In a paper published Sept. 8 in the journal Communications Biology, scientists from Washington University in St. Louis and the University of Arkansas report that a crop pest called weedy rice has become widely herbicide resistant in regions where herbicide-resistant rice is planted. The study highlights challenges facing U.S. rice farmers when they battle a weedy enemy that is closely related to a desirable crop plant.
The genetic investigation was conducted with samples gathered in rice fields in Arkansas, where almost 50% of the nation's rice is grown.
Weedy rice is a closely related cousin of crop rice. It aggressively competes with cultivated rice in the field, leading to loss of yield and reductions in harvest quality that compromise market value. Weedy rice infestations cause an estimated $45 million in economic losses in the United States each year and hundreds of millions of dollars worldwide.
Biologists used whole-genome sequences of 48 contemporary weedy rice plants to show how herbicide resistance evolved by gene flow from crop rice. Almost all other cases of herbicide resistance in agricultural weeds result from selection of tolerant genotypes in the weed species. Just 20 years after herbicide-resistant rice was first adopted in the southern United States, the majority of fields with a history of herbicide-resistant rice cultivation have weedy rice plants that are also herbicide resistant.
"Throughout its nearly 200-year history in the United States...