Variability for Seed Size and Yield in Two Tall Dropseed Populations

Tall dropseed [Sporobolus asper (Michx.) Kunth var. asper] is a drought-tolerant, perennial, warm-season grass that has potential for forage and soil conservation purposes. A prairie and an adjacent roadside population from northeastern South Dakota were evaluated for seed yield and size characteristics for 3 years (1985-1987) in a space-plant nursery at Brookings, S. Dak. The objective was to obtain information on between and within population variability and intraplant variability that would provide a basis for designing a breeding program to improve seed production and quality in this germplasm. The roadside population produced significantly (P<0.01) higher seed yields and larger mean 100-seed weight than the prairie population. Percent small seed (based on screen-separation of seed yields of individual plants into small, medium, and large seed size classes) decreased significantly (P<0.01) as seed yield increased, but the volume of small seed increased concurrently with seed yield. Percent large seed increased significantly (P<0.01) with increased seed yield and mean seed size. Highly significant (P<0.01) differences were found among years for seed yield and mean seed size, but all plants produced seeds of each size class each year. Inter- and intrapopulation genetic variability was indicated for yield of the large seed size class. Screen-separation of individual plant seed yields could be used to identify superior genotypes to be used in the development of a cultivrr that produces a high percentage of large seed.