Genetics and Comparative Growth Morphology of Fasciation in Soybeans (Glycine max [L.] Merr.)

Two sets of isogenic soybean lines were used to study fasciation inheritance and to compare growth morphology between fasciated and nonfasciated genotypes. The three sources of fasciated soybean mutants have the same allele for fasciation, inherited as a single-gene recessive. No linkages were found for fasciation (f) and flower color (w), pubescence color (t), seed-coat peroxidase level (ep), or an asynaptic mutant (st2). Furthermore, f was not linked to a chromosome interchange or located on any of the three soybean primary trisomics. Grafting showed that the scion, not the rootstock, determined phenotype. There was no evidence for a diffusible, fasciation-determining substance transported up or down the stem. Fasciation could not be mimicked or delayed by external application of growth regulators. Fasciated plants had wider and heavier main stems, but total shoot dry weights at maturity were similar for fasciated and nonfasciated genotypes. Stem circumference at the middle and upper portions of the shoot and leaf number were significantly greater in fasciated than in nonfasciated plants. Seed size and total seed number per plant were similar in both genotypes, but fasciated plants had a greater percentage of one-seeded pods.