Natural outcrossing of sorghum and sudangrass in the central great plains

Amount of natural outcrossing in a species is one of the primary determining factors in selection of breeding methods. Existing literature on natural outcrossing of sorghum is dated and limited in geographical reference. Experiments were designed to investigate natural outcrossing in contemporary sorghum, Sorghum bicolor (L.) Moench, B- and R-lines, and in sudangrass, Sorghum bicolor (L.) Moench. Four R-lines and four B-lines were seeded in rows in isolation at Mead, NE, and allowed to intercross in each of 2 yr. Bulked seed from each row was planted and proportion of offtypes recorded. Outcrossing ranged from 0.1 to 13% in R-lines, and from 0.5 to 9% in B-lines. Outcrossing among sudangrass plants with white or green midribs transplanted in isolation in each of 2 yr was estimated by utilizing the dominant gene for white midrib as a marker. Panicles from green midrib plants were tagged to indicate approximate date of pollination. At maturity, the panicles were divided into top, middle, and bottom thirds and threshed. Seed from each panicle section was planted and proportion of white midrib plants recorded. Outcrossing ranged from 0 to near 100% on individual sudangrass plants and was highly variable. Harvest of panicles pollinated during the middle of the pollination period should maximize outcrossing in sudangrass, but the use of nuclear male-sterility genes is still recommended for improvement of sudangrass through recurrent selection. For sorghum breeding procedures requiring a high degree of self-pollination, selfing under pollination bags is recommended.