Study of the Effects of Height, Defoliation Treatment and Light on the Growth of Irvingia gabonensis (Irvingiaceae) and Ricinodendron heudelotii (Euphorbiaceae) Regrowth in a Nursery at Soubre in Southwest Cote d’Ivoire

Abstract

Irvingia gabonensis and Ricinodendron heudelotii are two species of multipurpose trees found in the dense tropical forests of Africa. However, they are under strong pressure due to human activity because of the extension of agriculture, particularly cocoa farming in Côte d’Ivoire; the importance of food, medicine, and especially the economic value of almonds of these two species. Unfortunately, these two species are facing difficulties in natural regeneration related to the seed coat resistance of their seeds and many other constraints, thus threatening their sustainable conservation. This study conducted in Soubré in the southwest of Côte d’Ivoire aims to contribute to the production of vigorous seedlings of these two species in a nursery from regrowth with a view to their domestication through agroforestry. To do this, shoots of these two species of different height classes ([0 - 15], [15 - 30] and [30 - 50] cm) were collected and underwent a defoliation treatment with 4 modes including 0, 2, 3, and 4 leaves. They were then grown in two different light environments, one illuminated and the other shaded. Their growth was then monitored to determine the effect of sampling height, defoliation treatment and light on the recovery and growth of wildlings in the nursery. The results showed that R. heudelotii plants grown in a shaded environment with a height of between 0 and 15 cm and with the 4-leaves dressing mode showed the best growth. At Irvingia gabonensis , the regrowths with heights between 15 and 30 cm, with a cover type of 0 leaves, and those in the height class of 30 to 50 cm with 2 leaves showed the best growth in a lit environment. In conclusion, this study shows that the optimal conditions for survival and growth of regrowth are not the same for all species. The proper development of the plants after transplantation requires specific morphological, physiological, and ecological conditions for each species. Furthermore, the use of regrowth from these two species can be an alternative to the production of their plant material given the constraints of germination. Considering their economic, environmental, and ethnobotanical interest for the populations, it is necessary to ensure their sustainable conservation by integrating them into agroforestry programs.