Agronomic Performance of Selected Soybean Morphological Variants in Irrigation Culture with Two Row Spacings1

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Abstract
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.