Characteristics of Endogenous Hormone Variations in the Roots of Alfalfa (Medicago sativa L.) Cultivars of Different Fall Dormancies During Spring Regrowth Stage

Regrowth traits of alfalfa (Medicago sativa L.) in spring are closely related to its fall dormancy before winter. In order to determine the relationship between fall dormancy (FD) grade and hormone variation pattern and provide academic references for the variety improvement and production of alfalfa, the variations of gibberellins (GA₃), indole-3-acetic acid (IAA), and abscisic acid (ABA) in alfalfa roots during regrowth period in spring were examined by high performance liquid chromatography (HPLC). The study involved seven alfalfa cultivars that belonged to four fall dormant grades, i.e., 2, 4, 6, and 8. The results showed that the differences in spring regrowth among the alfalfa cultivars were partially associated with their root hormone levels. The alfalfa cultivars that belonged to the same dormancy grades presented similar variation trends in endogenous hormone content in their roots during the spring regrowth stage. At the early regrowth stage, cultivars with a higher dormant grade had a higher GA₃ concent and a lower ABA content in their roots than the cultivars with a lower dormant grade; and IAA content in roots of non- and semi-fall dormancy cultivars was higher than that of fall dormancy cultivars. During the whole period of spring regrowth, the root ABA content of fall dormancy alfalfa cultivar is significantly higher than those of semi- and non-fall dormancy cultivars. GA₃ contents in the roots of all cultivars under study showed a double-peak dynamic curve; root IAA contents of the studied cultivars presented a downward trend. But the trend did not significantly differed among the different fall dormant cultivars. The higher GA₃ content and lower ABA content in root of non-fall dormancy alfalfa lead to its earlier regrowth. Regrowth time and rate of alfalfa can be regulated by exogenous GA₃ or ABA at the early regrowth stage to meet producing requirement.