Observations on the susceptibility of Oryza sativa and resistance of Oryzaglaberrima to the cyst nematode (Heterodera sacchari) and the influence ofweed management in upland rice in Ivory Coast

The population density of the cyst nematode, Heterodera sacchari, on Oryza sativa and three O. glaberrima cultivars was assessed in a pot test and in the field under two levels of weed management, weed-free and hand weeded, o nce 43 days after sowing. Similar numbers of cysts developed on both specie s of rice, but cysts from O. glaberrima were smaller and contained fewer eg gs, resulting in significantly lower population densities of H. sacchari. T he successful cyst nematode development (equivalent to that on susceptible cultivars) albeit of less fecund females, could reduce selection pressure f or virulence on H. sacchari resistant cultivars. Population densities of H. sacchari were significantly higher on weed-free plots, suggesting that the better rice growth from the reduced interspecific competition in weed-free plots facilitated an increased multiplication of H. sacchari. in declining order of abundance, the dominant weed species present were: Eleusine indic a, Digitaria horizontalis, Euphorbia heterophylla and Ageratum conyzoides, all were non-hosts of H. sacchari.