Arbuscular mycorrhizal fungi in the East African Highland banana cropping systems as related to edapho-climatic conditions and management practices: case study of Rwanda

Root colonization, soil population density and diversity of arbuscular mycorrhizal (AM) fungi were assessed in 188 banana fields in contrasting soil types across five eco-regions in Rwanda (Butare-Gitarama, Gashonga, Bugarama, Kibungo, Ruhengeri). Root colonization was observed in all banana plants, whatever the soil type, field site and farm. The population density was higher on the wetter (1 300-1 500 mm yr(-1)) volcanic soils (Gashonga 59.8 and Ruhengeri 48.5 propagules 100 g(-1) soil, respectively) as compared to the dryer (900-1200 mm yr(-1)) soils derived from schist and granite (Butare-Gitarama 2.0, Kibungo 8.5, Bugarama 14.7 propagules 100 g(-1) soil). The diversity was highest in Kibungo and lowest in Butare-Gitarama (10 and 2 spore morphotypes, respectively). These results suggested that AM fungi were widespread in banana cropping systems in Rwanda, but that root colonization, population density and diversity varied considerably depending on edapho-climatic conditions (i.e. rainfall, soil texture and P content) and soil management practices (tillage). (C) 2009 Elsevier Ltd and The British Mycological Society. All rights reserved

Benefits and potential use of Arbuscular mycorrhizal fungi in banana and plantain systems in Africa

Crop plant association with arbuscular mycorrhizal fungi (AMF) often prove beneficial to crop productivity through a number of mechanisms, such as improved access to nutrients and water, pest and disease suppression. Banana and plantain are both mycorrhizal plants, with a number of studies demonstrating the strong stimulatory affect of AMF on plant growth in pots. Application of AMF to newly deflasked tissue culture plants or in nurseries therefore, may improve plant growth and possibly provide healthier plants for sale to farmers. Studies have also shown that plants are also better able to suppress nematodes in pots. However, how this association benefits banana and plantain growth, and consequently yield, under field conditions has yet to be properly determined. Studies are currently underway to determine the mycorrhizal associations of banana and plantain cultivars with AMF in East and Central Africa. Greenhouse studies complement field studies for comparison at the different levels. In West Africa, studies have been conducted to assess the AMF associations and yield impact following inoculation. Data is is accumulating, and showing variable composition and abundance of AMF species, with up to a total of 20 AMF species associated with banana plantations in East Africa. Spore abundance, inoculum reservoir that determines colonization, was largely influenced by management practices. However, the data generated to date, is increasingly indicating the importance of the management of banana systems, clearly indicating that banana and plantain are highly dependent on AMF. Some species also appear to be more superior in their effects on banana growth, nutrient uptake and the control of root damage by nematodes. Studies are in progress to screen AMF species and establish trials along different integrated soil fertility management practices. This paper reports on the available data surrounding the potential impact of AMF on banana and plantain in Africa

Preliminary investigations reveal that Bacillus thuringiensis δ-endotoxin CryIA(c) incorporated in soil does not affect arbuscular mycorrhiza in Sorghum bicolor (L.) (Moench)

The imminent introduction of transgenic crops into Kenya requires a rigorous assessment of the potential risks involved. This study focused on the possible effect of Bacillus thuringiensisδ-endotoxin [CryIA(c)] on arbuscular mycorrhizal fungi (AMF) associated with sorghum. In green house experiments, sorghum seedlings were inoculated with a mixed culture of AM fungi and grown in black cotton soil that contained increasing concentrations of B. thuringiensis toxin. The plants were sampled after 2, 4, 6 and 12 - week intervals. There was a progressive increase in AMF colonization from the 1st harvest (after 2 weeks) to the 4th harvest (after 12 weeks) in all treatments. Additionally, the total root length, fresh shoot weight and fresh root weight was not influenced significantly by the presence of the Bt toxin. These findings suggest that the presence of the Bt toxin in soil does not affect AM of sorghum. Keywords: Arbuscular mycorrhiza; fungi, Bacillus thuringiensis, endotoxins; CryIA(c), Sorghum bicolor; symbiosis Journal of Tropical Microbiology and Biotechnology Vol. 3(1) 2007: pp. 12-1

Application of rhizobacteria inoculants in biocontrol of Bacterial wilt (Ralstonia solanacearum) in potato (Solaum tuberosum) production.

