Abstract:
Shea trees (Vitellaria paradoxa C. F. Gaertn.) are classified locally into several folk or
ethno-varieties by farmers in Uganda. It is, however, not clear whether this folk
classification is supported by genetic differentiation between ethno-varieties.
Genetically linked traits from folk classification are useful in conservation and breeding
programmes.Atotal of 118 individual shea trees constituting 28 ethno-varieties sampled
from three farming systems of Uganda were analysed using microsatellite markers. The
number of alleles amplified per microsatellite locus ranged from 6 to 13 with an average
of 9.5, with a total of 106 alleles identified. Observed (Ho) and expected heterozygosity
(He) per locus ranged from 0.366 to 0.934 and 0.580 to 0.840, respectively. Mean Ho and
He values for all loci across all ethno-varieties were 0.633 and 0.727, respectively.
Analysis of molecular variance indicated that most of the variation (86.28%) occurred
within individual trees; 11.25% was found among individual trees within ethno-varieties
while 2.47% was found among ethno-varieties. The in-breeding index ( f ¼ 0.130),
fixation index (uP ¼ 0.025), gene flow value (Nm ¼ 6.56) and cluster analysis show that
all shea tree ethno-varieties were a single out-crossing population with very low genetic
differentiation and high gene flow. The low differentiation in shea tree ethno-varieties
was most likely due to the utilization of non-genetic traits in folk classification.
However, while ethno-variety genetic structure was very weak, overall spatial
population structure indicated the presence of three populations (West Nile, Northern
and Teso). The West Nile population was more distantly related to the other two most
likely due to isolation barriers such as the Rift Valley, Lake Albert and River Nile.