Cassava is a considerable source of food and income for the rural community of the south of Chad. Despite the importance of the diversity of cultivars in situ, their morphological traits and agronomic performance are under investigated. The aim of this study is to characterize and analyze the variability structure of the cassava's germplasm. Fifty nine cultivars collected from five main cassava growing regions, were evaluated by forty five agro-morphological descriptors in a Fisher design replicated three times. Data were collected at three, six, nine and twelve months after planting. High phenotypic variability was shown within the collection for the color of apical leaf, vein leaf, petiole, roots and pulp. The same case was observed for the root peduncle, the shape of the central leaflet and the root, the cortex root thickness and the texture of root epidermis. Significant to highly significant differences were observed for all the quantitative traits. High variability were shown for the size of the leaf lobe, petiole length, plant height, root number and length, harvest index, aboveground biomass and fresh root weight. Positive correlations were found between the leaflet and leaf lobe number. Fresh root weight was also positively correlated to the root number, length and diameter. Principal component analysis (PCA) on quantitative variable revealed four groups with two * Corresponding author. D. Nadjiam et al. 480of them containing performant cultivars: Group II with small root, high potential yield but less leaflet and leaf lobe and group III characterized by some cultivars with high productivity, more leaflet and leaf lobe, more and bigger roots. At regional level, significant differences were shown within cultivars which were discriminated in relation to their origin region by the number of the leaf lobes. The better cultivars and the interesting traits could be used to improve cassava production in Chad.

REMERCIEMENTS Nous adressons nos sincères remerciements aux responsables de l'ITRAD, au PRASAC et à l'UE pour la bourse qui nous a été accordée pour ce travail. RESUMEDans les petites exploitations familiales, les paysans détiennent un nombre important de cultivars de manioc inexploités par la recherche. L'objectif de cette étude est d'évaluer le niveau de la diversité du manioc et d'en analyser les pratiques locales de gestion. Une enquête suivant une approche participative avec des questionnaires a été conduite auprès de 636 paysans dans 43 villages. Une importante diversité variétale a été révélée par l'indice de Shannon (3,38). Soixante-quinze noms vernaculaires ont été inventoriés. Des différences hautement significatives ont été observées pour le nombre de cultivars qui varie de 2 à 12 par village (6 en moyenne). La variation entre ménages est faible, 1 à 4 cultivars (2 en moyenne). Le nombre de cultivars disparus varie de 1 à 14 (3,81 en moyenne) par village. La perte de la diversité est en moyenne de 18,20% et varie entre 11% et 50% selon les villages. Les paysans identifient les cultivars à partir des feuilles et tiges. La productivité, le goût et la grosseur des tubercules sont les critères prioritaires de sélection. Les échanges des boutures se font entre paysans locaux (60,84%) et par des introductions individuelles (37,43% Farmer management of cassava cultivars (Manihot esculenta Crantz)in the South of Chad D. NADJIAM et al. / Int. J. Biol. Chem. Sci. 10(3): 1098-1113, 2016 1099 ABSTRACTFarmers possess in their fields, many cassava cultivars which are unexplored by the research. The aim of this study is to assess their diversity and to analyze their traditional management. A total of 636 farmers selected from 43 villages, were surveyed using questionnaire and participatory rural appraisal. ShannonWeaver diversity index (H) revealed an important level of diversity of 3.38 in the study zone. Seventy-five (75) vernacular names were recorded. Highly significant differences were observed for the number of the cultivars that ranges from 2 to 12 per village (6 on average). At household level, the variation is low and ranged from 1 to 4 cultivars (2 on average). The number of disappeared cultivars range from 1 to 14 (3.84 on average) per village. The average rate of diversity loss is 18.20% and ranging from 11% to 50% per village. Farmers use leaves and stems to identify cultivars. High yield root, taste and large sized rate were the farmer preferred criteria. The exchanges of the stems are done among local farmers (60.84%) and by individual initiatives (37.43%). This knowledge will be integrated in the breeding program.