Abstract:
: Shea is an agroforestry tree species known primarily for its rich butter, which contains
stearin and tocopherol, and has ultraviolet ray absorption property; it is used in cooking, body care
and traditional medicines. This tree is, however, uncultivated and collection of its nuts by rural
dwellers is threatened by increased urbanization with its accompanying land use pressure and the
need for fuel wood for rural households. There is also increased demand for shea products worldwide
necessitating the need for shea improvement strategies. At the apex of this improvement program
lies the need for germplasm collection, characterization, conservation and utilization. In order to
conserve elite shea materials amidst dwindling shea populations threatened by climate change, there
is a need to develop shea germplasm banks based on the representation of genetic and phenotypic
variation focusing on known traits. The objective of the study was to evaluate 282 shea accessions
for germplasm conservation and to determine the genetic diversity of the collected materials to
inform future collections and drive crop improvement strategies. Leaf traits were used to differentiate
and group the selected materials. Leaf length ranged between 16.83 cm and 30.85 cm, and leaf
blade length ranged between 12.28 cm and 20.68 cm. Petiole length varied between 5.53 cm and
10.2 cm and the blade to petiole ratio was from 1.41 to 2.69. Correlation studies revealed significant
negative correlation between the latitude of collection and all leaf traits measured. There was
significant positive correlation between blade length and petiole length (0.57), blade length and total
leaf length (0.87) and petiole length and breadth (0.49). The collected materials were grouped at
90% into two, based on the morphological descriptors studied. Three different approaches were
employed to genetically analyze the materials based on single nucleotide polymorphic markers (SNP).
A phylogenetic tree was constructed based on the SNPs generated; this grouped the materials into
three, with various subgroups. Principal coordinate analysis also produced three distinct groups
with groupings not based on geographical area of collection. Discriminant analysis of principal
components (DAPC) also confirmed three groupings. The genetic diversity of the collection was very
low (Hs) = 0.0406, which is an indication of potential inbreeding within the shea populations. To
conclude, there was higher variation within locations than between locations.
