| A soybean population was developed by Dr. Graef and denominated UP2 Protein. This population was developed by mating 7 unadapted high-protein plant introductions. Three cycles of recurrent selection were conducted. The 7 parents of the base population (Cycle 0), and the 10 parents of each successive cycle (Cycle 1, Cycle 2 and Cycle 3), were tested in a randomized complete block design with three replications in 7 different environments representing two years (2001 and 2002), two locations (Mead and Lincoln, NE) and two water conditions (irrigated and rain-fed). Results demonstrated the effectiveness of recurrent selection to increase seed protein content from 451.1 g kg-1 in Cycle 0 to 492 g kg-1 in Cycle 3. The average gain of 14.3 +/- 0.7 g kg-1 cycle-1 for seed protein content is the highest published when gain is averaged over more than one cycle. A concomitant significant (p < 0.01) decrease of 7.0 +/- 0.5 g kg-1 cycle-1 in seed oil content was observed over three cycles. Mean seed yield decrease but not significantly, from 2110 kg ha-1 in Cycle 0 parents to 1948 kg ha-1 in Cycle 3 parents. When other agronomic traits were analyzed, significant (p < 0.05) changes were observed for flowering date, reproductive period, lodging and plant height. The shortening in the reproductive period resulted in a difference of 5.8 days between parents of Cycle 0 and parents of Cycle 3. Besides seed oil, other seed traits were analyzed. Seed weight decreased significantly (p < 0.01) from 16.1 cg seed -1 for Cycle 0 parents to 14.2 cg seed-1 for parents of Cycle 3. Seed density showed no significant changes over cycles of selection. Fatty acids composition of the oil, showed no significant differences among cycles for palmitic, oleic, linoleic, and linolenic acid. Only sterearic acid showed significant differences (p < 0.01) among cycles. |
