Agroecological variation in the fruits and nuts of shea butter tree (Vitellaria paradoxa C. F. Gaertn.) in Nigeria

Abstract

A basic understanding of the relationships between key phenotypic characters of the shea butter tree is considered a crucial step to its genetic improvement. As such fruit samples of the shea butter tree, Vitellaria paradoxa, were collected from nine locations in July, 2006, to determine the fruit and nut characteristics of the species. The choice of the locations was informed by the need to have as broad a picture of the trait diversity as possible. The nine locations covered were Akwanga, Ilorin, Lokoja, Makurdi, Minna (in the Southern Guinea Savanna), Jalingo, Kachia (in the Northern Guinea Savanna), Kano and Yola (in the Sudan Savanna), recognized as the main shea butter tree belt in Nigeria. Analysis of variance indicated significant (P < 0.05) variations in fruit and nut traits across agro-ecologies and specific locations (representing individual accessions). The Northern Guinea Savanna accessions had higher values for nut weight, nut length kernel weight and fruit weight. The Southern Guinea Savanna fruits were, however, superior in percent pulp weight. Nuts sourced from Akwanga were comparatively heavier and longer, had wider diameters, heavier kernels and higher percent testa weights which did not differ from those of Minna. Also fruits from Akwanga had significantly (P < 0.05) higher values for fruit length, fruit diameter, fruit weight and pulp weight. The Lokoja accession was superior to the rest in percent pulp weight, but it recorded least nut weight and nut length values. Nut shape index varied from 2.3 (Makurdi) to 1.5 (Jalingo). Nuts from Akwanga, Jalingo and Kachia had wide variation in nut weight in contrast to those from Lokoja, Makurdi and Yola (that were relatively similar). Fruit length had significantly (P < 0.05) positive relationship with pulp weight, fruit weight and fruit diameter. Nut diameter, however, had a negative relationship with percent pulp weight. A strong influence of some environmental variables on certain phenotypic traits was detected. Principal components analysis indicated nut weight, nut shape index, percent pulp weight and fruit shape index as the key discriminant variables for grouping shea butter fruit and nut in Nigeria. Results of this study indicated considerable diversity in fruit and nut traits of the shea butter tree in Nigeria, suggesting the possibility of selection for desirable traits.