INTERPRETING UPLAND RICE YIELD AND PRATYLENCHUS-ZEAE RELATIONSHIPS - CORRESPONDENCE ANALYSES

Correspondence analyses were used to explore the relationships between yield and populations of Pratylenchus zeae in an upland rice field an d in a greenhouse experiment. Initial soil (Pi) and final root (Pf) po pulation 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 hi gh Pf. Low Y was linked to medium or high Pi and medium Pf. Medium to very high Y were clustered with undetectable Pi and very low or high P f. All yield levels were independent of very high Pi. In the greenhous e experiment where seven nematode inoculum levels and three fertilizer levels were evaluated, low Y was associated with medium or high Pf an d high Y with high or low Pf. The analyses indicated that nematode-yie ld interaction involved a complex, dynamic process, in which the root- carrying capacity probably was a determining factor. Correspondence an alysis, which does not require assumptions on the shape of nematode po pulation-yield relationships or on variable distributions, revealed me aningful associations in these complex data sets.