As a short-day (SD) and thermophilic plant, soybean is sensitive to photo-thermal(day length, temperature) conditions. The sensitivity of soybeans to photo-thermal response is an important domestication and adaptability trait of soybean. Under natural conditions, geographical location and/or sowing season are two important ecological factors that determine the differentiation of wild and cultivated soybeans, and they work together to regulate the growth and development of soybeans through environmental factors such as day length and temperature. Therefore, the study of the geographical and seasonal differentiation of photo-thermal comprehensive response characteristics during growth periods of soybeans may help soybean introduction and breeding for adaption.

A total of 1 519 representative world wild and cultivated soybeans were selected and tested with two-year spring seeding and summer seeding field trials at Dangtu, Anhui Province. The difference in growth period between sowing seasons was used to evaluate the photo-thermal comprehensive response sensitivity (PTCRS) of each soybean accession, and to study the photo-temperature response characteristics of the growth and development stages of various geographic and ecological soybeans.

(1) The photothermal response characteristics of soybeans existed throughout the period of growth and development. (2) With the migration of wild soybeans from south to north, the PTCRS of the days from sowing to flowering (DSF) and days from sowing to maturity (DSM) decreased, the PTCRS of the days from flowering to maturity (DFM) increased, and the photothermal response type changed from the front-sensitive and post-insensitive to the front-insensitive and post-sensitive, and the photothermal response of DSM is sensitive. (3) With the domestication of wild soybeans to cultivated soybeans, the PTCRS of DSF and DSM decreased by 20% and 16%, respectively, and relatively small changes were observed for the PTCRS of DFM. The main photothermal response type changed from the front-sensitivity and post-insensitive to the front-insensitive and post-sensitive and the front-insensitive and post-insensitive. (4) The PTCRS of DSM of summer-autumn (SA) and spring (SP) sowing type soybeans both show gradual decrease from south to north. The geographical differentiation of PTCRS of DSF and DFM of SA and SP is different that when migrate from south to north, the PTCRS of DSF of SA decreased, and the PTCRS of DFM of SA first increased and then decreased, and the PTCRS of DSF of SP there was no significant change, and the PTCRS of DFM of SP decreased. (5) With the Huang-Huai and Yangtze River Valleys and South China as the origin center of cultivated soybeans, the PTCRS of DSF, DFM and DSM decreased significantly when spreading north to Northeast China, Russian Far East and Southern Sweden. The PTCRS of DSF and DSM decreased when spreading east to Korean Peninsula and Japan Island and west to Northern North America, Southern North America and the Central and South America, but no obvious change was observed for the PTCRS of DFM. When cultivated soybeans spread south to Southeast Asia, South Asia and Africa, the PTCRS of DSF and DSM increased, and there was no significant change in PTCRS of DFM. (6) Comparing the PTCRS between different ecotypes in the same eco-region, the PTCRS of DSF, DFM and DSM of SP was the smallest, and the PTCRS of DSF of wild soybeans was stronger than that of SA, and the PTCRS of DFM of wild soybeans was weaker than that of SA, and there was no significant difference between the PTCRS of DSM of wild soybeans and SA. Comparison of PTCRS between different geographic and sowing-seasonal eco-type of soybeans, PTCRS of DSF: Southern wild soybeans is the most sensitive, followed by wild soybeans in the Yangtze River Valleys and SA in the Southern, followed by Huang-Huai wild soybeans and SA in the Yangtze River Valleys, and the remaining geo-ecotypes have no significant differences, all of which are relatively insensitive; PTCRS of DFM: SA in the Yangtze River Valleys is the most sensitive, followed by the Northeast and Huang-Huai wild soybeans and the Southern and Huang-Huai SA, and the remaining geo-ecotypes have relatively small differences, all of which are relatively insensitive; PTCRS of DSM: there is no significant difference between wild soybeans and SA in the Southern and the Yangtze River Valleys, all of which are sensitive, followed by Huang-Huai wild soybeans, followed by Northeast wild soybeans and Huang-Huai SA, and the PTCRS of SP is the smallest, and it decreases significantly with the increase of latitude.

The photo-thermal comprehensive conditions determined by geography and sowing season are important factors affecting soybean growth and development. Differentiation of response to photo-thermal comprehensive conditions existed in wild and cultivated soybeans of different geography and sowing season ecological types. With cultivated soybeans spread from Huang-Huai and Changjiang River Valleys and South China to geographical regions of different latitudes in the world, different changes were observed for the photo-thermal comprehensive response during growth period. Sensitivity to photo-thermal during sowing to maturity is the original trait of soybean, and the summer-autumn sowing type soybeans in the Middle and Lower Yangtze Valleys may be the most cultivated type with this wild primitive trait.