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Publications

NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.

2023

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Abstract

Apple stem grooving virus (ASGV) is one of the most widespread and asymptomatic main viruses, that restricts the production of apples worldwide. Establishment of rapid, simple, and effective early detection methods of apple virus is important. In this study, we established and optimized a one-step reverse transcription - recombinase polymerase amplification (RT-RPA) method, using the target-specific primers of ASGV coat protein gene sequence, and M-MLV reverse transcriptase. This method could be completed within 30 min at 40 °C, followed by a visual detection of the results within 5 min by using lateral flow dipstick (LFD). The specificity results showed that only samples infected with ASGV showed a test line, while no test line appeared in the ASGV-negative samples. In addition, when crude extract of leaves was used, the whole detection could be completed within 1 h, which was shortened by 4 to 6 times compared with the RT-PCR method. The detection made on more field samples showed that the RT-RPA-LFD method is of high stability and reliability for ASGV diagnosis, with a great potential in the rapid on-site detection of plant viruses.

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Abstract

Coffee is an important commodity for Kenya, where production is steadily declining, despite a global rise in demand. Of the various constraints affecting production, plant-parasitic nematodes are a significant, but often overlooked, threat. As a perennial crop, treating plantations once infected with nematodes becomes difficult. The current study evaluated the drenching application of two biocontrol agents, Trichoderma asperellum and Purpureocillium lilacinum, for their nematode control efficacy, as well as their impact on the soil nematode community structure on mature, established coffee trees in Kenya. Seven Arabica coffee field trials were conducted over two years on trees of various ages. All the fields were heavily infested with Meloidogyne hapla, the first report of the species on coffee in Kenya. Both fungal biocontrol agents were detected endophytically infecting roots and recovered from soil but not until six months after initial applications. The population densities of M. hapla had significantly declined in roots of treated trees 12 months after the initial application, although soil nematode density data were similar across treatments. Based upon the maturity index and the Shannon index, treatment with T. asperellum led to improved soil health conditions and enrichment of diversity in the microbial community. Application of P. lilacinum, in particular, led to an increased abundance of fungivorous nematodes, especially Aphelenchus spp., for which P. lilacinum would appear to be a preferred food source. The soils in the trials were all stressed and denuded, however, which likely delayed the impact of such treatments or detection of any differences between treatments using indices, such as the functional metabolic footprint, over the period of study. A longer period of study would therefore likely provide a better indication of treatment benefits. The current study positively demonstrates, however, the potential for using biologically based options for the environmentally and climate-smart management of nematode threats in a sustainable manner on established, mature coffee plantations.

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Abstract

Potato Cyst Nematodes (PCN) (Globodera rostochiensis and G. pallida Woll.) are quarantine pests of potato (Solanum tuberosum L.) worldwide capable of causing significant yield loss and difficult to manage with conventional methods. The study explored the diversity of antagonistic fungi associated with PCN obtained from soil samples collected in Nyandarua and Nakuru Counties in Kenya and their effect on PCN egg viability and hatching was also evaluated. Twelve fungal isolates from five genera were isolated and characterized using morphological and molecular techniques. The twelve isolates were Trichoderma asperellum (4), T. hamatum, T. breve, T. atrobruneum, Amanita basiorubra, Setophoma terrestris (2), Penicillium chrysogenum and Clonostachys rosea. The most abundant isolate was Trichoderma spp. with 58 % occurrence. The effect of seven of the isolates on PCN eggs showed that T. breve and P. chrysogenum reduced egg viability by 41 % and 34 %, respectively while T. asperellum and T. breve reduced their hatching by 50 % on average. Trichoderma atrobrunneum, T. hamatum, and A. basiorubra also reduced the PCN egg viability by 27 % on average. These fungal isolates could provide a potential tool for PCN management in potato production systems for improved yields. However, further studies are warranted to validate these findings under greenhouse and field conditions. A more comprehensive bioprospecting survey for PCN associated antagonistic fungi needs to be extended to other potato growing regions to explore further cyst pathogens.

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Abstract

The root-burrowing nematode, Radopholus similis, is reputedly the most damaging nematode pest of banana and responsible for major production losses. In this study, the endophytic potential of 13 fungal isolates was assessed for the management of R. similis in East African Highland bananas (‘Ng’ombe’). All isolates successfully colonised tissue-cultured banana roots, with isolates from Trichoderma, Fusarium and Hypocrea producing the highest (⩾49.1%) and Beauveria isolates the lowest (⩽14.4%) colonisation. The fungal endophytes T. asperellum (ICIPE 700) and H. lixii (ICIPE 697) were the most effective in reducing R. similis densities (>81%) relative to the non-inoculated control. However, the combined inoculation of ICIPE 700 and ICIPE 697 led to greater suppression of R. similis (>21%) relative to individual inoculation. Suppression of R. similis following inoculation of banana roots with ICIPE 700 and/or ICIPE 697 was associated with the significant upregulation of the defence-related gene PR-1, the cell signalling gene calmodulin Ca2+ and the cell-wall-strengthening gene β-1,3-glucan synthase. This study demonstrates the potential for nematode management in bananas with fungal endophytes, especially using the isolates ICIPE 700 and ICIPE 697 when combined.

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Abstract

The legume cavalcade, Centrosema pascuorum, is used extensively as a cover crop and as a component of conservation agriculture systems. It is also an attractive rotation or cover crop for the management of root-knot nematodes (RKN; Meloidogyne spp.) as it is a non-host. RKN are persistent pests that are well known to be difficult to control. However, the mechanisms governing the non-host status of cavalcade is unknown. The current study established that cavalcade leaves are toxic to RKN as either aqueous extracts or soil amendments. Bioassays conducted using Meloidogyne javanica showed that a 90% concentration of aqueous extract derived from 1-month-old cavalcade leaves (89 mg crude extract ml−1) suppressed nematode hatch (82.9%) and killed infective second-stage juveniles of M. javanica (85.3%). Soil amendments with 1% (w/w) of 1-month-old cavalcade leaves (0.99 mg crude extract g−1 soil) also provided effective control of M. javanica in the glasshouse on okra. One-month-old leaves appeared more effective than 2- or 3-month-old leaves. The soil amendments had no adverse phytotoxic effect on okra seed germination. Our study demonstrates the potential for using cavalcade leaves or extracts to manage RKN. This may be due to the nematicidal activity of the various compounds in the leaves, such as flavonoids, phenols and terpenoids, which should be further assessed.

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Abstract

The gut microbiota plays an important role in host health and disease. Our understanding of the fish microbiota lags far behind our knowledge of that of humans and other mammals. Nevertheless, research has highlighted the importance of the microbiota in the health, performance, and various physiological functions of fish. The microbiota has been studied in various fish species, including model animals, economic fish, and wild fish species. The composition of the fish microbiota depends on host selection, diet, and environmental factors. The intestinal microbiota affects the nutritional metabolism, immunity, and disease resistance of the fish host, while the host regulates the intestinal microbiota in a reciprocal way through both immune and non-immune factors. Improved and novel gnotobiotic fish models have been developed, which are important for the mechanistic study of host-microbiota interactions in fish. In this review, we discuss recent progress in fish microbiota research. We describe various aspects of this research, including both studies on fish microbiota variations and fundamental research extending our knowledge of host–microbiota interaction in fish. Perspectives on how fish microbiota research may benefit fish health and industrial sustainability are also discussed.