Wheat Protein Concentration after Two Cycles of Divergent Selection for Seed Density

Improvement of seed protein concentrations in wheat ( Triticum aestivum L.) has been hindered by lack of effective selection methods applicable to early‐generation segregating populations. The objective of this study was to evaluate selection for imbibed seed density as a method to increase or decrease seed protein concentrations of bulk winter wheat populations. Twelve populations, each in F 3 , F 4 , F 5 , and F 6 generations derived from crossing exotic and adapted cultivars (each cross possessing at least one high‐pl~protein parent), were used in two cycles of selection without recombination. Low‐ and high seed density fractions were selected visually after low‐temperature seed imhibition using sucrose‐NaCl solutions with densities of ⊄ 1.24 and 1.25 Mg m −3 , respectively. Six of the 12 Cycle 1 selected populations had significant protein increases with low seed‐density selection, and four populations were reduced in seed protein concentration with high density selection. Protein changes achieved, using a selection intensity of ⊄ I0%, ranged from 2 to 4 g kg −1 for density selected vs. unselected populations. After two cycles of selection, protein concentrations were significantly increased in 9 of 12 low density selected populations, ranging from 3 to 7 g kg −1 . High‐density selection was less effective, with significant protein decreases in 6 of 12 populations, ranging from 3 to 5 g kg −1 less than unselected bulks. Selflng within populations did not influence selection efficiency. Change in kernel weights of selected bulks was small. A negative association between protein concentration and grain yield was noted. Lack of relationship between initial protein differences after separation and results in field trials suggests that non genetic variation in protein concentrations of individual seed may limit effectiveness of the technique.