No abstract

A survey of plant parasitic nematodes of rice was made in Ghana between 1994-1997. Fifty-one species in 29 genera were found in 145 fields from upland, hydromorphic, rainfed lowland and irrigated lowland ecosystems in the savannah and forest agroecological zones. Eighteen species were endoparasites of roots. In upland/hydromorphic rice fields in the savannah zone Pratylenchus spp. (80% of fields) and an undescribed species of Ditylenchus (78%) were most prevalent, whilst Coslenchus franklinae (84%) and Helicotylenchus spp. (76%) were most prevalent in the forest zone fields. Maximum population densities encountered were 960 C. franklinae per 100 ml soil and 700 Ditylenchus n. sp. per g root. In the savannah zone Hirschmanniella spp. (100%) were more prevalent than other nematodes in lowland rice, but in the forest zone Xiphinema bergeri (71%) was the most prevalent nematode in lowland rice. Occurrence of nematode species was different in different agroecological zones and rice ecosystems. There was no relationship between rice plant height and nematode population densities in crops close to harvest time in upland/hydromorphic fields in the savannah zone. Predominance des nematodes phytoparasites sur le riz au Ghana et discussion sur leur importance - Une prospection concernant les nematodes associes au riz a ete effectuee au Ghana de 1994 a 1997. Cinquante-et-une especes appartenant a 29 genres ont ete trouvees dans 145 rizieres de plateau, de bas-fonds, pluviales ou irriguees, tant en savane que dans des zones agroecologiques forestieres. Dix-huit especes sont des endoparasites racinaires. Dans les rizieres de plateau ou de bas-fonds en zone de savane Pratylenchus spp. (80% des rizieres) et une espece non encore decrite de Ditylenchus (78%) sont les plus abondants, tandis que Coslenchus franklinae (84%) et Helicotylenchus spp. (78%) le sont dans les rizieres de zone forestiere. Les densites maximales de population observees concernent C. franklinae (960 per 100 cm3 de sol) et Ditylenchus n. sp. (700 per 1 g de racines). Hirschmanniella spp. etaient plus abondants (100 %) que les autres nematodes dans les rizieres de bas-fonds de savane, tandis c'etait Xiphinema bergeri (71%) dans ce meme type de rizieres en zones forestieres. La presence des differentes especes de nematodes varie suivant la zone agroecologique et l'ecosysteme de la riziere. Il n'y a pas de relation entre la hauteur des plants de riz et la densite des populations de nematodes pour des cultures proches de la recolte dans les rizieres de plateau ou de bas-fonds situees en savane.