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Document Type

Dissertation - University Access Only

Award Date


Degree Name

Master of Science (MS)


Biology and Microbiology

First Advisor

Yajun Wu


Alfalfa (Medicago sativa L.) is a major forage legume, grown extensively worldwide, with important agronomic and environmental attributes and high economic value. Abiotic stress presents a major challenge for alfalfa production, and developing alfalfa cultivars with improved stress tolerance is the key to sustain its high production. Identification of alfalfa germplasm with superior stress tolerance and understanding the mechanisms that contribute to their stress tolerance is critical for a successful breeding effort. To identify alfalfa with greater drought or freezing tolerance, I examined different germplasms for their survival or growth performance under stress conditions. I included some naturalized alfalfa germplasms collected from the Grand River National Grassland in South Dakota, where annual precipitation is about 16 inches and summer drought occurs periodically and frigid temperatures and severe winter are normal. The hypothesis is that the naturalized alfalfa may have developed freezing and drought tolerance mechanisms, which enable them to survive and thrive in the harsh environments. The greenhouse screening experiments identified two germplasms with better freezing survival at young vegetative stages and one germplasm with distinctively higher water use efficiency under drought compared to other alfalfa germplasm tested. The results

xiii from physiological and molecular analysis of the freezing tolerant germplasms revealed that these two germplasms differed in cold response; suggesting different mechanisms may contribute to their freezing tolerance. To understand the mechanisms in salinity tolerance in alfalfa, I conducted physiological analyses of two salt-tolerant germplasms that were recently selected from a greenhouse breeding/screening effort by our collaborators. The genotype that showed the most consistent performance in salinity survival tests, showed improved stem/leaf growth and biomass production. The salinity tolerant genotype accumulated more soluble sugars and showed more effective stomatal closure under salinity stress, which may have contributed to its ability to prevent tissue from dehydration. The results also suggested that the salt tolerant genotype have greater capability of dealing with oxidative stress induced by salinity and greater capability of minimizing salt accumulation in root cells and xylem. My research supports the hypothesis that there is high potential to improve abiotic stress tolerance in alfalfa despite the complexity of stress tolerance traits. The genotypes identified and characterized in this study can be useful resources for developing cultivars with improved stress tolerance. This study established the foundation for studying abiotic stress tolerance mechanisms and for identifying molecular markers or genes that are important for stress tolerance in alfalfa.

Library of Congress Subject Headings

Alfalfa--Effect of stress on
Alfalfa--Drought tolerance
Alfalfa--Effect of salt on
Alfalfa--Frost resistance


Includes bibliographical references (pages 181-186)



Number of Pages



South Dakota State University


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