Variation in phenotypic traits of high oil yielding and early maturing shea trees (Vitellaria paradoxa) selected using local knowledge

Abstract

Shea trees (vitellaria paradoxa) grow in West Nile, Teso, Lango and Acholi subregions of Uganda existing in different forms called enthnovarieties. Farmers from each of these subregions use phenotypic characteristics to differentiate one ethnovariety from the other.  We conducted phenotypic characterization of shea trees identified by farmers as high oil yielding and early maturing and verified the farmers’ descriptors with standard phenotypic characterization.  The study was conducted in the districts of Amuru, Arua, Katakwi, Moyo and Otuke between May and June 2017. One hundred eighty mature shea trees were purposively sampled from the five districts based on local knowledge.  Descriptive statistics was then used to determine the variation among the different shea tree phenotypes characterized using standard descriptors. Twenty-seven ethnovarieties were recorded using farmers’ descriptors which were later on reduced to sixteen phenotypic traits using standard phenotypic descriptors related to fruit shapes, texture and kernel color. Variation in the kernel weights, fruit length and fruit width were significant (p < 0.05) and the shea fruit and seed width were highly correlated (78.6%) to their weights. We identified significant variation in shea trees within sites and fruit and seed weights between sites (p ≤ 0.001). Although variability within sites was significant, most parameters (height, diameter at breast height (dbh at 1.3 m), crown shape and height at first branching) were not. Shea fruit/kernel traits are important in characterizing varieties since they exhibit different forms across the sites since tree phenotypic attributes do not vary from location to location in Uganda. This lack of variability of ethnovarieties across the shea belt in Uganda is important in breeding for traits that can be acceptable by all the communities within the shea growing regions. The different shea ethnovarieties are therefore important in influencing policy decisions on their conservation.