Variability and Breeding Behavior in Big Bluestem Populations from Eastern South Dakota

Three spaced-plant big bluestem (Andropogon gerardii Vit.) nurseries at Brookings, South Dakota were analyzed for their genetic variability and agronomic potential. Unselected native collections, the 1972 nursery, was comprised of 34 strains each representing a site collection from the eastern edge of South Dakota. The first cycle recurrent selection nursery, established in 1977, was comprised of progeny of 19 plants from the 1972 nursery that were exceptional seed producers in the drought year 1976. The second cycle recurrent selection nursery, established in 1976, was comprised of progeny of 33 agronomically desirable plants from open-pollinated nurseries established from difference southeastern South Dakota collections. These collections were from selected plants in relict colonies in southeastern South Dakota. The objectives of this study were to describe the variation in the populations studied, to estimate heritabilities of the agronomically desirable characteristic and to determine the most efficient breeding methods to produce a superior variety. Higher significant differences for seed yield, vigor, leafiness and plant height were found among strains in the 1972 nursery and among half-sib families in the 1976 and 1977 nurseries. Highly significant differences for seed weight were found among families in the 1976 and 1977 nurseries. Broad sense heritability estimates for strains were high plant height, heading date and pollination date in the 1972 nursery. Narrow sense heritability estimates based on one year’s data were extremely high for seed weight, plant height, vigor, leafiness, number of flowering culms and seed yield in the 1977 nursery. Positive assortative mating (like to like) must have been responsible for inflationary effects on the heritability estimates. Narrow sense heritability estimates based on two years’ data were moderately high for vigor, leafiness and plant height in the 1976 nursery. Estimates based on one year’s data were moderately high for seed yield and fertility index and very high for seed weight. Phenotypic and genetic correlations between agronomic characters in the 1976 and 1977 nurseries were generally positive, indicating that simultaneous multitrait selection for forage and seed characters would be profitable. Multiple regression and path coefficient analysis of seed yield components in the 1977 nursery indicated that number of flowering culms, size and/or number of racemes per culm and fertility index all contributed directly to seed yield. Number of flowering was the most important while size and/or number of racemes per culm and fertility index were both considerably more important than seed weight in determining seed yield. A composite made from open-pollinated seed of plants with heavy seeds (means 100 seed weight = .26g) from the 1976 nursery produced significantly taller seedlings than a composite comprised of plants selected for forage and seed yield (mean 100 seed weight = .20g) from the same nursery. A seed weight is highly heritable, mass selection for heavy seed should enhance seedling vigor. Mass selection should be extremely effective for seed weight and plant height and moderately effective for seed yield, vigor, leafiness, fertility index and number of flowering culms. More precision in selection, however, for these characters would be possible based on progeny test data. No sizable negative genetic correlations between characters were observed, consequently simultaneous multitrait selection should be effective