Managing glyphosate-resistant weeds is a challenge for growers in the north-central United States. Weeds typically become resistant to herbicide(s) when the same herbicide is used repeatedly for several years in the same field or due to mutation.

• Once herbicide-resistant weeds evolve, they can be spread by pollen and/or seed movement, known as pollen- and seed-mediated gene flow, respectively.
• Gene flow via vegetative propagule has rarely been addressed, but could be an important avenue for certain weed species.
• Reproductive biology differs markedly among weed species, as does the potential for gene flow.
• Pollen-mediated gene flow at a distance could allow the spread of rare herbicide-resistant alleles and favor the evolution of multiple herbicide-resistant biotypes through the accumulation of different resistant genes in an individual weed or weed population.
• The speaker will discuss examples of common waterhemp, Palmer amaranth, and giant ragweed to demonstrate the role of gene flow in transfer of herbicide-resistant alleles. For more information about speaker’s research program see https://agronomy.unl.edu/jhala.

Important Reading

• Pollen-mediated gene flow from glyphosate-resistant common waterhemp (Amaranthus rudis Sauer): consequences for dispersal of resistance genes. Nature Scientific Reports 7:44913. 
• Modeling pollen-mediated gene flow from glyphosate-resistant to -susceptible giant ragweed (Ambrosia trifida L.) under field conditions. Nature Scientific Reports 7:17067.
• Interspecific and intraspecific transfer of metabolism‐based mesotrione resistance in dioecious weedy Amaranthus. The Plant Journal.