Location: Wheat, Sorghum and Forage ResearchTitle: Rate of shattercane x sorghum hybridization in situ Author
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2013
Publication Date: 7/1/2013
Publication URL: http://handle.nal.usda.gov/10113/57090
Citation: Schmidt, J.J., Pedersen, J.F., Bernards, M.L., Lindquist, J.L. 2013. Rate of shattercane x sorghum hybridization in situ. Crop Science. 53:1677-1685. Interpretive Summary: One way that plant breeders can make sorghum more profitable for farmers is to incorporate genes for herbicide, insect, and disease resistance so that fewer expensive pesticides are required to grow it. However, sorghum can pollinate the noxious weed shattercane, resulting in hybrid progeny that have those resistance genes. There is some concern that over time, shattercane populations may gain enough resistance genes through repeated hybridization with sorghum that the weed will become even more difficult for farmers to control. Researchers at the USDA-ARS in Lincoln and the University of Nebraska-Lincoln conducted a study to estimate the rate at which hybridization may occur. Results showed that the average rate was 3.6 to 16 percent when sorghum and shattercane plants grew immediately next to each other (as would occur in a sorghum field where shattercane was a weed), decreasing to 2.6 percent when shattercane grew 200 m away (as would occur if shattercane were growing in a ditch or field adjacent to a sorghum field). Thus, traits in sorghum are expected to pass into shattercane at relatively low levels where the two species grow in close proximity.
Technical Abstract: Cultivated sorghum [Sorghum bicolor (L.) Moench subsp. bicolor] can interbreed with a feral weedy relative shattercane [S. bicolor nothosubsp. drummondii (Steud.) de Wet ex Davidse]. Traits introduced from cultivated sorghum could contribute to the invasiveness of a shattercane population. An experiment was conducted to determine the potential for pollen-mediated gene flow from grain sorghum to shattercane. Shattercane with juicy midrib (dd) was planted in soybean [Glycine max (L.) Merr.] fields during 2 yr in concentric arcs at varying distances from a 0.39 ha sorghum pollen source with dry midrib (DD). The arcs were placed so that prevailing winds would carry sorghum pollen to the shattercane. Seven hundred twenty seeds from each of over 300 shattercane panicles in anthesis during sorghum pollen shed each year were collected. Progeny were evaluated by phenotype to determine rate of hybridization. Hybridization averaged 3.6% within the source in 2008 and 16.0% in 2009 and declined as distance increased. Hybridization as high as 2.6% for an individual panicle was measured at the farthest distance evaluated (200 m). Wind direction and speed were also measured and their product affected hybridization rate for all pollination periods. Results indicate that genes from cultivated sorghum will likely be introduced into shattercane populations at distances of at least 200 m and that rate of hybridization is dependent on weather factors such as wind. Source size is also important in determining hybridization rate but was not studied here.