Near‐Isogenic Lines Reveal the Role of E3 and E4 Loci in Soybean (Glycine max (L.) Merr.) Adaptation Across Latitudes in Subtropical Regions

Photoperiodic genes E1 , E2 , E3 and E4 regulate soybean adaptation by controlling flowering in response to latitude. While photoinsensitive genotypes carrying recessive alleles of these genes adapt well to higher latitudes, their role in subtropical rainfed environments remains uncertain. This study developed near‐isogenic lines (NILs, BC 3 F 4 ) with e3 and e4 recessive alleles in the genetic background of JS 97‐52 ( E3E4 )—a variety adapted to ~22° N latitude—using marker‐assisted backcrossing. The NILs were evaluated under three sowing dates at Indore (22.7° N) and across eight locations (18° N–32° N) during the summer season. Results revealed a consistent reduction in days to flowering, which was statistically significant at Palampur (32° N) and Imphal (24° N), with the greatest reduction observed in e3e4 NILs. A latitude threshold (~23° N) was identified, beyond which the photoperiodic response became more pronounced. Despite earlier flowering, the NILs maintained similar maturity duration, leading to an extended reproductive phase and ultimately higher grain yield at Palampur and Imphal. While e3 and e4 recessive alleles had no notable impact in subtropical locations, they significantly influenced flowering time, maturity duration, reproductive phase, seed weight and grain yield in sub‐temperate locations such as Imphal and Palampur.