Abstract:

The shea tree (Vitellaria paradoxa C. Gaertn.) is an indigenous tree species that is widely
distributed in the Sudano-Sahelian belt of Africa. In Uganda, it grows naturally in the
savannah parklands of northern and eastern parts of the country. It is widely known for its oil
which is produced from its kernels and used in cooking, cosmetics, traditional medicine and
cultural ceremonies. Due to its socioeconomic and cultural importance, a folk classification
has evolved among the local communities in the shea tree parklands of Uganda. Folk
classifications have been extremely useful in many crop improvement programmes. In
Uganda, folk classification recognises the presence of shea tree ethno-varieties on the basis of
fruit and nut differences. However, these ethno-varieties are faced with extinction due to
extraction pressures (for the provision of charcoal, poles and firewood) and neglect due to
lack of a shea tree improvement programme. This study was conducted in three farming
systems (northern, Teso and West Nile) of the shea tree belt of Uganda to document the folk
classification and characterise local ethno-varieties as a basis for conservation and future
improvement/breeding programmes. The objectives were 1) to document folk classification
and management of shea tree ethno-varieties in Uganda based on farmers’ criteria; 2)
examine the morphological variation within and among the different shea tree ethno
varieties; 3) analyse the fat content and fatty acid composition within and among these ethno
varieties; and 4) assess the genetic diversity and molecular variation within and among the
different shea tree ethno-varieties. Folk classification was investigated using participatory
rural appraisal (PRA) tools, morphological variation was assessed using morphometric
measurements while chemical analysis was conducted by Near Infrared Spectroscopy (NIRS)
and conventional wet chemistry (soxtec petroleum – ether and gas chromatography). Nuclear
simple sequence repeats (SSRs) were used to determine the molecular variation among the
ethno-varieties. The results show 36 different uses of shea trees and their products, 24 of
them based on shea oil, making it the most frequently used product. The local communities
manage shea trees through practices such as weeding, pruning and on-farm retention.
Traditional conservation practices are influenced by belief systems involving taboos and
rituals. A total of 44 ethno-varieties based on single fruit and nut morphological and
organoleptic traits were documented across the three farming systems in the shea parklands
of Uganda. Quantitative morphometric data showed no clear aggregation that is congruent to
folk classification indicating that the ethno-varieties cannot be adequately distinguished on
the basis of morphological traits. Morphological traits such as pulp weight, stem diameter,fruit weight and canopy diameter were highly variable between individual trees suggesting
that the environment may influence morphology to a large extent. With regard to fat content,
and fatty acid composition, all ethno-varieties were dominated by oleic and stearic acids.
Other fatty acids include palmitic, vaccenic, linoleic, linolenic and arachidic acids. Pairwise
comparisons did not find any significant variation in fatty acid composition between ethno
varieties. Shea tree ethno-varieties can therefore not be distinguished on the basis of fat
content and fatty acid composition. In terms of molecular variation, most variation (86.90%)
occurred within individual trees while 8.43% was found among individual trees within ethno
variety groupings and 4.67% was found among ethno-variety groupings. All shea tree ethno
variety groupings constitute a single out-crossing population with very low genetic
differentiation and high gene flow. In conclusion, this study shows that the ethno-varieties as
perceived by farmers in the shea parklands of Uganda are arbitrarily defined sub-groups of a
single randomly mating population.