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Other publication, 2012

Allanblackia – a tree crop under current domestication: What are the soil requirements and symbionts?

Ström, Helena; Alvum-Toll, Kajsa; Dahlin, Sigrun; Fransson, Petra; Ofori, Daniel; Jamnadass, Ramni


In order to improve livelihoods and enhance food security and resilience of rural communities, diverse and multifunctionalagricultural systems are promoted. There has long been a lack of investment in domestication of plant species that arespecifically suited to African farmers' circumstances, but there is now a growing demand for commercialization and use of localcrops and trees. One example is the indigenous tree Allanblackia which seeds contain high-value edible oil. Traditionally,Allanblackia seeds have been collected from wild stands by rural communities, but more recently access to wild stands isthreatened by deforestation. During the last decade, Allanblackia oil has further received attention from industry as raw materialin the production of spreads and soaps, increasing the demand for Allanblackia seeds. In response to this ICRAF in 2002launched a research program aiming for the domestication of Allanblackia tree species on smallholder farms. Up to now,research activities have focused on selection of highly productive plant materials and propagation methods. However, to fullyoptimize the harvest potential of domesticated Allanblackia, the trees´ requirements for nutrients and water must be met, butknowledge on this is largely lacking. Work carried out on management of Allanblackia seedlings at the nursery has preliminarilyshown that incorporation of soil collected from native Allanblackia stands in the potting medium enhances growth of seedlings,indicating a positive plant-microbial interaction. Symbiotic relationships between plants and micro-organisms are very commonand often stimulate nutrient and water uptake from the soil. However, in this case it remains to clarify if such interaction existsand, if so, which organisms are involved and how they can be promoted in the nursery and on farm-land. The purpose of thisstudy is to obtain information about the environmental requirements of Allanblackia and it has two main objectives. The generalsoil chemical and physical parameters of natural A. stuhlmannii stands will be determined and will with information on climaticconditions and the soil water regime be used to characterise the abiotic requirements of the species. Biological enhancing factorswill be sought, with a particular focus on mycorrhizal symbionts. The fieldwork will be carried out during August-September2012, in the Eastern Arc Mountains, Tanzania. Together with local expertise and researchers at ICRAF, native Allanblackiastands will be localised and site characteristics, such as elevation, slope and drainage assessed. In addition, soil samples will becollected for characterisation of chemical and physical properties, such as soil pH, major plant nutrients, soil organic carbon, soiltexture, bulk density and water holding capacity. The root systems will also be traced from the tree and root fragments collected,bleached and stained. These will subsequently be examined for occurrence of arbuscules and vesicles in the search for possiblesymbionts, and degree of colonisation determined. The study will provide knowledge on the environmental requirements andbiological relationships essential for understanding the tree's biology and appropriate cultivation practices and thus contribute tothe domestication process. Preliminary results will be presented at the conference.

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Title: Integrated Soil Fertility Management in Africa: from Microbes to Markets (ISFM Africa 2012)