Use of Morphological, Developmental, and Plant Nitrogen Traits in a Selection Scheme in Soybean

A 3-yr study was conducted to determine the response in seed yield from a tandem selection scheme in which the first step was to select desirable lines from each of two single-cross populations of soybean [Glycine max (L.) Mew.] for morphological and developmental traits, by using independent culling. The second step was to select for greater plant N content at the R5 developmental stage. The genetic material was 213 F₆-derived indeterminate lines from three maturity groups (79 lines early, 93 medium, and 41 late) from a single-cross population (IX139) and 102 lines from three different stem-termination types (28 determinate lines, 40 semideterminate, and 34 indeterminate) from different cross (IX149). Yield increase from the first part of the selection scheme was 2.2% in the early, 1.8% in the medium, and 5.5% in the late maturity groups of IX139, with a mean of 3.2%. Selection for morphological and developmental traits decreased seed yield by 4.4% in the determinate group of IX149 and increased the seed yield in the semideterminate and indeterminate groups of IX149 by 1.0 and 4.7%, respectively. In the second portion of the tandem selection scheme, selection for greater plant N content at R5 decreased seed yield by an average of 0.06% across the maturity groups of IX139 and increased the yield by an average of 1.1% across the three stem-termination types of IX149. The average yield increase across the groups, locations, and years was 0.5%. In assessing the overall response to tandem selection in all groups within IX139 and IX149, most groups responded positively, but the determinates decreased in seed yield by 3.8%. Plant N content at the R5 stage, because of its poor association with seed yield and the inconsistent seed-yield response to selection, did not seem to play a significant role in determining the final yield of F₆-derived lines of soybean. Journal Paper no. J-14926 of the Iowa Agric. and Home Econ. Exp. Stn. Project no. 2764. Research partly supported by the Iowa Soybean Promotion Board.