhouse conditions and a few used in vitro cultures with transgenic root organs. Here, we reported, for the first time, on the interaction between an AMF, Rhizophagus irregularis MUCL 41833 and Radopholus similis in roots of banana plantlets grown under in vitro culture conditions. The banana plantlets were pre-mycorrhized in an extraradical mycelium network arising from a Medicago truncatula donor seedling, before transfer to an autotrophic in vitro cultivation system and subsequent nematode inoculation. Both microorganisms were able to complete their life cycle in the absence as well as in presence of each other. The total R. similis population (i.e., summed over the roots and growth medium) as well as the surface of root necrosis was significantly reduced by 60 and 56 %, respectively, in the AMF-colonized banana plantlets. By contrast, nematodes had no visible impact on root colonization (i.e., percentage of arbuscules, intraradical spores/vesicles, and hyphae) by AMF and on the number of spores and hyphal length produced in the medium. These results clearly demonstrated that pre-mycorrhized banana plants could outcompete R. similis, while root colonization was not affected by the nematodes. They underline the interest of the novel in vitro cultivation system as a promising tool to investigate the biochemical factors and molecular mechanisms involved in the bio-protection conferred by AMF to a major root pathogen of banana.     

Dual inoculation of Fusarium oxysporum endophytes in banana: effect on plant colonization,growth and control of the root burrowing nematode and the banana weevil

The burrowing nematode (Radopholus similis (Cobb) Thorne) and the banana weevil (Cosmopolites sordidus Germar, Coleoptera: Curculionidae) are major pests of banana (Musa spp.) in the Lake Victoria basin region of Uganda. Among biological options to control the two pests is the use of non-pathogenic Fusarium oxysporum Schltdl.: Fries endophytes of banana. We investigated the ability of endophytic F. oxysporum isolates Emb2.4o and V5w2 to control the banana weevil and the burrowing nematode, alone and in combination. Plant colonization by the endophytes was determined by inoculating their chemical-resistant mutants separately and in combination, onto banana roots. Plant growth promotion was determined by measuring plant height, girth, number of live roots and fresh root weight at harvest, and control of the nematode and weevil was determined by challenging endophyte-inoculated plants with the pests 8 weeks after endophyte inoculation. Endophytic root colonization was highest in plants inoculated with both endophytes, compared with those inoculated with only one of the endophytes. Root colonization was better for isolate V5w2 than Emb2.4o. Dually inoculated plants showed a significant increase in height, girth, fresh root weight and number of functional roots following nematode challenge. Nematode numbers in roots were reduced 12 weeks after challenge of 8-week-old endophyte-inoculated plants. Significant reductions in weevil damage were observed in the rhizome periphery, inner and outer rhizomes, compared with endophyte non-inoculated controls. We conclude that dual inoculation of bananas with endophytic isolates Emb2.4o and V5w2 increases root colonization by the endophytes, reduces nematode numbers and weevil damage, and enhances plant growth in the presence of nematode infestation.     

Non-pathogenic Fusarium oxysporum endophytes provide field control of nematodes,improving yield of banana (Musa sp.)

Endophytic colonization by the fungus Fusarium oxysporum can result in increased host resistance to pests and diseases, and greater biomass production. However, few studies have assessed the field performance of this fungus for biological control of pests and diseases in banana. Further to greenhouse assessment, studies were carried out to evaluate the performance of F. oxysporum strains against plant-parasitic nematodes on banana (Musa sp., cv. Giant Cavendish and cv. Grand Nain) in the field using tissue-cultured plants. Plants were inoculated separately with one of three strains (V5W2, Eny 7.11o and Emb 2.4o) before being inoculated with Pratylenchus goodeyi and Helicotylenchus multicinctus in an on-station trial and in an on-farm trial planted in a field naturally infested with the same nematodes. All three endophytic strains significantly suppressed P. goodeyi and H. multicinctus densities and damage in the field. On-station, nematode population densities were reduced by >45% in endophyte-inoculated plants compared to non-inoculated plants, while percentage root necrosis was reduced by >20%. Similarly, on-farm, nematode damage to roots and densities were also significantly lower in endophyte-inoculated plants compared with control plants. Significantly improved yields were observed for plants inoculated with endophytes when compared to the control plants, with inoculation with strains Emb 2.4o and V5W2 resulting in up to 35% and 36% increased banana yields, respectively, for the on-station trial. For the on-farm trial, up to 20% increase in yields were observed for strain Eny 7.11o compared to control plants. This study provides the first report from the field in Africa on the reduction of nematode populations and damage, and the increase in banana production by fungal endophytes. The study shows that endophytes have potential to enhance yields of tissue-cultured banana plants and protect them against pests.     

