Manifestation of Breeding Traits and Properties of Forage Productivity in Groups of Alfalfa Varieties with Different Resistance to Viral and Phytoplasma Infections

The studies aimed at the breeding evaluation of alfalfa varieties with different resistance to alfalfa witches’ broom (AWB) were conducted in 2019–2023 in the Belgorod oblast. A total of 52 breeding samples belonging to the Medicago sativa L., M. varia Mart., and M. falcata L., were studied. The soil was typical chernozem with a humus content (according to Tyurin) of 4.7–5.0%. Sowing was carried out in 2019, and counts were made in 2019–2023. The Belgorodskaya 86 variety sown every five numbers was the standard. The seeding rate was 100 viable seeds per one linear meter. The group of cultivar samples (n = 10) with low resistance to AWB (with prevalence variation of 24.3–34.9%) is characterized by greater protein accumulation (by 44.6 g/kg, t = 8.0, p < 0.05) and higher foliage (by 4.8%, t = 3.7, p < 0.05) and height (by 25.3 cm, t = 6.2, p < 0.05) compared to the group of cultivar samples (n = 12) resistant to AWB (prevalence variation of 4.6–9.1%). Samples with high resistance to AWB belong to the yellow and yellow hybrid alfalfa varieties (Pavlovskaya 7, PO-172, Marusinskaya 425, PO-173, Sarga, PO-174, Victoriya, 20-89 N, 193-95d, PO-175, SGPR-8, and Vela × Sarga), are characterized by increased longevity, and form a stable hay yield for 5 years of the life of the grass stands. Samples with low resistance to AWB belong to the blue and partially blue hybrid alfalfa varieties (Krasnoyaruzhskaya 2, SI-139, SI-138, Plato, Verko, Luzelle, Salsa, Kreno, Galaxy, and Planet). In the first 3 years of life of grass stands, they are distinguished by a higher productivity of forage mass, which then sharply decreases.