Doctor of Philosophy (PhD)


Plant, Environmental Management and Soil Sciences

Document Type



Reasons for the gradual genetic yield improvement (21-31 kg ha-1yr-1) reported for soybean [Glycine max (L.) Merr.] during decades of cultivar development are not clearly understood. Identification of mechanisms for the yield improvement would aid in providing indirect selection criteria for streamlining cultivar development. Our objective was to identify yield components, growth parameters, phenological data, and/or other agronomic data responsible for yield improvement in 18 public southern cultivars released between 1952 and 2000. The study was done at the Ben Hur research farm near Baton Rouge, LA (300N Lat) during 2007 and 2008. Experimental design was a randomized complete block with four replications and one factor (cultivar). Data were obtained on yield, seed per area, seed size, seed per pod, pod per area, pod per reproductive node, reproductive node number per area, percent reproductive nodes, node number per area, total dry matter (TDM) at R7 and harvest index (HI). Data were analyzed sequentially at primary (seed number per area and seed size affecting yield), secondary (pod number per area and seed per pod effecting seed number per area), tertiary (pods per reproductive node and reproductive node number per area affecting pod number per area) and quaternary levels (node number per area and percent reproductive nodes affecting reproductive node number per area). Yield improvement among these cultivars was not related to length of the seed filling period, or days from emergence to R5 or R7. Neither was lodging resistance involved. Greater yield in new vs. old cultivars was mainly due to greater TDM (R7) (71%) and secondarily to higher HI (29%). Yield components responding to greater dry matter accumulation to create more yield in new vs. old cultivars were node and reproductive node number per area, pod number per area and seed number per area. A possible indirect selection criterion for yield during cultivar development is reproductive node number per area.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Board, James E.