determining the relationship between population density of white tip nematode and rice yield

the relationship between initial population density of rice white tip nematode (aphelenchoides besseyi) and yield was examined on oryzae sativa cv. alikazemi. experiments were conducted in greenhouse, micro-plot and field conditions. seinhorst’s model was used to describe the relationship between nematode population density and crop yield. the parameters of the model, minimum yield (m), constant coefficient (z) and tolerance limit (t) were obtained from the experimental data. on this basis, the predicted yield was calculated within the initial population (pi) range. to evaluate the difference between the observed yield (yo) and the predicted yield (yp), a discrepancy ratio (dr) was calculated. the results revealed that there was a significant correlation between mean yield reduction and nematode populations (p