Soybean Growth and Agronomic Performance in Response to the Long‐Juvenile Trait

Abstract

A long‐juvenile (LJ) trait that delays flowering has been incorporated into temperate soybean [Glycine max (L.) Merr.] genotypes for adaptation to short‐day conditions. Growth and agronomic effects of the LJ trait as influenced by maturity group are not well documented. A study was undertaken in which five LJ near‐isoline pairs in Maturity Groups IV, V, and VI were evaluated at early (late April), normal (late May), and late (late June) sowing dates near Pendleton, SC (34° N lat) in 1993 and 1994. Growth stages, plant morphology, and agronomic characteristics were determined. Extended periods of vegetative growth in response to the LJ trait resulted in one to three additional V‐stages and increased branch growth during the vegetative period. The LJ trait lengthened the period between flowering and pod set (R1 to R5) 38, 17, and 11% at early, normal, and late sowings, respectively, in Maturity Group IV isolines and shortened it 18 and 12% at early and normal sowings for Maturity Group VI isolines. The period of seed fill (R5 to RT) was unaffected by the LJ trait. The LJ trait influenced reproductive morphology and plant seed yield distribution with responses being affected by maturity group. Seed yield in response to the trait increased 43 and 16% at early and normal sowings in Maturity Group IV isolines and 22% at early sowings in the Maturity Group V isoline. Seed quality of LJ genotypes in Maturity Group IV isoline pairs was improved 49 and 35% at early and normal sowings. Our results indicate that maturity group influences growth and agronomic responses related to the LJ trait and that early maturing genotypes are more suited for its introgression to maximize potential benefits of the trait.