Résumé
Crosses of Asian rice, #Oryza sativa#, with African rice, #Oryza glaberrima#, aim at reducing the trade-offs between yield potential, weed competitiveness and drought resistance. Research at WARDA shows that the morpho-physiological characteristics of these two rice groups are quite different. The African rice, #O. glaberrima#, is weed competitive, characterized by high vegetative growth rate (shoot and root), resulting from low phyllochron, a large specific leaf area, a high light extinction coefficient and increased partitioning of assimilates to leaf blades. This high specific leaf area is associated with a low stomatal density and a low chlorophyll content; the rapid vegetative growth rate with the high light extinction coefficient maximizes the evapotranspirative surface. In addition, carbon-isotope discrimination (CID) studies show high values for #O. glaberrima# like the lowland #O. sativa# subsp. #indica# in contrast to upland rice (#O. sativa# subsp. #japonica#). Therefore, #O. glaberrima# uses a large quantity of water. Although high vegetative growth (shoot and root), large specific leaf area, and poor water use efficiency (CID) are not good characteristics for drought adaptation, #Oryza glaberrima# does show very good adaptation to the drought environnement (low stomatal density, fast leaf rolling, good maintenance of plant water status by the control of stomatal conductance). These differences imply that there are different physiological mechanisms for drought avoidance in #O. sativa# and #O. glaberrima#. It is important for the development of drought-adapted interspecifics that we know the physiological drought mechanisms used by #O. glaberrima#. (Texte intégral)