Domestication of Irvingia gabonensis:: 2.: The selection of multiple traits for potential cultivars from Cameroon and Nigeria.

Ten fruit and kernel traits were assessed in 24 fruits of each of 152 Irvingia gabonensis trees in three distinct populations in west and central Africa [2 populations of non-planted trees in Cameroon: Nko'ovos II (21 trees) and Elig-Nkouma (31 trees) and 1 population of planted trees in Nigeria: Ugwuaji (100 trees)]. Strong relationships were found between fruit weight and other fruit traits (e. g. flesh weight [r(2) = 0.99: P < 0.001], fruit length [r(2) = 0.74-0.83: P < 0.001], fruit width [r(2) = 0.77-0.88: P < 0.001]). In contrast, relationships between kernel weight and other kernel/nut traits (e. g. shell weight and nut weight) were found to be weak [r(2) = 0.009-0.37, P = 0.058-0.001], with the exception of nut weight at Nko'ovos II (r(2) = 0.65, P < 0.001). Relationships between fruit and kernel traits (fruit mass v. kernel mass, fruit mass v. shell mass, flesh mass v. kernel mass, nut mass v. fruit mass and flesh depth v. kernel mass) were found to be very weak. This indicates that domestication through the selection and vegetative propagation of multiple-trait superior phenotypes is unlikely to be able to combine good fruit characteristics and good kernel characteristics within cultivars. Consequently, domestication activities should independently focus on ideotypes representing: 'fresh fruit' traits, and 'kernel' traits, that combine high values of the different fruit and kernel characteristics respectively. Evidence from this study indicates that selection of the three trees closest to the fruit ideotype per village as the mother plants for vegetative propagation and cultivar development, should give village level gains of 1.3 - 2-fold in fruit mass, and up to 1.5-fold in taste. Similarly for the kernel ideotype, selection of the three trees with the best fit would give potential gains in kernel mass of 1.4 - 1.6-fold.