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 ...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, above-ground 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 of 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.展开更多
Differences in transpiration and leaf water potential （LWP） in relation to cassava yield were investigated along inland valley toposequence in a 4×4 Latin square design. The landrace with the highest transpirat...Differences in transpiration and leaf water potential （LWP） in relation to cassava yield were investigated along inland valley toposequence in a 4×4 Latin square design. The landrace with the highest transpiration rate and lowest LWP yielded the lowest, while TMS 91/02324 and TMS 91/02327 with intermediate rate and highest LWP yielded the highest, indicating that high transpiration rate associated with low LWP reduced yield. Transpiration was lower in the fringe with deeper water table than valley bottom at deep water table site, while at shallow water table, it was higher in the fringe than valley bottom, suggesting that drought and excess moisture reduced transpiration. LWP and water table depth correlated negatively indicating that shallow water table reduced transpiration by reducing LWP. Transpiration increased and LWP decreased as radiation, leaf temperature and vapour pressure deficit increased and differences in these microclimatic conditions caused differences in the two processes between sites, years and time of day. Under mild water stress, transpiration and LWP were higher in the afternoon than the morning, but the reverse occurred under severe stress. TMS 91/02324 and TMS 91/02327 had the highest LWP under severe stress, indicating their higher drought tolerance than the other cultivars.展开更多
文摘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, above-ground 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 of 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.
文摘Differences in transpiration and leaf water potential （LWP） in relation to cassava yield were investigated along inland valley toposequence in a 4×4 Latin square design. The landrace with the highest transpiration rate and lowest LWP yielded the lowest, while TMS 91/02324 and TMS 91/02327 with intermediate rate and highest LWP yielded the highest, indicating that high transpiration rate associated with low LWP reduced yield. Transpiration was lower in the fringe with deeper water table than valley bottom at deep water table site, while at shallow water table, it was higher in the fringe than valley bottom, suggesting that drought and excess moisture reduced transpiration. LWP and water table depth correlated negatively indicating that shallow water table reduced transpiration by reducing LWP. Transpiration increased and LWP decreased as radiation, leaf temperature and vapour pressure deficit increased and differences in these microclimatic conditions caused differences in the two processes between sites, years and time of day. Under mild water stress, transpiration and LWP were higher in the afternoon than the morning, but the reverse occurred under severe stress. TMS 91/02324 and TMS 91/02327 had the highest LWP under severe stress, indicating their higher drought tolerance than the other cultivars.
