Assessment of the importance of individual plant-parasitic nematode species in a community dominated by Heterodera sacchari on upland rice in Cote d'Ivoire

In temperate climates, densities of plant-parasitic nematodes at or shortly before sowing are a useful predictor of their damage potential. Re-examination of data from nematode communities on upland rice in Cote d'Ivoire showed that interpretation of nematode pest potentials and the damage caused by either individual species, or by the community as a whole, is less simple. The numerical proportion of individual nematode species within a plant-parasitic nematode community, comprising Heterodera sacchari, Pratylenchus zeae, Meloidogyne incognita, Helicotylenchus dihystera, Mesocriconema tescorum and Xiphinema spp., changed with duration of the cropping cycle. The relative importance to the crop of the different species changed with time, and with development of the community structure over the course of the season. Analysis suggested that for H. sacchari, the mid-season population densities were most highly correlated with crop damage (yield loss) and therefore its damage potential for that particular season. The pest potential of other known rice pest species, such as M. incognita and P. zeae, was likely indicated earlier in the season, but the population increases of other nematode species in the community, particularly H. sacchari, compounded the interpretation of the data for other species. The use of single linear regression to assess the importance of individual nematode species conflicted with results of analyses using multiple stepwise regression, while use of cluster analysis permitted the identification of species groups at early and late stages in the cropping season.