Interpreting Upland Rice Yield and Prafylenchus zeae Relationships: Correspondence Analyses'

Correspondence analyses were used to explore the relationships between yield and populations of Pratjlenchus zeae in an upland rice field and in a greenhouse experiment. Initial soil (Pi) and final root (Po population densities of P . zeae, and yield (Y) of rice CV. UPL Ri5 were determined at 490 spots in the field. Very low Y was linked to very high Pf. Low Y was linked to medium or high Pi aiid mediilni Pf. Medium LO very high Y were clustered with undetectable Pi and very low or high Pf. All yield levels were independent of very higli Pi. III the greenhouse experiment where seven nematode inoculuni levels and three fertilizer levels were evaluated, low Y was associated with medium or high Pf and high Y with high or low Pf. The analyses indicated that nematode-yield interaction involved a complex, dynamic process, in which the root-carrying capacity probably was a determining factor. Correspondence analysis, which does not require assumptions on the shape of nematode population-yield relationships or on variable distributions, revealed meaningful associations in these complex data sets.