Genetic control of photoperiod response in early-maturing, near-isogenic soybean lines

Photoperiod response is one factor responsible for the regional adaptation of soybean [Glycine max (L.) Merr.] cultivars. Few photoperiod response studies have been carried out with lines containing alleles for late maturity at only one or a few loci. An understanding of the photoperiod response of early-maturing soybean lines would facilitate cultivar development in short-season areas. The objectives of this study were to investigate the photoperiod response of early-maturing 'Harosoy' near-isogenic lines with indeterminate and determinate growth habit and to examine the genetic model for sensitivity to natural day length extended to 20 h with incandescent lamps [incandescent long day length (ILD)]. Harosoy near-isogenic lines were grown in the field under natural day length and no. The same lines were also grown in growth cabinets under 12- and 20-h photoperiods with cool white fluorescent plus incandescent lamps. Under natural day length, E(3) and E(4) alleles each delayed flowering 5 d and maturity 15 d while the E(1) allele delayed both flowering and maturity approximate to 16 d compared with the alternative early-maturing alleles. The E(3) and E(4) alleles each delayed flowering 30 d under no compared with natural day length. The E(1) allele did not delay flowering or maturity under ILD compared with natural day length. Under 12-h days in a growth cabinet, there were no differences among near-isogenic lines for flowering or maturity, but the loci responded differently in the 20-h photoperiods. The E(3) allele exhibited the largest photoperiod response, delaying flowering 24 d and maturity 84 d, compared with 12-h photoperiods. These photoperiod-sensitivity loci produced differential photoperiod responses that may be useful for short-season cultivar development.