Evaluation of Cold Resistance in Alfalfa Varieties Based on Root Traits and Winter Survival in Horqin Sandy Land

The Horqin Sandy Land in China is a key alfalfa production base, challenged by low winter temperatures and large diurnal temperature shifts, affecting alfalfa's winter survival. Alfalfa roots are the primary organs responsible for winter adaptability; consequently, by investigating the changes in the root physiology and nutritional components of alfalfa during the overwintering period, we can enhance our understanding of its mechanisms for cold resistance. Over the course of two years (2022-2023), field trials were conducted on 40 alfalfa varieties selected from both domestic and international sources for their potential cold resistance. This study assessed winter survival rates and analyzed root contents, including soluble sugars, starch, soluble proteins, and the concentrations of carbon (C), nitrogen (N), phosphorus (P) and their stoichiometric ratios. Principal component analysis, subordinate function analysis, and cluster analysis were employed for comprehensive evaluation. Biochemical markers varied significantly across varieties. The C, N, and starch contents in the roots were the main factors determining cold resistance. The varieties were categorized into four groups: Category I included five highly resistant varieties ('Baimu 202', 'WL168HQ', 'Zhongmu No. 1', 'Gongnong No. 1', and 'Legacy'); Category II consisted of six moderately resistant varieties; Category III included twenty-eight slightly resistant varieties; and Category IV contained one non-resistant variety ('3010'). This study recommends the adoption of the five varieties in Category I to enhance alfalfa cultivation in the Horqin region. This research provides valuable theoretical and practical guidance for improving the cultivation of alfalfa in the cold regions of northeastern China, supporting the development of the local livestock industry.