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

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

Infestation mechanisms of two woodborer species in the mangrove Sonneratia alba J. Smith in Kenya and co-occurring endophytic fungi

Insect damage on trees can severely affect the quality of timber, reduce the fecundity of the host and render it susceptible to fungal infestation and disease. Such pathology weakens or eventually kills the host. Infestation by two insect woodborer species (a moth and a beetle) is causing mortality of Sonneratia alba, a wide-ranging pioneer mangrove species of the Indo-Pacific. Establishing the infestation mechanism of the two insect woodborer species is an initial and essential step towards understanding their ecological role in the mangroves and in determining sustainable management priorities and options. Our main objectives were to investigate the infestation mechanism employed by the two insect woodborers which infest S. alba trees, to establish the occurrence of secondary infestation by endophytic fungi in the infested S. alba branches, and to explore a control management option to the woodborer infestation. We conducted an external inspection of infested branches in two large embayments in Kenya, Gazi Bay and Mida Creek, and by splitting infested branches we determined the respective internal infestation mechanisms. Infested wood samples from Gazi Bay and Mida Creek were incubated at 28±1°C for 3-5 days to establish the presence of fungi. A survey was conducted in both Gazi Bay and Mida Creek to ascertain the presence of ants on S. alba. The infestation characteristics of the two insect woodborer species were different. It took 6-8 months for the beetle to kill a branch of 150 cm-200 cm long. For the moth to kill a branch, it depended upon several factors including the contribution by multiple species, other than the moth infestation alone. A total of 15 endophytic fungal species were identified. Two ant species Oecophylla longipoda and a Pheidole sp. inhabited 62% and 69% respectively of sampled S. alba trees in Gazi Bay whereas only Pheidole sp. inhabited 17% of the sampled S. alba trees in Mida Creek. In summary, we have documented the time it takes each woodborer species to kill a branch, the infestation mechanism of the two insect woodborers, and we hypothesized on the role of two ant species. The presence of several different fungal species was ascertained, and we discussed their possible role in the infested wood. Our results cannot unambiguously associate the woodborers and identified fungi. We recommend further studies to investigate the presence or absence, and if present, the nature of fungi in the gut of the woodborers

Soil fertility management in sub-Saharan Africa

Published online: 04 May 2017Most of the population in sub-Saharan Africa depends on agriculture for livelihood, which is mainly practiced by resource-constrained smallholder farmers. Due to persistent low crop yields, food and nutrition insecurity, farmers have been opening new lands through deforestation or encroachment into marginal lands where possible, seeking for additional yields, which has aggravated soil erosion, land degradation, and eutrophication of water bodies. Adoption of integrated soil fertility management practices in the smallholder farming systems has been affected by several factors including poor access to improved agricultural inputs, poor understanding of the practices and their benefits, and importantly limited financial capacity. Here we review challenges of soil fertility management in the smallholder farming systems of sub-Saharan Africa. Our major findings are: (1) most countries have not been able to meet the fertilizer target of 50 kg nutrients ha−1 by 2015 in the 2006 Abuja Declaration; over 65% of the smallholder farmers have not used fertilizer and 75% of the agricultural soils have been affected by nutrient depletion. (2) Poor agricultural practices have resulted in an average annual nutrient loss of 50 kg ha−1, which represented an equivalent of US$ four billion lost in 2008 and an estimated economic cost of up to 18% of the gross domestic product in addition to eutrophication of water bodies. (3) Value cost ratios of agricultural inputs that are less than three are common, which has limited the profitability of integrated soil fertility management practices. (4) Proliferation of fake agricultural inputs has been reported in over 40–60% of the cases as a consequence of poor enforcement of quality standards. (5) In addition to blanket recommendations, fertilization has focused on nitrogen, phosphorus and potassium, with little emphasis on secondary and micro-nutrients as well as organic amendments or liming materials in acid soils, which has generally resulted in poor crop responses or low yield increments. (6) Effective adoption of integrated soil fertility management would result in at least doubling the current nutrient agronomic use efficiency in the smallholder farming systems and reduction of the actual yield gap averaged to more than 300% for cereal and legume crops. Based on these findings, operationalization of supportive policies to increase adoption of good agronomic practices and investment in research to develop solutions appropriate to smallholder farmers should be recommended