Résumé
The cyst nematode, Heterodera sacchari, is emerging as a potentially serious pathogen of rice in West Africa, where it is widespread. Cropping practices regionally are becoming more intensified in response to consumer demands. The effects of this change on the pest potential of H. sacchari has been studied at WARDA. Under hydromorphic and upland conditions the nematodes can affect crop establishment and considerably reduce yield. Detection of 10 juveniles L-1 soil at sowing will lead to yield losses. Delayed hatching of these nematodes from cysts, due to dormancy, and relationships with other extraneous factors complicate yield loss assessment, however. Field studies conducted during 1997 at WARDA showed that under low water availability in sandy soil, damage to a nematode susceptible Oryza sativa cv. IDSA6, is exacerbated. Visual symptoms of drought and physiological aspects of stomatal conductance, water potential, relative water content, and leaf chlorophyll content were significantly affected (P<0.001) in plots with a mean density of 467 nematodes g-1 root fresh weight at 81 DAS, as compared with plots containing a mean density of 14 g-1, leading to near total yield losses. It is suggested that the presence of H. sacchari significantly enhances the effects of drought and drought-related production losses which will complicate models predicting crop damage by either drought or nematodes. The potential for resistance in O. glaberrima and in hybrids newly developed at WARDA between O. glaberrima and O. sativa are discussed. (Texte intégral)