We studied accessions of Medicago sativa L., M. varia Mart., and M. falcata L. in 2019–2023 in the Central Black Earth Region (Belgorod oblast) on typical chernozem soils. The study aimed to determine the association between crude protein content in alfalfa phytomass and other economically valuable traits to identify superior accessions in long-term trials that are promising for breeding focused on feed value. The experiment included cultivars and breeding lines of diverse geographic origin evaluated in stands of the first, second, and fifth years of use. Protein content in forage mass proved to be a stable breeding trait, determined by genetic characteristics of the accessions by 81.4% and by stand age by 15.5%. Protein content showed strong positive correlations with dry matter yield per cut and with total yield over two cuts (r = 0.757–0.782, p = 0.05). We found no correlation with seed yield (r = 0.042, p > 0.05). Quartile grouping of accessions by protein content identified groups with distinct trait expression: low (Q1), 177.6–192.3 g/kg; medium (Q2), 192.6–203.6 g/kg; increased (Q3), 204.4–224.5 g/kg; and high (Q4), 225.8–235.9 g/kg. On average over the study period, accessions in Q1 and Q2 significantly underperformed those in Q3 and Q4 by 16.0–35.8% in dry matter yield per cut and in total over two cuts, by 6.7–23.7% in plant height, and by 5.4–12.8% in leafiness. For further breeding to enhance feed value and increase protein content, accessions in Q4 are recommended, including Krasnoyaruzhskaya 2, Belgorodskaya 7, Alekseevskaya 1, SI-138, M-195, SI-139, and PO-155 m (M. varia, blue-hybrid sortotype), as well as Salsa, Kreno, Planet, Plato, Luzelle, and Galaxy (M. sativa). Accessions from Q3, including Gloria and PO-169 mk, also merit use.
Sajfutdinova et al. (Mon,) studied this question.