Heritability in the early nodulation of F₃ and F₄ soybean lines

We have previously identified differences among soybean [Glycine max (L.) Merr.] lines in early nodulation and N₂ fixation, and related early nodule development and overall plant performance under N-limited field conditions. The objectives of the present study were: 1) to estimate heritabilities for nodule fresh weight (NFW), shoot dry weight (SDW), and root dry weight (RDW) determined 17 d after inoculation (DAI); 2) to examine genetic variation for total nodule soluble protein (TSOLP) at 17 DAI, and SDW and shoot N derived from fixation (SNdfa) at the R5 growth stage; and 3) to assess relationships between early nodulation and subsequent R5 shoot mass and SNdfa. The two populations used were derived from the Minnesota-adapted cultivars Kasota and Parker, and two plant introductions PI 437966 and PI 384469B. Genetic variances within populations were significant for most traits measured at 17 DAI, and at the R5 growth stage. Heritability estimates ranged from 0.79-0.82 for NFW, 0.51-0.56 for SDW, and 0.38-0.40 for RDW, with SDW also correlated with seed size at 17 DAI (r = 0.88**). Additional correlation analyses showed SNdfa correlated with NFW (r = 0.33**) and TSOLP (r = 0.46**). The results of this study suggest that gains from selection are possible for NFW and SDW at early stages of plant development.