Browsing by Subject "Banane"

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Banana weevil borer (Cosmopolites sordidus)
plant defense responses and control options
(2021) Bakaze, Elyeza; Wünsche, Jens Norbert
Each year 25-75% of banana yields are lost to Cosmopolites sordidus, one of the major pests of banana/plantain plants. This loss is common with resource-limited farmers who cannot afford the frequent application of insecticides due to their cost and developed resistance by weevils. Larvae, the most destructive life stage, occupy ecologically different microenvironments from adult weevils, thus least affected by synthetic insecticides. Feeding of larvae on banana rhizomes interferes with the established and emerging roots which reduce water and nutrient uptake and consequently weaken the plant stability during windy weather. Integrated pest management (IPM) is being promoted, for a single control strategy produces limited and or unsustainable results. IPM options for banana weevils include habitat management (cultural control), biological control, host resistance, botanical control and chemical control as last resort. Of the above IPM strategies, this research evaluated host resistance, botanical plant extracts and entomogenous fungi to contribute to the overall goal of reducing synthetic insecticides use. In the evaluation of host resistance, physiochemical of phenolic origin; lignin, and suberin were considered. Comparably, weevil and methyl jasmonate treatment, induced higher deposits of lignin and suberin, cellular modifications, and high total phenolic content as well as antioxidant capacity in “Km5” than “Mbwazirume” banana cultivars. Induced polyphenols reduced weevil damage to less than 5% in “Km5” compared to 11% damage in the “Mbwazirume” cultivar. However, with the onetime application of 0.01% methyl jasmonate, “Mbwazirume”, had 50% reduced weevil damage compared to untreated control. Extracts from dried clove buds (Syzygium aromaticum), pepper fruits (Piper guineense) and neem seeds (Azadirachta indica) and their synthetic analogs were evaluated as botanical control option to Carbofuran against C. sordidus in the laboratory and infested field experiments. Efficacy of plant extracts and their synthetic analogs, revealed egg hatch inhibitory effect, larvicidal toxicity and adult repellency variation. For instance, clove extracts and its synthetic analogs had the lower egg inhibitory dose (ID50) of 0.08 to 0.22% than black pepper (0.24 to 0.75%), and half the ID50 value caused 50% larvae mortality. However, in 6 to 48 hours pepper repelled 80 - 98%, clove 78 - 90% and neem 63 - 75% adult weevils, an effect that significantly (P =0.001) reduced field weevil population. Lastly, three Entomogenous fungi; Curvularia senegalensis, Fusarium verticillioides, and Fusarium oxysporum species complex (FOSC) were also evaluated for their ability to infect weevil eggs, larvae and adult weevils, and to reduce weevil damage in potted plants. C. senegalensis and F. verticillioides greatly affected egg hatching and larval survival, for instance, they caused 75 to 90% eggs hatch inhibition, unlike the 25 to 55% egg hatch inhibition for Beauveria bassiana and FOSC. Besides that, fungal treated plants 14 days before weevils, had significantly high SPAD value (P <0.0001), less than 20% rhizome damage and predictive weevil mortality R2 = 0.46. Rhizome damage was greatly reduced by C. senegalensis, followed by B. bassiana and F. verticillioides, and it is the first record to demonstrate that C. senegalensis and F. verticillioides are pathogenic to C. sordidus. In conclusion, an IPM that combines host resistance with locally available botanic extracts and effective entomogenous fungi may provide a sustainable intervention in the management of the weevil population and their damages to benefit both commercial and resource-limited farmers.
Innovative propagation techniques in banana and plantain
(2020) Opata, John; Wünsche, Jens Norbert
Despite the significant role of banana and plantain (Musa spp.) in the livelihood of millions of people mostly in developing countries and in particular Sub-Saharan Africa, cultivation of these important crops is impeded by numerous challenges. Against this backdrop, research attempts were made to improve shoot proliferation in banana and plantain by employing innovative macropropagation techniques. Banana and plantain suckers were harvested in the greenhouses of the University of Hohenheim, Stuttgart, Germany and research fields of the Crops Research Institute, Ghana. These were subjected to Plants Issus de Fragments de tige technique (PIF), which is a mechanical preparation technique. It involves paring, thus cutting off the roots of the corms with a sharp sterilized knife. Thereafter, the leaf sheaths of the corms were carefully removed, consequently exposing latent axillary buds and the apical shoot meristem. Some of the corms had the exposed meristem destroyed with crosswise incision whiles others had the meristem left intact. Various hormonal treatments with the synthetic plant hormone 6-benzylaminopurine (0, 2.25 and 225.25 mg L-1 BAP) and natural plant hormones derived from coconut water were used. Fresh and autoclaved coconut water and other additives such as papain and root growth biostimulant from seaweed were employed in various combination to treat banana and plantain corms by either soaking or vacuum infiltration. The treated corms were planted in germination beds filled with growth substrates inside growth chambers. Evaluation of solution uptake from the two application methods and subsequently effects on number and growth characteristics of lateral shoots from the treated corms were carried out. Field evaluation of growth and yield of acclimatized plantlets from the PIF technique and hormonally derived plantlets were also undertaken. The hormonal solution application method demonstrated a higher solution uptake with the method of infiltration which was about 33% more compared to the method of soaking. Results revealed an earlier shoot emergence in corms which had the apical meristem destroyed with crosswise incision, demonstrating the breakdown of apical dominance. Nonetheless, this did not contribute to significantly higher shoot numbers when compared to corms with intact apical meristem. BAP treated corms had triggered greater number of strong shoots with comparatively higher number of roots than untreated controls, however, the effect was independent of the concentration applied. The study further revealed the importance of natural growth hormones particularly the application of autoclaved coconut water as an alternative to the expensive plant growth hormone, 6-benzylaminopurine. There was a marked effect of autoclaved coconut water, resulting in earlier shoot development characterized with higher root numbers compared to corms subjected to 6-benzylaminopurine and the PIF technique, respectively. Moreover, the addition of the proteolytic enzyme papain and the root growth biostimulant seaweed extract to coconut water did not influence the growth performance of the treated corms. Vegetative growth performance, specifically pseudostem length of the main crop, was significantly influenced by the treatment at 6 and 9 months of growth in the field. BAP and seaweed extract recorded the highest numbers of suckers. Uniformity of acclimatized plantlets with well-developed roots and active leaves at the nursery stage might have contributed immensely for the uniform vegetative growth. Treating the corms with BAP and seaweed significantly influenced the bunch weight of the main crop resulting in a bunch weight of about 11 kg. However, there was no significant difference among treatments regarding bunch weight of the first sucker crop with each treatment recording a bunch weight of 11 kg.
