Diversity of the sheanut tree (Vitellaria paradoxa CF Gaertn.) in ghana

The Sheanut tree (Vitellaria paradoxa C.F. Gaertn.) is highly valued for oi l obtained from its seeds and frequently maintained in the semi-arid parkla nds of sub-Saharan Africa from Senegal to Uganda. Although variation has be en noted for V. paradoxa subsp. paradoxa, few studies have been undertaken on patterns of phenotypic or genotypic diversity. Results are presented fro m 294 accessions collected in Ghana, using easily quantifiable morphologica l parameters. Productive mature trees varied from shrubby multi-stemmed ind ividuals (height <5 m) to 30-m straight-boled trees with high compact canop ies. The leaf lamina (tree mean +/-% coefficient of variation of total mean ) varied from 9.2 to 22.5 cm (+/- 15.0%); seed length from 1.74 to 3.74 cm (+/- 11.7%); and fat content from 29.1 to 61.9% of dry kernel weight (+/- 9 .4%). Clinal trends significantly correlated with location parameters that in turn related to environmental variation. Population variation of seed ch aracteristics increased to the Northeast, perpendicular to the annual movem ent of the inter-tropical convergence zone. It is proposed that this is a c onsequence of past climatic changes, coupled with a lack of methodical sele ction for seed type when trees are maintained on agricultural land. Isozyme analysis revealed moderate to high levels of heterozygosity (He 0.2142) an d high geneflow (Fst = 0.0124, Nm = 19.9), supporting results obtained from morphological studies. Isozyme and multivariate morphology analyses showed similar but weak geographical separation patterns.