Biological control of Radopholus similis in banana by combined application of the mutualistic endophyte Fusarium oxysporum strain 162, the egg pathogen Paecilomyces lilacinus strain 251 and the antagonistic bacteria Bacillus firmus

The biological control efficacy of single or multiple applications of the mutualistic endophyte Fusarium oxysporum strain 162, the egg pathogen Paecilomyces lilacinus strain 251 and the antagonistic bacteria Bacillus firmus toward Radopholus similis was investigated in pot trials with banana under glasshouse conditions. R. similis was controlled substantially in single and combined applications of F. oxysporum with P. lilacinus or B. firmus. The combination of F. oxysporum and P. lilacinus caused a 68.5% reduction in nematode density whereas the individual applications reduced the density by 27.8% and 54.8% over the controls, respectively. Combined application of F. oxysporum and B. firmus was the most effective treatment in controlling R. similis on banana (86.2%), followed by B. firmus alone (63.7%). The compatibility of the biocontrol agents, as well the capacity of F. oxysporum to colonize banana roots in the absence or presence of P. lilacinus was also investigated. P. lilacinus did not adversely affect endophytic colonization by F. oxysporum. Biological control of R. similis in banana can therefore be enhanced via combined applications of antagonists with different modes of action that target different stages in the infection process. Handling editor: Ralf-Udo Ehlers     

Comparative host tissue Réactions of Musa acuminate (AAA group) cvs Poyo and Gros Michel roots to three banana-parasitic nématodes

In a comparative histopathological investigation, Poyo and Gros Michel cul-tivars of Musa acuminata (AAA triploid) were inoculated with Radopholus similis, Helicotylenchus multicinctus or Hoplolaimus pararobustus and were grown in a greenhouse under tropical conditions. R. similis infected all the cortical parenchyma layers of the roots, reaching the vascular cylinder, but it stayed more superficial in Gros Michel roots. Red-brown cytoplasmic globules appeared in the cortical parenchyma cells of Gros Michel only. H. multicinctus infected much of the outer cortical parenchyma in roots of both cultivars with a few phenolic cells occurring around the superficial lesions. H. pararobustus penetrated only the immediate sub-epidermal tissues in both cultivars. The differences observed between nématodes and cultivars reflect specific host-nematode interactions on bananas.     

Relationships between nematodes, weevils, banana and plantain cultivars and damage

Infestation of banana and plantain suckers by nematodes (Pratylenchus good-eyi, Radopholus similis and Helicotylenchus multicinctus) and weevils (Cosmopolites sordidus) increased with time from establishment in a field of eight different cultivars. There was a strong association between nematode and weevil infestation; suckers infested with nematodes were more than four times more likely to be infected by weevil than suckers without nematodes. Weevil damage, measured by percentage coefficient of infestation (PCI) at harvest of the bunch, was higher on a plantain (cv. Gonja) and on an east African highland cooking banana (cv. Lusumba) than on the sweet and multi-purpose cultivars. There was a correlation between numbers of male weevils caught in a plot and the mean PCI measured in the plot, but no correlation with female numbers.     

Control of plant-parasitic nematodes by Paecilomyces lilacinus and Monacrosporium lysipagum in pot trials

The common soil inhabiting nematophagous fungus Paecilomyces lilacinus (Thom) Samson and the nematode trapping fungus Monacrosporium lysipagum (Drechsler) Subram were assayed for their ability to reduce the populations of three economically important plant-parasitic nematodes in pot trials. The fungi were tested individually and in combination against the root-knot nematode Meloidogyne javanica (Treub) Chitwood, cereal cyst nematode Heterodera avenae Wollenweber, or burrowing nematode Radopholus similis (Cobb) Thorne on tomato, barley and tissue cultured banana plants, respectively. In all cases, nematode populations were controlled substantially by both individual and combined applications of the fungi. Combined application of P. lilacinus and M. lysipagum reduced 62% of galls and 94% of M.␣javanica juveniles on tomato when compared to the experiment with no fungi added. Sixty five percent of H. avenae cysts were reduced on barley by combined application of fungi. Control of R. similis on banana, both in the roots and in the soil, was greatest when M. lysipagum was applied alone (86%) or in combination with P. lilacinus (96%), using a strategy where the fungi were inoculated twice in 18 weeks growth period. Overall, combined application of P. lilacinus and M. lysipagum was the most effective treatment in controlling nematode populations, although in some cases M. lysipagum alone was as effective as the combined application of fungi, particularly against M. javanica.     

Comparative study on the host susceptibility of different banana cultivars to plant parasitic nematodes in Malappuram district of Kerala,India

Six cultivars of banana grown widely in Malappuram district of Kerala were evaluated for the diversity of plant parasitic nematodes in their respective rhizosphere. The genotypes evaluated include Nendran, Poovan (Mysore), Njali poovan, Mysore poovan, Chenkadali and Ponnan. The study aims on a comparative analysis of rhizosphere of different banana varieties for the occurrence of plant parasitic nematodes, diversity, frequency of occurrence and to determine the most vulnerable type of banana variety. Cobb’s decanting and sieving method was used to isolate nematodes from soil. Thirty three samples randomly collected from different blocks of Malappuram district are subjected to analysis and a ten species of nematodes were reported. Among the six varieties analysed both Nendran and Mysore Poovan variety seems to be more susceptible to phytoparasitic nematodes. With respect to eight blocks of Malappuram district, Helicotylenchus sp. shows highest prominence value followed by Radopholus similis, reniform nematode and Meloidogyne incognita.