Agronomic Performance of Selected Soybean Morphological Variants in Irrigation Culture with Two Row Spacings

Soybean [Glycine max (L.) Merrill] plant morphology can be altered with the use of qualitative genes. These alterations may be useful in deriving high yielding cultivars, particularly in irrigated and/or narrow row cultural environments. Near-isogenic lines of the soybean cultivars ‘Clark’ and ‘Harosoy,’ which possessed alleles (singly or in combination) conditioning determine (dt₁) or semideterminate (Dt₂) stem growth, shortened (S) or lengthened (sᵗ) stem internode length, narrow (ln) or oval (lo) leaflet shape, five (Lf₁) or seven (lf₂) leaflet numbers, wavy leaflet margins (lw₁), dense (Pd), sparse (Ps), semi-sparse (Ps⁶), or appressed (pa₁pa₂) pubescence, or earlier flowering and maturity (e₂), were evaluated for agronomic performance in 18- and 71-cm row spacings under irrigation for 2 years. The Clark-Dt₂S, -Dt₂Lf₁ln, -pa₁pa₂, and -Dt₂ isolines were significantly greater in yield than Clark, while Clark-Lf₁, -lf₂, -dt₁, -S, -dt₁S, and -dt₁sᵗ were significantly lower in yield. The Harosoy-Pd isoline was significantly greater in yield than Harosoy, while Harosoy-pa₁pa₂, -dt₁S, and -dt₁ were significantly lower in yield. The interaction of isoline ✕ row spacing was not significant in the combined 2-year data. There were significant effects of the various alleles on maturity, plant height, lodging, seed quality, and seed weight. Only the Dt₂ allele consistently increased yields, but other alleles (e.g., Pd, pa₁pa₂) increased yields depending upon the cultivar in which these were present. Significant inter-allelic and allele ✕ genetic background interactions were observed in some cases indicating that allelic ‘worth’ may depend on complementarity with other genes. The alleles Dt₂, Pd, pa₁pa₂, and Dt₂S appear to have some potential for yield improvement in soybeans, depending somewhat upon the genetic background in which these are introduced, and warrant consideration by soybean breeders in cultivar development or population improvement.