Mechanistic aspects of the eco-physiology of Fusarium oxysporum f. sp. cubense TR4
(2023) Were, Evans; Rasche, Frank
Banana and plantain (Musa spp.), here termed as bananas, are a source of food security and income for more than 400 million people globally. Banana production is threatened by Fusarium wilt disease, caused by the soilborne root-infecting fungal pathogen Fusarium oxysporum f. sp. cubense (Foc). Foc Tropical Race 4 (Foc TR4) is considered the most virulent race of Foc and has gained notoriety due to its inexorable spread and devastating impact on banana cultivation. Host infection occurs when pathogen propagules, called chlamydospores, germinate and produce hyphae that penetrate host roots and subsequently invade host tissues. Infection occurs in a narrow zone of soil immediately adjacent to the roots, called rhizosphere. The rhizosphere is notable for the extensive interactions between roots, the microbiome, and soil physico-chemical factors. Banana rhizosphere interactions are poorly understood, yet profoundly influence infection and development of Fusarium wilt. It is speculated that a better understanding of banana rhizosphere interactions will improve management of Fusarium wilt through the reduction of the abundance and/or efficacy of inoculum or enhance the disease suppressiveness of soils. Hence, the overarching objective of this doctoral study was to contribute to the fundamental ecological understanding of banana rhizosphere interactions related to Foc. The first study of this thesis analysed literature from four electronic databases (AGRIS, CAB Direct, SciVerse Scopus, ProQuest) to bring together the relatively scant data available on banana rhizosphere interactions and to highlight the key knowledge gaps. Analysis of 2,281 publications revealed the complexity of banana rhizosphere interactions and the driving factors of Fusarium wilt, for which the mechanisms remain poorly understood. Data from the literature shows that management of Fusarium wilt through rhizosphere manipulation is a dominant element albeit with limited success in the field. Notably, the data from literature shows that biological control agents (bacterial and fungal strains) are highly effective in vitro and in the greenhouse with a mean efficacy of 77.1% and 73.5%, respectively, but efficacy remains below 25.0% under field conditions. The second study of this thesis provides empirical evidence for suppression of Foc TR4 by root-secreted phenolic acids of non-host plants. Hydroponic culture and targeted metabolite analysis of root exudates of two legumes, Desmodium uncinatum and Mucuna pruriens, identified phenolic compounds such as benzoic-, t-cinnamic-, and p-hydroxybenzoic acid with inhibitory potential. These phenolic compounds suppressed Foc TR4 by inhibition of chlamydospore germination, production of new spores, and hyphal growth, and specifically also the biosynthesis of fusaric acid and beauvericin toxins, which are essential in the biology of the fungus. The third study of this thesis provides empirical evidence that the process of chlamydospore germination in Foc TR4 is developmentally orchestrated and iron-dependent. Scanning electron microscopy showed that iron-starved chlamydospores are unable to form a germ tube and exhibit reduced metabolic activity. Moreover, germination exhibits plasticity regarding extracellular pH, where over 50% germination occurs between pH 3 and pH 11. This suggests that disease suppression by manipulation of soil pH may not necessarily act via alteration of iron bioavailability. The requirement for iron was further investigated by assessing the expression of two genes (rnr1 and rnr2) that encode ribonucleotide reductase (RNR), the enzyme that controls cell growth through DNA synthesis. Expression of rnr2 was significantly induced in iron-starved chlamydospores compared to the control. The fourth study assessed the production of microbial iron-sequestering metabolites (siderophores) as a potential mechanism to counteract iron starvation. Specifically, ferrichrome, a hydroxamate siderophore, was synthesized exclusively in the mycelia of iron-starved cultures, which suggests de novo biosynthesis. Moreover, amino acid precursors for siderophore biosynthesis (ornithine, arginine) were altered by iron starvation. Collectively, this doctoral thesis extends the fundamental understanding of the biology and ecology of Foc TR4 and provides a base for realizing the potential of rhizosphere manipulation for management of Fusarium wilt.