Weed suppression ability of upland rice under low-input conditions in WestAfrica

Weeds are a major constraint to upland rice production in west Africa. The objectives of this investigation were to study differences in weed suppress ion ability among upland rice cultivars and to determine the morphological traits involved. Twelve contrasting cultivars, including West African indig enous Oryza glaberrima (Steudel) lines and traditional and improved O. sati va L., were cultivated under natural weed competition and low-input conditi ons in Cote d'Ivoire in two seasons. Significant differences between cultiv ars were observed in weed biomass at 100 days after seeding (DAS) in 1994 a nd 1995, indicating differences in their competitive ability. Weed biomass was negatively correlated with rice root growth at early growth stages and with rice shoot and root growth at later growth stages. Across cultivars, g rain yields with a single hand-weeding were 60% in 1994 and 49% in 1995 of those in plots that were weeded regularly. High grain yields in weedy plots were associated with low weed biomass. IG 10, an O. glaberrima cultivar, w as the most competitive against weeds.