Genetic Control of Long Daylength Response in Soybean

Abstract

An understanding of the genetics of the long daylength response of soybean [Glycine max (L.) Merrill] would facilitate the development of cultivars adapted to the long days of the northernmost growing areas of North America and Europe. The objective of this study was to determine the genetic control of soybean response to extension of the natural daylength to 20h using incandescent lamps. Three pairs of near‐isogenic lines (NIL) plus a long daylength insensitive check were grown outdoors and rated visually for response to incandescent long day (ILD). The same entries were further grown indoors and rated for response to extension of the natural daylength to 20h using cool white fluorescent lamps (FLD). Based on these results, entries were classified for alleles at the E3 and E4 maturity loci. Check OX619 and ILD‐insensitive NILs X2398, X2403, and X2396 were classified genotypically as e3e3 e4e4. The respective recurrent parents were all ILD‐sensitive and were classified: Evans‐e3 and Harosoy‐e3 as e3e3 E4E4 and ‘Maple Arrow’ as E3E3 e4e4. Analyses of F2 and F2:3 populations from five crosses revealed that only the e3e3 e4e4 genotype is ILD‐insensitive. Consequently, a model of two (E3 and E4), each with two alleles, each with dominance, plus epistasis of E3 on e4> is proposed to explain the ILD‐insensitivity. It was concluded that E3 is the major locus conferring long daylength insensitivity in soybean, but both E3 and E4 have to be considered when breeding for insensitivity to long daylength using ILD.