Changes in photo‐thermal sensitivity of widely grown Chinese soybean cultivars due to a century of genetic improvement

Photo‐thermal sensitivity is a crucial factor that determines the phenology, adaptation and yield production of soybean. However, the change of photo‐thermal sensitivity due to a long process of soybean breeding remains unknown. To better understand this unique characteristic of soybean, we sought to evaluate the genetic improvement in photo‐thermal sensitivity of 63 widely grown soybean cultivars, spanning 83 years of breeding (1923–2006), from four main subregions in China. Days to the first flower was measured, and photo‐thermal sensitivity was calculated. We found that photo‐thermal sensitivity of cultivars in the northern Heilongjiang (NH) region showed a quadratic relationship with year of release. However, photo‐thermal sensitivity was negatively correlated with year of release in the Huang‐Huai‐Hai Valley (HH) region. There were no significant trends of change found in the mid‐southern Heilongjiang (MSH) and Jilin and Liaoning (JL) regions. The changing trend of photo‐thermal sensitivity was relatively consistent across different environments, particularly in the NH and HH regions (photoperiod, temperature or planting year). The insensitivity to photo‐thermal condition provided an advantage for modern cultivars to achieve broad adaptation.