Adjustment of the Soybean Phenology Using the E₄ Locus

Delays in reproductive development of soybean [ Glycine max (L.) Merr.l segregants grown under the long daylengths of higher latitudes have impaired the use of elite germplasm from lower latitudes when developing cultivars for short‐season areas. The responses of soybean to long daylength are under the control of at least two loci, but only E 3 has been shown to affect the phenology of plants grown in the field. The objectives of this study were to measure the effect of E 4 on the phenology of Maturity Group (MG) 00‐I soybeans grown in the field and under incandescent long daylength (ILD) created by extending the natural daylength to 20 h using incandescent lamps, and to identify the growth stage at which selection for ILD‐insensitivity is appropriate. Most ILD‐insensitive plants were able to mature before frost under ILD and selection conducted at or close to R5 under ILD permits identification of ILD‐insensitive genotypes. Growth stage measurements recorded on three different F 2 populations (homozygous for e 3 ) grown in the field indicated dominance of E 4 over e 4 . Alleles of E 4 influenced the duration of pre‐and post‐flowering periods on ‘Evans’ and ‘Harosoy’ backgrounds, whereas it only affected post‐flowering period in ‘Maple Amber’ background. The E 4 locus had a stronger delaying effect in later maturing backgrounds, indicating a potential nonadditive interaction between E 4 and other unknown maturity loci. It was concluded that selecting e 3 e 3 e 4 e 4 segregants in a population arising from a late by early maturity cross should help to limit the number of backcrosses to early elite lines required to recover acceptable maturity. This may allow more genes from the late parent to be retained by the early segregants, thereby broadening the gene poll available in a given maturity group.