Etude de la variabilité phénotypique de Megaphrynium macrostachyum (Benth.) Milne-Readh. pour une gestion durable

Abstract

Forests are natural environments with high biological diversity. Among these, there are minor food plants, also called "hidden crops", which have been neglected for a long time but are still diversely used by local populations. This is the case of Megaphrynium macrostachyum, a non-timber forest product (NTFP) belonging to the Marantaceae family. This plant is exploited in several value chains in certain localities in the Center and Littoral Regions of Cameroon. For this reason, its leaves are regularly and intensively harvested and marketed, which could make the species vulnerable in its ecological environment in the long term, hence the need to focus on this "hidden crop". The main objective of this study is to evaluate the phenotypic diversity of M. macrostachyum in order to undertake its domestication. Thus, the plant material used consisted of 165 accessions of M. macrostachyum, chosen in five localities in the agro-ecological zones (AEZ) IV and V of Cameroon, at a rate of 33 samples per locality. The choice of sampling was made using the technique of exhaustive random sampling, which consists of selecting individuals in such a way that all have the same probability of being part of the sample, ethnobotanical survey with individual and semi-structured interviews and direct observations in the field have been also done with 102 merchants. Megaphrynium macrostachyum is more used in the food (UA = 99%) and medicinal (UM = 61,85%) domains. Its marketing is a profitable activity according to 99% of respondents. This activity provides an average gain of 211.1 FCFA per average package of 57 leaves, with an average purchase price of 147 F CFA and a sale price of 246 F CFA. The major difficulties encountered by the sector are the transport (48,23%) and the rotting of the leaves (27,06%). The actors involved in the sector are mostly single (48%) and married (34%), their education level being mainly secondary (47%) and primary (46%). Young women being the main providers (84,15%) and the Bassa community the main source of supply for the product (55,31%). Two phenological phases were identified, namely the floral phase which lasts from May 17 to June 29 and includes four stages of development: initiation of the main floral bud (fl1), blooming of the main bud into secondary buds (fl2), blooming of secondary buds into flowers (fl3) and senescence of flowers (fl4). The fruiting phase lasts from June 15 to August 28 and also includes four stages: fruit set (fr1), fruit development (fr2), fruit maturation (fr3) and fruit ripening (fr4), for a total duration of 64 to 84 days. No significant difference was noted in terms of the duration of each phase and the different stages of fruit development, though a two-week delay was observed in flowering between the two AEZ. Statistical analysis showed significant differences between the variables studied in the two agro-ecological zones (diameter at the collar, length, width, surface and number of secondary nerves of the limb) except for the length of the stem. Variability was confirmed xxix across all variables studied through the Coefficients of Variation (CV) which were all higher than 20%. Principal Component Analysis (PCA) did not allow for the grouping of accessions by origin zone, but rather showed a dispersion of individuals on either side of the 2 planes. Hierarchical Ascending Classification (HAC) showed significant variability between accessions with the formation of 3 groups (clusters 1, 2 and 3). The parameters of the petiole (diameter at the collar and length of the petiole) and leaf surface were the most discriminant phenotypic characters for assessing phenotypic variability within the species. Two modes of multiplication exist in the species, the vegetative mode which takes place through indefinite branching of a rhizome from which several vertical axes (monopodes) develop, and which is the preferred mode of development of the plant. On the other hand, seed multiplication of the plant showed satisfactory results with a seed germination rate of 81.66%. The morphological growth parameters also showed good plant development up to 12 months of age, with a mean collar diameter of 0.41 mm, a mean plant length of 69.72 cm and a mean leaf surface area of 797.22 cm2. The results of this study constitute a database for a potential genetic improvement program for the accessions of M. macrostachyum exploited by local communities, as well as a way for participatory domestication.