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. Rainfed upland, hydromorphic, and lowland rice fields were examined during the 1996 growing season and compared to nematode communities in adjacent undisturbed forest and vegetation. Forest clearance and burning had little immediate influence on nematode species diversity. Thirty days after the introduction 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 greater proportion of nematode genera were present at low mean intensity. At harvest Meloidogyne spp. were numerically dominant in upland rice and Hemicycliophora oostenbrinki numerically dominant in hydromorphic rice, accounting for 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 Helicotylenchus spp. (52% of total mean intensity) which were undetected at sowing. Other nematodes which persisted under rice at low mean intensity in various ecosystems were Trichodorus eburneus, Xiphinema hygrophilum and Pratylenchus brachyurus.