Insect pollinator dependence of shea (Vitellaria paradoxa C.F. Gaertn.) in the Guinea Savanna zone of Ghana

Abstract

Shea (Vitellaria paradoxa C.F. Gaertn.) is a multipurpose tree species indigenous to the Sudano Sahelian zone of Africa and occurs as the most abundant economic tree species in northern Ghana. The edible oil (shea butter) extracted from shea kernel is ranked as the most economic product of the species. Although fruit set and yield of shea are known to be influenced by insect pollination, the actual contribution of insect pollinators to its reproductive success has rarely been studied. This study estimated the percentage insect pollinator dependence and monetary value of insect pollination per bag of shea kernel (85 kg) in the Guinea savanna zone. Open pollination and insect exclusion treatments were applied to the flowers of 18 randomly selected matured shea trees and observed from the onset of flowering to fruit maturity. Proportion of total production value attributed to insect pollination approach was used in estimating the monetary value of pollination per bag of shea kernel with the average market price as proxy. The study revealed an insect pollinator dependence of 77% and 73% for fruit set and dry kernel yield, respectively. Mean number of fruit set per inflorescence varied significantly between insectexcluded and open-pollinated inflorescences (p < 0.05). The monetary value of insect pollination was estimated at GH₵ 73.21 (US$ 18.67) per bag of kernel as of August 2016. Shea is a high insect pollinator-dependent species and the conservation of insect pollinators would be critical to the sustainability of yield.

Assessing the biodiversity and the impact of pollinators on carob production

“…The positive effect of pollination is not limited to carobs, for instance Nasare et al [48] recorded heavier shea kernels under open pollination compared with bagged inflorescences. Similarly, tomatoes from non-bagged flowers were larger, heavier, and with more seeds compared with those produced by bagged flowers [49].…”

The Current State of Knowledge of Shea Butter Tree (Vitellaria paradoxa C.F.Gaertner.) for Nutritional Value and Tree Improvement in West and Central Africa

“…The flower is hermaphroditic and actinomorphic, enveloped at the base of its peduncle by a very small bract [41,42]. The creamy white flowers, very fragrant and honey-bearing, are carried by long pedicels (22-25 cm) (Figure 1a) [43][44][45].…”

“…The flower is hermaphroditic and actinomorphic, enveloped at the base of its peduncle by a very small bract [41,42]. The creamy white flowers, very fragrant and honey-bearing, are carried by long pedicels (22-25 cm) (Figure 1a) [43][44][45]. The shea fruit can be described as a globose to ellipsoid berry, measuring 4-5 cm × 2.5-5 cm, with a weight of 20-30 g. The fruit appears to be a yellow, green, or yellow berry with thick pulp with one oval or round red-brown seed-the shea nut.…”

In vitro regeneration of Vitellaria paradoxa from shoot tip explants

“…The use of grafting as a cultivation method is only recently yielding some results, though they are limited (Sanou and Lamien, 2011 ; Amissah et al, 2013 ). Pollination in shea is carried out by insects or wind, and thus produced plants are highly heterozygous (Nasare et al, 2019 ). Moreover, the long vegetative phase of the tree (between 10–15 years) in addition to the steady degradation to the ecological system has led to the destruction of wild, isolated shea trees or groves, hence posing a threat to commercialscale propagation and domestication of shea tree (Honfo et al, 2014 ; Bello-Bravo et al, 2015 ).…”