Estimation of alfalfa fall dormancy using spaced plant and sward trials across multiple environments

Background:Alfalfa is a globally important forage crop.Cultivars are characterized by fall dormancy(FD).FD affects biomass yield and winter survival and is used to identify appropriate growing regions of cultivars.It has historically been assessed by measuring the natural height of regrowth in autumn of spaced plants in the field.Because commercial alfalfa is normally grown as a solid planted sward,FD could be different if plants were grown under real production conditions.The objective of this experiment was to assess whether FD ratings obtained from swards were similar to those obtained on spaced plants.Methods:We evaluated 20 alfalfa cultivars in field trials established in 2015 at five locations in the United States.We harvested the trials in early autumn and measured regrowth plant height approximately 3 weeks later in 2015 and 2016.Results:Autumn plant height responded as expected for the established check cultivars in all locations.Fall dormancy ratings for cultivars under both management systems were highly correlated.Conclusions:Estimating FD from spaced plant height measurements in autumn is very robust,and using height data from sward plots gives equivalent results to that measured in spaced plant nurseries.This finding has many practical advantages.

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.