Path analyses of the yield formation process for late-planted soybean

Strategies to increase yield of late-planted soybean [Glycine max (L.) Merr.] in the southeastern USA would be improved by an understanding of how yield components interact with one another in affecting yield at both the phenotypic and genotypic levels. Our objective was to apply path analyses to data collected from previous studies to determine the relative importance of yield components in the overall yield formation process when environmental and genotypic factors were varied. Path analyses were applied within primary yield components (the predictor variables seed number and seed size, affecting the response variable yield), secondary yield components (the predictor variables pod number and seed per pod, affecting the response variable seed number), and tertiary yield components (the predictor variables pods per reproductive node, reproductive node number, percent nodes becoming reproductive, and node number, affecting the response variable pad number), Path analyses were applied to three data sets constructed from field studies conducted from 1987 to 1993 near Baton Rouge, LA (30 degrees N lat). Phenotypic analyses, which involved altered source strength (canopy assimilatory capacity as indicated by crop growth rate or light interception) during the reproductive period (R1 to R7), affected yield through adjustments in pods per reproductive node and reproductive node number. Pods per reproductive node was also the most important yield component influencing pod and seed number on the genotypic level, although negative compensation between seed number and seed size (at the genotypic level only) precluded a positive effect on yield.