Dioscorea sp. is a wild yam of the Gabonese forests. It is poorly studied because of its toxic and inedible tubers. The stems of this plant are however heavily consumed by several ethnic groups of Gabonese populations. The present work has been done to study some nutritional characteristics of these organs. The plant material was bought at the market from vendors in Moanda, and analyzed in the laboratory. The physicochemical and biochemical characters were studied using standard food analysis techniques. The results showed that the stems of this plant were rich in water (87.52%), ash (13.22%), and fiber (14.30%). From the biochemical point of view, the results revealed high levels of proteins (24.43%), carbohydrates (44.30%), vitamins C (2.38%) and polyphenols (0.78%). These different physicochemical and biochemical characteristics suggest that wild yam contains many nutritional and medicinal potentialities. It is therefore possible to foresee the domestication of this plant for a wider diet.

Phoma sabdariffae Sacc. (Sphaerioidaceae) is the main pathogenic fungus agent of roselle (Hibiscus sabdariffa L. var. sabdariffa), in Gabon. It does induce wet rot on every part of the infected plant's organs. This work was initiated to evaluate in greenhouse the impact of this pathogenic fungus agent on 13 roselle cultivars through the study of some morphological and biochemical parameters of the fruits. Morphological parameters evaluated have been fruit's number, weight and contamination rate. Concerning biochemical study, parameters measured have been roselle fruit's acidity, proteins and phenolics compounds levels. The results revealed that excepted 3 cultivars VV1, RV1 and RR1, Phoma sabdariffae caused significant decrease in the fruits number and weight of most of the roselle's cultivars. The decrease rates have been higher than 60% and 20% respectively. The improvement in acidity, protein and phenolics compounds levels were not significant, in contrary to those of the 3 cultivars above mentioned. In these 3 roselle's cultivars, biochemical parameters (pH, oxalic acid, ascorbic acid, proteins and phenolics compounds) levels have been superior to 20%. This work showed the disastrous impact of this fungus on the roselle's fructification and revealed that, some of the cultivars of roselle bright develop resistance mechanisms against Phoma sabdariffae.