Validation of the Principal Axis Model (PAM) and its Application to Genotype Selection in Field Pea (Pisum sativumL.) Crops

The principal axis model (PAM) uses a principal axis and an ellipse to characterize the variation in the relationship between the seed (SWT) and plant (PWT) weights of individual plants within a crop. The theoretical linkage between the magnitude and variability of plant harvest index (PHI), and therefore seed yield per unit area, and changes in the components of the PAM was examined using data from four field pea (Pisum sativumL.) genotypes sown at 9, 49, 100, 225 and 400 plants m-2. A strong linear relationship (R2>93.8%) between SWT and PWT and a negative SWT-axis intercept were confirmed for all crops. Analyses indicated that decreased variability of PHI within a crop would result from selection to: (a) increase the SWT-axis intercept of the PAM; (b) increase the slope of the PAM; (c) optimize the ellipse location; and (d) minimize the deviation around the principal axis. The first three methods were used to explain yield differences (P