Observations on the community dynamics of plant parasitic nematodes of rice in Cote d'Ivoire

The population dynamics of nematode communities were studied during a rice cropping season in 22 fields in the humid forest zone of Cote d'Ivoire. Rai nfed upland, hydromorphic, and lowland rice fields were examined during the 1996 growing season and compared to nematode communities in adjacent undis turbed forest and vegetation. Forest clearance and burning had little immed iate influence on nematode species diversity. Thirty days after the introdu ction of rice, nematode species diversity across ecosystems was reduced by 57% to seventeen species. At harvest, species diversity was 55% lower than in adjacent forest and vegetation. With progression of the season, a small percentage of nematode genera became numerically dominant, while the greate r proportion of nematode genera were present at low mean intensity. At harv est Meloidogyne spp. were numerically dominant in upland rice and Hemicycli ophora oostenbrinki numerically dominant in hydromorphic rice, accounting f or 74 and 75% of total mean intensity in upland and hydromorphic ecosystems , respectively. Lowland rice communities were characterised by low nematode intensity and low species diversity. Dominant species at harvest were Heli cotylenchus spp. (52% of total mean intensity) which were undetected at sow ing. Other nematodes which persisted under rice at low mean intensity in va rious ecosystems were Trichodorus eburneus, Xiphinema hygrophilum and Praty lenchus brachyurus.