Date of this Version
Cultivated sorghum (Sorghum bicolor subsp. bicolor) can interbreed with its close weedy relative shattercane (S. bicolor subsp. drummondii). The introduction of traits from cultivated sorghum into a shattercane population could contribute to the invasiveness of the wild shattercane population. An in situ experiment was conducted across two years to determine the potential for pollen-mediated gene flow from grain sorghum to shattercane. Shattercane with juicy midrib (dd) was planted in a soybean field in concentric arcs at varying distances from a sorghum pollen source with dry midrib (DD). The arcs were placed so that prevailing winds would carry pollen from the sorghum to shattercane. Shattercane panicles in anthesis during sorghum pollen shed were tagged and seeds were collected from those shattercane panicles. Progeny were evaluated using the dry midrib marker to determine outcrossing rate. Outcrossing was greatest for shattercane placed within the source and differed between years (3.6±0.76% in 2008 and 16.1±1.31% in 2009). Outcrossing rate generally declined as distance increased for both years. In both years outcrossing was seen (0.09±0.04% in 2008 and 0.34 ±0.07% in 2009) at the farthest distance evaluated (200 m). Wind direction and speed was also a determining factor as wind run (wind speed*proportion of wind in that direction) affected outcrossing rate for all pollination periods. Results indicate that genes from cultivated sorghum and any associated traits will likely be introduced into shattercane populations at distances of at least 200 m and that outcrossing rate is dependent on weather factors such as wind, and possibly pollen source strength.
Adviser: John J. Lindquist