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Cross-fertilization in Seed Production in Relation to Forage Yield of Alfalfa¹

Experiments were conducted to determine the relationship between percentage of cross-fertilization in alfalfa, Medicago sativa L, seed production, and forage yield, and to determine the competitive relationships between plants of hybrid and nonhybrid origin at three seeding rates. The percentages of cross-fertilization in seed production were measured by classifying the flower color of progeny from white- and yellow-flowered markers that were planted with blue- and purple-flowered materials. Seed lots that varied from 30 to 91% of hybrid origin were seeded in replicated field plots to study yield and other traits, and to provide plants that were dug and classified for flower color.

Percentage of cross-fertilization in seed production was not significantly correlated with forage yield of alfalfa in any of three experiments. The percentages of plants of hybrid origin that became established in the field by the fall of the seeding year, from a spring seeding, were highly correlated with percentages of cross-fertilization in seed production in two experiments, with r values of 0.758 to 0.924, significant at the 1% level. In the fall of the first harvest year, the average percentages of plants of hybrid origin were 81, 87, and 90% in plots seeded at 4.5, 9.0, and 13.4 kg/ha, respectively. These percentages exceeded the average percentage of cross-fertilization in seed production by 29 to 38%. In the fall of the second harvest year, the average percentages of plants of hybrid origin were 95 and 96% in plots seeded at 9.0 and 13.4 kg/ha, respectively.

The percentages of plants of hybrid origin were significantly different for, and increased with, seeding rate by the fall of the year of seeding in one experiment and by the fall of the first harvest year in another experiment.

Key Words: Crossing percentage • Hybrid alfalfa • Competition • Seeding rates • Medicago sativa L.

² Research agronomist, ARS, USDA, and professor of agronomy, Univ. of Nebraska, Lincoln, NE 68503.

Received for publication June 13, 1975.