U.S. alfalfa variety trials confirm breeding progress for yield and broad adaptability of commercial varieties, but widespread genotype-by-trial variation

Authors: Tilhou, Neal; Riday, Heathcliffe

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2025
Publication Date: 9/23/2025
Citation: Tilhou, N.W., Riday, H. 2025. U.S. alfalfa variety trials confirm breeding progress for yield and broad adaptability of commercial varieties, but widespread genotype-by-trial variation. Crop Science. https://doi.org/10.1002/csc2.70157.
DOI: https://doi.org/10.1002/csc2.70157

Interpretive Summary: Alfalfa is an important crop in the United States. Farmers selecting among different cultivars of alfalfa rely on trials managed by public institutions such as universities. This study combined data from decades of variety trials of alfalfa. Overall, our research indicates that farmers should select varieties only after they have been tested in at least four different trials. We also found that U.S. plant breeding is significantly improving performance of alfalfa since biomass yield of new alfalfa varieties increase by 0.6% per year.

Technical Abstract: Public forage variety trials are the only objective source of information for alfalfa producers purchasing seed. There has been extensive research on improving the efficiency of individual trials, but limited research guiding the best practices of sharing information within a network of trials. A retrospective analysis of hundreds of alfalfa (Medicago sativa L.) trials in the greater northeastern United States revealed that individual trial results have limited precision within a broader set of trials. Based on mean variety yield in a trial, only 36.2% of genetic variance was consistent across many trials. Genotype-by-environment effects explained 26.2% of the variance. Residual variance was confounded with genotype-by-trial variance and explained 37.6%. This resulted in standard errors of 4.1%, 3.3%, and 2.9% (mean variety deviation from trial yield) for varieties evaluated in two, three, and four trials, respectively. Practically, four or five trials are suggested as minimum threshold for a reliable yield estimate in alfalfa. Fortunately, the scale of genotype-by-environment variation is relatively small relative to other crops, suggesting that superior alfalfa varieties are superior across a large geographic range. Last, there was breeding progress for biomass yield (+0.63% per year; standard error=0.029%; p=9.0x10-78) in alfalfa between 1988-2017.