Abstract:

Summer stress characterized by high temperature and humidity is a major constraint to achieving high yield and quality in alfalfa production in the Yangtze-Huaihe region. To identify stress-adapted germplasm， a field experiment was conducted in Yangzhou from 2023 to 2024， evaluating 42 alfalfa varieties with contrasting fall dormancy （FD） ratings. We investigated a range of agronomic and physiological traits， including phenology， plant height， forage yield， leaf∶stem ratio， regrowth capacity， summer survival， and crude protein content. Grey relational analysis （GRA） was employed for an overall performance assessment. Significant varietal differences （P<0.05） were observed at regreening time， and for regrowth vigor， cumulative seasonal yield， and summer persistence. While leaf crude protein content remained stable across seasons， the leaf∶stem ratio showed considerable seasonal variation. A significant negative correlation was found between FD rating and the summer relative yield reduction rate （r=-0.50）， indicating that less dormant varieties exhibit superior heat tolerance and summer survival. GRA identified WL525HQ， Huaiyang No.4， Magnum No.801， WL656HQ， and Saidi 10 as top-performing varieties， combining high yield potential with exceptional resilience to summer adversity. This study establishes fall dormancy as a valuable proxy for selecting alfalfa varieties suitable for the Yangtze-Huaihe region， and the top-performing varieties provide a reliable genetic resource for breeding programs aimed at enhancing alfalfa productivity in this challenging environment.

Key words: alfalfa, fall dormancy rating, production performance, heat resistance, Yangtze-Huaihe region