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. [ABSTRACT FROM AUTHOR]