CHAMPAIGN, Ill. – Esther Ngumbi, assistant professor of entomology at the University of Illinois at Urbana-Champaign, became interested in farming as a young girl in Kenya. She asked her father for a piece of land so that she could try growing her own plants, and he gave her land alongside a river.

“I planted my cabbages alongside the river, and they really were a source of joy. I remember just going and sitting somewhere on top of the hill to look at the vibrant green,” she said. “They were doing so well until the rain came. By the time the flooding waters had receded, all my cabbages were gone, and the joy I had derived every morning just from these cabbages was cut short.”

This childhood memory stuck with Ngumbi, and she thought a lot about how she could have rescued her plants. Later, when she moved to Illinois, she saw the same thing happen again as the state experienced massive and historic flooding in 2019. The 2019 Midwestern Floods affected nearly 14 million people in Midwestern and Southern states. Researchers estimate that the agricultural sector faced losses exceeding $6 billion, with at least 1 million acres of farmland in nine major grain-producing states having flooded.

“(The flooding) shocked me as I read newspapers and saw that the farmers, the growers, they didn’t know what to do. Nobody knew what to do. Looking in the scientific literature, I saw that there were no answers to what flooding does, what farmers could have done, or what farmers were going to do (after the flooding),” Ngumbi said. “There were no answers at all. That solidified my quest to understand flooding.”

Due to climate change, floods are becoming more frequent and intense. Just recently, Hurricane Helene caused catastrophic flooding, stretching from Florida to southern Appalachia. Sometimes, the impacts of flooding on crops are very observable and obvious. For example, standing water deprives plants of oxygen, halting their core physiological processes. This can leave plants withered and yellowed, and prolonged water exposure will eventually kill plants as their root systems decay. Plants that survive flooding will have difficulty absorbing nutrients through their damaged root system, and weakened plants will become magnets for insects and pathogens.

Ngumbi uses tomato plants to study the less observable impacts of flooding, like how plants communicate through chemicals. Plants release volatile organic compounds (VOCs), chemicals that help them communicate with other organisms in the environment. VOCs play a role in many different functions, like attracting pollinators, repelling herbivores, and communicating distress.

In a study investigating two different types of heirloom tomato varieties, Cherokee Purple and Striped German, Ngumbi and her team found that the tomato plants differed in gene expression and the VOCs they emitted before and after flooding and herbivory. After the tomatoes experienced flooding and herbivory by beet armyworm, they increased their VOC emissions. Primarily, the plants released more terpenoids, organic chemicals that help to improve plant fitness by attracting predators of insect herbivores and decreasing ongoing oxidative stress. The study results show that some plants have adaptations to aid in recovering from flooding and insect damage.

“We see a few varieties (of tomato) that do show some strength or adaption against flooding. They develop appetitious roots, and we see higher levels of antioxidant substances,” Ngumbi said. “But in the long term, once flooding has happened, it’s just a downward spiral with tomatoes. You will never recover your yield.”

Ngumbi has also studied corn, comparing cultivated maize with wild teosinte, the ancestor of modern corn. Like tomatoes, the research showed that cultivated corn and wild teosinte released different VOCs after flooding and herbivory stress. Results suggest that teosinte was more tolerant than maize due to metabolic changes that helped the plant cope with the stressors.

In the future, Ngumbi plans to investigate other varieties of tomatoes to understand their natural abilities to defend themselves against flooding. She is interested in understanding if the plants have lost these traits through breeding and if it’s possible to find genetic components that can be transferred to improve tolerance.

“We want to make sure that we are not just breeding for (tolerance to) drought, elevated temperatures, and insects,” she said. “A lot of plant varieties today have not been bred for flooding, so we think breeding (for tolerance to flooding) will be one of the solutions.”

Beyond breeding and improving plants genetically against flooding, Ngumbi added that another potential solution is the application of rescue nitrogen. Some corn farmers apply nitrogen after flooding, which aids in maintaining yield, although it isn’t wholly effective at recovering flooded plants. Other solutions to be investigated include cover cropping in a way that helps plants resist flooding and finding foliar applications that could help plants boost their defense against pathogens.

“My hope is that we start being proactive and not waiting for when (floods) happen,” she said. “This is going to be a world we experience more often, and we need to have these varieties and solutions so that when it happens, farmers do not have to lose their yield for something that science could have been prepared for.”