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How to Stop a Crop Invader:

Dr. Sarah Yakimowski investigates herbicide resistance and sexuality in an invasive species

August, 2017

by Natalia Mukhina

Dr. Sarah Yakimowski

Banting Post-Doctoral Fellow Dr. Sarah Yakimowski, Queen's Biology

What Sarah Yakimowski explores could be easily transformed into a sci-fi blockbuster or Stephen King bestseller. Just imagine: an aggressive crop weed, native to Mexico and southwest North America, is rapidly spreading north toward Michigan and Minnesota. The next destination is Ontario, where it will soon invade, devouring the yield of cotton, soybean and corn. There are no weapons to defeat it; chemical weed killers no longer have any effect. What is this creepy invader?

“It is called Amaranthus palmeri (A. palmeri), and it is a really problematic crop weed,” says Yakimowski, one of the 2017 Banting Postdoctoral Fellowship winners. This prestigious award provides financial support to young researchers who will contribute to Canada’s reputation as a country with high standards for science. Funded by the Natural Sciences and Engineering Research Council for two years, Yakimowski will focus on how to better inform strategies for controlling the spread of A. palmeri.

The thing Yakimowski particularly loves about her research is that it enables her to employ both her interest in population genetics and background in plant reproductive biology. That makes her very well equipped to dive into such a multifaceted project that is framed by a set of challenging questions.

“Why has this plant extended its range so rapidly and aggressively? How does it evolve resistance to the herbicide? Those questions are of great importance for me because they touch on both theory and practice, fundamentals of evolutional biology and applied agricultural problems,” explains Yakimowski.

Sarah Yakimowski using a laptop computer.

Going further, one question scientists do not yet have an answer to is whether herbicide resistance has evolved once or several times and then spread geographically, or herbicide resistance is evolving independently, popping up in a range of geographic locations. Another gap in knowledge concerns the role of reproductive traits in maintaining such resistance.

Strikingly, A. palmeri exhibits separate sexes, female and male. “It is very uncommon for the weedy species to have that sex strategy,” underlines Yakimowski. Colonization in weeds is typically associated with hermaphroditism.  It allows plants to fertilise themselves through self-pollination and provides what scientists call ‘reproductive assurance’. A. palmeri, on the contrary, has separate sexes and depends on wind to carry pollen from male to female plants. More unusually, it turns out that A. palmeri females can putatively produce seeds asexually, e.g. without fertilization from pollen.

Yakimowski calls this reproductive model a ‘best of both worlds strategy’, because A. palmeri “is not just using sexual reproduction or clonal reproduction. It has the option to employ both strategies.” 

There is a hypothesis that A. palmeri populations mix up their genes through sexual reproduction and thereby produce a variety of gene combinations including those responsible for herbicide resistance. Then, those combinations replicate by asexual reproduction. “At large, I am trying to understand whether combining sexual and asexual strategies of reproduction influences rapid geographic spread and the evolution of herbicide resistance,” explains Yakimowski.

How should strategies to minimize A. palmeri reproductive success and prevent northward movement be developed and implemented? On the flip side, it is not only a weed but historically also an important edible crop. Its leaves and seeds were consumed by several Native American tribes, and presently some of Amaranth species are used as subsistence crops in Sub-Saharan Africa. Could we not kill them with herbicides, but rather just control them?

“It is my motivating interest in this project,” replies Yakimowski with enthusiasm. “I am wondering whether understanding the genetic basis of the reproductive biology can inform some novel strategies for managing the spread of this species and decreasing its reproductive potential in a natural way”.

Yakimowski’s professional journey to her current research has led her virtually everywhere in Canada. Born in Saskatchewan, she did both an undergrad and a master’s degree at Queen’s, then a PhD at the University of Toronto, and a postdoc at the University of British Columbia, but eventually returned to Queen’s. When speaking about the differences between those places, she highlights that Queen’s Biology Department encourages students to raise their research competencies from their first days at the university, which is incredibly valuable training for them.

“The undergrads become integrated into the labs from the very beginning, and the students are expected to do high quality work while learning. I have not seen a program like that at any other institution”. Obviously, it creates a unique research culture, and Yakimowski believes undergrads and grads working together add valuable insights to research at the department.

Yakimowski stresses that the depth and scope of her current study demand a complex integrative approach and a combination of field, lab and greenhouse research methods. While the Banting fellowship is two years in length, Yakimowski believes the project has a longer-term trajectory. As an adjunct teaching professor, she also sees in the project a variety of possibilities for students who have interests in both ecology and genetics.

“My dream now consists of setting up my own lab to have students contributing to the research. There are a lot of unanswered questions that we need to address at a larger geographic scale. I am open to students who want to become involved with research in conjunction with my program.”

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