Sorghum (Sorghum bicolor), a major crop in the USA, has a high propensity to become feral in roadsides and other habitats once escaped out of cultivated fields. Feral sorghum may threat both agricultural and natural systems directly through competition and indirectly by gee flow. Gene flow and hybridization with weedy relative such as S. halepense (johnsongrass) can further promote the weediness characters in feral sorghum. If engineered for transgenic traits, the feral sorghum can introduce novel traits into the environment. To understand the extent of ferality in sorghum, we conducted a roadside survey in south Texas comprising of Upper Gulf Coast, Coastal Bend and Rio Grande Valley regions in fall 2014. A total of 2077 sites were visited and the presence/absence of feral sorghum and johnsongrass was recorded. Seed samples were also harvested for further characterization. For each visited site, nearby land use, road type and distance to grain facilities were recorded and their relationships with the presence of feral sorghum was investigated using generalized linear models. To examine the evidence of hybridization, seeds collected from feral sorghum were grown in the greenhouse and tested for ploidy (hybrids are expected to deviate from diploidy).
Feral sorghum and johnsongrass were found in 17 and 45% of the surveyed locations, respectively. However, the two species co-occurred only at 48 (2%) sites. The probability of finding feral sorghum was lower in the presence than in the absence of johnsongrass. The presence of feral sorghum was positively related to sorghum cultivation in the nearby fields, but not to the road type. These results suggest that the persistence of feral sorghum largely depends on a continued supply of seeds. Sporadic seed spill appeared to be important along major highways, away from cultivated fields. Preliminary findings of the flow cytometry analysis showed that all plants tested were diploid. More research is currently underway to fully characterize the phenotype and genotype of different feral sorghum populations.