Divergent mass selection for seed density in winter wheat: Concomitance with seed protein concentration and kernel hardness

The maintenance and improvement of the nutritional value, and end-use processing quality of any crop will benefit producer and consumer alike. Divergent mass selection for high- and low-imbibed seed density has been utilized for the indirect selection of seed protein concentration in winter wheat (Triticum aestivum, L.). The efficacy of this selection method for seed protein concentration, and its concomitant effects upon kernel hardness, weight per kernel and grain yield was the principle objective of this study. The relationship between seed protein concentration and kernel hardness, per se, was also of interest. Twelve segregating bulk winter wheat populations were derived from crosses, each including one or more high protein parents. Heterogeneity within the parental stock also existed for textural kernel hardness. Seed of the bulk populations was separated into high- and low-density fractionations based upon the differential constitutive seed-protein:starch density gradient established via seed imbibition with water. Unselected bulk populations, and populations selected for divergent seed density were field evaluated at Lincoln, NE in 1985 and 1986, and Vernon, TX in 1986. Kernel hardness was determined using an individual Kernel Hardness Tester developed by the USDA-Agricultural Research Service/Instrument Research Laboratory for the Federal Grain Inspection Service. Divergent mass selection for imbibed seed density resulted in changes in seed protein concentration, kernel hardness, weight per kernel, and grain yield. Changes associated with selection for low-density imbibed seed included increased seed protein concentration (+2g kg$\sp{-1}$), increased weight per kernel (+0.2 mg kernel$\sp{-1}$), and decreased grain yield ($-347$ kg ha$\sp{-1}$). High-density selection was reflected by decreases for kernel hardness ($-0.9$ kernel hardness index units), weight per kernel ($-0.3$ mg kernel$\sp{-1}$), and grain yield ($-276$ kg ha$\sp{-1}$). Utilization of densimetric flotation for seed protein concentration amelioration appeared most effective in populations that were less heterogeneous for textural kernel hardness. A phenotypic correlation of r = $-0.20$ (P $\u3c$ 0.01) was calculated between seed protein concentration and kernel hardness for seed from nurseries grown at Lincoln (1985), and Vernon (1986)