Yams (Dioscorea spp) are tuber crops used as staple food in Africa because of their nutritional value. However agronomic constraints, phytosanitary problems and the lack of good healthy planting material restrict their production. In contrast to the inefficiency of traditional method of planting, tissue culture techniques allow to increase the multiplication and the rapid production of pathogenfree plant material. This work was undertaken to provide farmers in African countries with healthy microplants and microtubers as seeds. In vitro nodal segments of two varieties of local yams D. cayenensis-D. rotundata complex (cv. 'Singo', cv. 'Singou' and cv. 'Gnidou') were micropropagated on the modified medium of Murashige and Skoog. The morphogenesis, the growth of microplants and microtuber formation have been found to be controlled by external factors that act individually and synergistically. Addition of kinetin (2 mg l À1 ) to the culture media could reduce multiplication rate (node number) of some clones. An increase of the sucrose concentration from 3% to 5% induced no change in the multiplication and tuberisation parameters. An important reduction of the multiplication (shoot number, height and node number) and the tuberisation (tuber number and length) was observed with 8% sucrose. Multiplication (shoot and node number) was increased in the presence of jasmonic acid (10 mM). JA also induced an increase of tuber number in the absence of Kin. Multiplication of yam by in vitro growth of nodal segments is a way for rapid clonal multiplication and could allow solving the problem of lack of seed material faced by farmers. This method could also be used for multiplication of elite cultivars, independently of the growing season.

The effects of reducing sucrose level on tuber formation (% of cultures with microtubers), development (length and fresh weight of microtubers) and sprouting in yam Dioscorea cayenensis-D. rotundata complex in vitro were investigated. Only 29% of the explants showed tuber formation after 3 weeks in the presence of 1% sucrose in contrast to 100% with 3%. After 120 days of culture, the length and the weight of the tubers obtained in the presence of 1% sucrose were less than with 3% sucrose. Addition of sorbitol to keep osmolarity at the same level did not restore normal rate of tuber formation. Similar results were obtained with the use of reduced fructose or glucose level. Microtuber sprouting was also affected by sucrose level incorporated into the tuberisation medium. Tubers obtained on reduced sucrose level sprouted later and the increase of osmolarity with sorbitol did not restore normal sprouting. The bigger tubers obtained on high sucrose media could contain more carbohydrate reserves that could partially explain a higher sprouting rate. These results can be used for optimising in vitro conditions for mass production of microtubers in yam and especially in Dioscorea cayenensis-D. rotundata complex, a very important species in West Africa. They specially showed the importance of tuberisation conditions on precocity of tuberisation, on tuber length and weight and on their further sprouting.

Plant biology and pathology/Biologie et pathologie ve ´ge ´tales Effects of storage conditions on sprouting of microtubers of yam (Dioscorea cayenensis-D. rotundata complex) Effets des conditions de conservation sur la germination des microtubercules d'igname (complexe Dioscorea cayenensis-D. rotundata

Le scolyte des baies de café (Hypothenemus hampei Ferrari) limite fortement la production caféière au Sud-Est du Gabon. La présente étude vise à tester l'effet des extraits végétaux de Jatropha curcas L. et Tabernanthe iboga Baill. sur ce ravageur, comparativement à un insecticide chimique dont la matière active est l'Endosulfan. Suite au dénombrement et à l'élevage des scolytes, des extraits bruts de T. iboga et de J. curcas ont été mis au contact des insectes. Une évaluation des dégâts a suivi pour estimer les taux d'attaque des cerises du caféier. L'étude révèle l'action de ces extraits sur la mortalité et la réduction des dégâts causés par les scolytes. En effet, les extraits des feuilles de J. curcas non dilués tuent 100% des scolytes au même titre que l'insecticide organophosphoré dénommé Sultan 350 EC. Par ailleurs, les extraits des feuilles de T. iboga non dilués exercent une action répulsive sur le scolyte et les cerises sont protégées jusqu'à 66,67%. Ces extraits obtenus des végétaux naturels du Gabon constituent une alternative certaine aux insecticides de synthèse qui sont devenus inefficaces contre le scolyte des baies de café. © 2015 International Formulae Group. All rights reserved.Mots clé : Extraits végétaux, Jatropha curcas L., Tabernanthe iboga Baill., scolyte, cerises du caféier, mortalité. Effect of the extracts of Jatropha curcas L. and Tabernanthe ibogaBaill. in the fight against the coffee berry borer (Hypothenemus hampei Ferrari) in the South-East of Gabon ABSTRACTCoffee berry borer (Hypothenemus hampei Ferrari) strongly limits the coffee production in the SouthEast of Gabon. The present study aims to testing the effect of Jatropha curcas L. and Tabernanthe iboga Baill.P. NGUEMA NDOUTOUMOU et al. / Int. J. Biol. Chem. Sci. 9(6): 2764-2775, 2015 2765 plant extracts on this devastating insect, compared to a synthetic insecticide whose active compound is Endosulfan. After the enumeration and the breeding of the borers plant extracts of T. iboga and J. curcas were put in contact within sects. An evaluation of the damage and the estimation of the rates of attack of berries were under taken. The study reveals the action of these extracts on the mortality and the reduction of the damage caused by the borers. Indeed, the undiluted leaf crude extracts of J. curcas kill 100% of the insect similar to the rate observed using the insecticide « Sultan 350 EC ». In addition, the undiluted leaf crude extracts from of T. iboga exert a repulsive action on the borer and the berries are protected up to 66,67%. These extracts obtained from the natural plants of Gabon constitute an alternative to the synthetic insecticides which became ineffective against the coffee berry borer.

Tuberisation was obtained in vitro on yam (Dioscorea cayenensis-Dioscorea rotundata complex). The effect of exogenous polyamines on tuber formation and development (length and weight of microtubers) was investigated and discussed in relation with changes in endogenous polyamines. Application of exogenous polyamines, inhibitors of their metabolism, and polyamines precursors in various concentrations positively affected microtuber formation by yam nodal cuttings and their further development. In control conditions, 3 wk are needed to obtain 100% of tuberisation. With low concentrations of putrescine (10 −5 or 10 −6 M), tuber formation occurred earlier. Polyamine endogenous level and metabolism can be significantly affected by exogenous polyamines, but modifications of endogenous free polyamines could not be directly correlated to the tuber formation process. Increases in endogenous putrescine and auxins were observed in tubers showing a better development in the presence of putrescine. These results can be used for optimising in vitro conditions for mass production of larger microtubers of the D. cayenensis-D. rotundata complex.