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Faculty Mentor

Lan Xu

Abstract

Alfalfa is the most widely produced perennial forage legume in North America. However, its use in the semiarid northern Great Plains is limited due to poor stand establishment and persistence under drought condition. The development of drought-tolerant alfalfa cultivars is of great need. Some Medicago sativa subsp. falcata populations have demonstrated promising drought resistance when compared to M. sativa. Morphological and physiological mechanisms play a critical role in drought tolerance by influencing seedling survival, stand establishment and drought recovery. Assessment of variability in physiological responses to drought among germplasm lines to drought is necessary for developing cultivars with improved drought tolerance. A greenhouse study was conducted to evaluate the variations of stomatal conductance, chlorophyll content, and root to shoot (R/S) ratio of eleven alfalfa populations under drought treatments. Eleven entries included one sativa-based commercial cultivar, six falcata-based populations, and four rangeland naturalized populations. Uniform seedlings from each population were watered to attain drought treatment regime of 100, 50, and 25% of field capacity. The 50 and 25% treatments created mild and severe drought-stress. Two falcata-based germplasms originated under annual precipitation of 250mm and 165mm natural environmental conditions demonstrated the drought tolerant associated traits. They showed either the lowest stomatal conductance or the greatest increased leaf chlorophyll content under severe drought among 11 populations. Both exhibited the highest R/S ratio under severe drought. The results indicated reducing water loss through minimizing transpiration while increasing root water absorption, and the ability of delaying leaf senescence thus retaining photosynthesis are some key traits that may contribute to drought tolerance in these falcata-based alfalfa.

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