Bacterial wilt is an important soil borne disease that threatens potato production. It is difficult to control due to the large number of hosts, high genetic and phenotypic variability of the pathogen, systemic localization of the pathogen, and lack of chemical control. Use of antagonistic microorganisms is critical due to their role in suppressing pathogenic infection. The objective of this study was to evaluate the effectiveness of three rhizobacteria isolates in suppressing of bacterial wilt on potato (cv. Tigoni and clone 387164.4). Potatoes were planted under controlled condition in complete randomized block design with 11 treatments: Azoctobacter, Bacillus and Pseudomonas as single, double and triplicate combinations, three organic amendments of poultry, cattle and compost manure and untreated control. Except for single Azoctobacter treatment all the microbial treatments and poultry manure suppressed bacterial wilt infection, reducing area under the disease progress curve by 13-40 compared to control with 53. Triple inoculation of Pseudomonas+Bacillus+Azoctobacter and duo inoculants of Bacillus+ Azoctobacter and Pseudomonas+ Azoctobacter had significantly (P<0.05) higher tuber weight of 362-418g compared to control with 143g. Apparently healthy tubers from Pseudomonas+Bacillus+Azoctobacter in clone 387164.4 were free from latent infection. There was however, no effect of the microbial inoculants and organic amendments on small and medium tuber grades and on tuber phosphorus content. These microbial inoculants were effective as biocontrols under controlled condition but more studies need to be undertaken to ascertain their effectiveness

Evaluation of commercial arbuscular mycorrhizal inoculants

In order to improve the use of commercial inoculants, 12 arbuscular mycorrhizal fungi (AMF) inoculants were evaluated in a two-step experiment under greenhouse conditions using maize. First, commercial mycorrhizal inoculants were propagated in a trap pot culture experiment under sterilized sand to evaluate their potential for maize (Zea may L.) root colonization as compared with an indigenous soil inoculum and to survey the AMF species present in the products. Three inoculants significantly increased root colonization levels compared with a soil inoculum. Instead of 12 declared AMF species, 13 fungal strains were extracted from the pot culture survey, including five undeclared species, while four declared species did not produce spores. In a second experiment, commercial products were inoculated into soil to assess their impact on maize growth and yield. Six weeks after planting, seven inoculants increased root colonization levels compared with control soil, while only three inoculants increased slightly the shoot biomass of maize plants. These experiments highlight the need to pre-evaluate commercial mycorrhizal inoculants on a selected crop and regional soil before launching large-scale field use.Afin d'optimiser l'usage des mycorhizes en agriculture, douze inoculants commerciaux de champignon mycorhizien arbusculaire (CMA) furent évalués en serres sur le maïs. Dans un premier temps, les inoculants furent propagés en pots sur sable stérilisé afin d’évaluer leur potentiel sur la colonisation racinaire du maïs par rapport à celui d'un sol agricole du Kenya et d'inventorier les espèces CMA contenues dans les inoculants. Trois inoculants augmentèrent le taux de colonisation racinaire comparé au sol agricole. Treize espèces AMF furent isolées des inoculants dont 5 non déclarées. Quatre des 12 espèces annoncées n'ont pas sporulé. Dans une seconde expérience, les inoculants furent utilisés en combinaison avec le sol agricole afin d’évaluer leur impact sur le rendement du maïs. Six semaines après le semis, 7 inoculants augmentèrent le taux de colonisation racinaire par rapport au sol témoin alors que 3 inoculants entraînèrent une légère augmentation de la biomasse aérienne. Ces évaluations démontrent la nécessité d'effectuer une pré-évaluation des inoculants commerciaux sur une culture et un sol donnés avant de les implanter à grande échelle

Indigenous Arbuscular mycorrhizal fungi and growth of tissue-cultured banana plantlets under nursery and field conditions in Rwanda

Arbuscular mycorrhizal fungi (AMF) have been , .. ridel), evaluated for their suitability in the acclimatization and nursery management of tissue-cultured (TC) plantlets of banana and plantain Improved growth and vigour of plantlets has been documented with exotic AMP species. A wide range of AMF species are associated with banana and plantain (Musa spp.) systems. In this studj~ the use of indigenous AMF from banana and plantain systems was evaluated for nursery management of TC plantlets. ASingle species inoculum with Glomus nwsseae was compared with two mixed inoculants, all derived from banana and plantain systems; these were evaluated on the cultivars 'Mpologoma' (AAA-EA) and 'Kamaramasenge' (AAB) established in two soil types, one with a low P concentration (16-22 mg/kg) and another with high P (50-80 mg/kg). Inoculation with A1-lF enhanced height and leaf surface area growth of Ie plantlets in both soils and both cu1tivars. The inoculation was more effective on 'Mpologoma' than on '](amaramasenge', and mixed inoculants were more effective than the Single-species inoculum, particularly under field conditions, where up to 30'% increase in height, girth and leaf surface area was recorded in 'Mpologoma'. The mixed AMF inoculant comprising species from the soil with low P availability (AMF Kibungo) was most effective in soils with a P concentration of 50-80 mg/kg. High yield was evident in inoculated plants, with a slightly over 30% yield increase for 'Mpologoma' and 'Kamaramasenge' at both the Rubona and Kibungo sites