College of Agriculture & Natural Resources
Plant Science & Landscape Architecture

Dr. Alyssa Koehler

“Bridging research and extension to manage disease in stevia and field crops”

Title: Bridging research and extension to manage disease in stevia and field crops

On September 27th, Dr. Alyssa Koehler visited UMD invited by the Plant Science and Landscape Architecture Department as a speaker for the Fall ’18 Seminar Series. The title of her talk was “Bridging research and extension to manage disease in stevia and field crops” and focused on her journey as a PhD student and the challenges she faced with her project, which involved the introduction and establishment of a new crop: Stevia, in North Carolina, a state where tobacco, has been traditionally the key product.

The seminar started introducing stevia, an herbaceous perennial plant native to Paraguay that belongs to the Asteraceae family, the same family that hosts sunflowers, daisies and chrysanthemums. The particularity of this plant and what makes it so valuable is that its leaves contain multiple diterpene glycosides that extracted (and processed in a liquid, powder, tablet or granulated form) can be used as a natural, non-caloric sweetener. It is said that stevia leaf extracts are approximately 300 times sweeter than sugar but do not raise blood glucose levels.

This characteristic is the reason why so many low-calorie products feature stevia, and this trend doesn’t seem to go away anytime soon auguring a market that will continue growing strong. To meet the increasing demand there has been a cumulative interest in establishing stevia as a crop in the USA. So far, North Carolina at the hands of Dr. Koehler and company, has been leading the production viability evaluation due to its favorable climate, especially the high levels of natural rainfall, and non-less important, the existing infrastructure.

In 2011, some small “exploratory plantations” started and the acreage dedicated to this crop continues expanding slowly ever since as the interest on this plant sparks farmers looking for new opportunities in a world where the tobacco industry, although still profitable, is being discouraged and losing field. Therefore, stevia represents a chance to diversify operations, rotate crops or start a new business, among others.

But introducing a new crop means that you must face several challenges, first and foremost: diseases. Dr. Koehler and her team were the first to report several pathogens affecting stevia in North Carolina, some of them probably seen in other parts of the world but not documented in the literature. Among the diseases encountered during the evaluation process they found Pythium Root Rot caused by Pythium myriotyum, P. irregulare and P. aphanidermatum, Stem Rot caused by Sclerotinia sclerotium, Charcoal Rot caused by Macrophomina phaseolina and Stem and Root Rot caused by Sclerotium rolfsii.

As new diseases continued to emerge she had to focus her research in developing disease management strategies to control them considering not only the efficacy of the products, that ranged from several types of fungicides to biocontrol agents, but when to apply them and how often, keeping in mind that the production cost couldn’t go too high if they wanted to keep it lucrative. So, the approach had to be not only effective but also economically feasible. What products to choose was also an issue because currently there are no fungicides or biological controls officially labeled for Stevia in the country.

A very interesting fact is that when performing these studies, they noticed that in addition to keeping plants disease free during season, some fungicides (QoI specifically) seemed to enhance plants’ health and vigor as they entered the overwintering period, a major concern they had since successful overwintering into the second- and third- year crops is critical to long-term profitability and ultimate establishment.

Dr. Koehler then, turned her focus in trying to understand the mechanisms by which this behavior was occurring, they studied two possibilities or scenarios, whether the chemicals were causing beneficial physiological changes to the plants or were affecting the soil microbiome in a positive manner, their results shade a light onto the second option.

As her talk was moving towards the end, she mentioned her new horizons, what new challenges she might be facing in her new position as an Extension Plant Pathologist at the University of Delaware and how unforeseen events during her PhD turned out to be some of the most interesting and fascinating challenges she has dealt with. Dr. Koehler presentation was definitely refreshing, full of charisma and provided grad students the opportunity to listen to someone fresh off the interview process on how to move to the workplace after grad school. We wish them good luck.

By: Humberto Castillo González (Dr. Koehler Seminar on Sep. 27th).






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