Abstract
BackgroundAlfalfa has been cultivated in many regions around the world as an important forage crop due to its nutritive value to livestock and ability to adapt to various environments. However, the genetic basis by which plasticity of quality-relevant traits influence alfalfa adaption to different water conditions remain largely unknown.ResultsIn the present study, 198 accessions of alfalfa of the core collection for drought tolerance were evaluated for 26 forage quality traits in a field trial under an imposed deficit irrigation gradient. Regression analysis between quality traits and water stress revealed that values of fiber-related traits were negatively correlated with values of energy-related traits as water deficit increased. More than one hundred significant markers associated with forage quality under different water treatments were identified using genome-wide association studies with genotyping by sequencing. Among them, 131 markers associated with multiple traits in all the water deficit treatments. Most of the associated markers were dependent to the levels of water deficit, suggesting genetic controls for forage quality traits were dependent to the stress treatment. Twenty-four loci associated with forage quality were annotated to functional genes that may play roles in cell development or in response to water stress.ConclusionsThis study addressed the genetic base of phenotypic variation of forage quality traits under water deficit. The SNP markers identified in this study will be useful in marker-assisted selection for the genetic improvement of alfalfa with enhanced drought tolerance while maintaining forage quality.
Highlights
Alfalfa has been cultivated in many regions around the world as an important forage crop due to its nutritive value to livestock and ability to adapt to various environments
We evaluated 26 forage quality traits in a panel of 198 alfalfa accessions of the core collection for drought tolerance obtained from the USDA-ARS Western Regional Plant Introduction Station
The values of fiber-related traits, including acid detergent fiber (ADF), Neutral Detergent Fiber analyzed with amylase (aNDF), dNDF30, dNDF48 decreased as water deficit applied (Fig. 1a 1–4)
Summary
Alfalfa has been cultivated in many regions around the world as an important forage crop due to its nutritive value to livestock and ability to adapt to various environments. Alfalfa quality has been determined by many factors, including protein, fiber and lignin contents, relative feed value, total digestible nutrients, and other physical and chemical factors. The RFQ uses fiber digestibility and the total digestible nutrients of the forage to estimate intake [2]. The RFQ is an improvement over RFV as it better reflects the performance on animal fed. The RFQ emphasizes fiber digestibility while RFV uses digestible dry matter intake. Differences in the digestibility of the fiber fraction can result in a difference in animal performance when forages with a similar RFV index are fed
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