I can barely hear Esther Ngambi over the roar of the greenhouse fans as she shows me round her rooftop laboratory in Muriel Hall. The benches are filled with tomato plants, and the tomatoes don't look good. Half of the plants are submerged in water boxes. Their leaves are turning yellow and wilting. Some of the dead tomatoes have flowered. I saw a baby tomato or two on a few leathery plants.
This is just not the one torture on tomatoes. Someone has tied small bags to their trunks. Inside the baggage, plump green caterpillars are munching on tomato leaves.
Entomology professor Ngombi has questions — a number of them — and so she sets out to reply a few of them. She's deliberately flooding tomatoes to see how they could reply to flooded farmers' fields — a scenario that's becoming more common in consequence of climate change.
“In nature, there are many stresses on plants during flooding,” Ngombi says. “Once tomatoes are flooded, they're already vulnerable, so it's likely that they're attracting insects, which like to feed on vulnerable plants. We investigated this. are how plants cope with the combined stress of flooding and herbivory.”
This explains the caterpillars. They are the larval type of the tobacco hornworm. They are feeding on one in all the 2 heirloom tomato varieties that Ngumbi is using within the experiment: Cherokee Purple and Striped German.
Half of the tomato plants within the greenhouse will not be flooded, allowing the team to check stressed plants with plants grown under more normal conditions. But further investigations are underway here.
“Also, within this experiment, we're looking at microbes,” says Ngumbi. “We want to understand how the microbial community changes under flooded conditions.”
One of Ngumbi's important focuses is how soil microbes affect plant health and productivity. She is fascinated by mycorrhizal fungi, which form a detailed relationship with plant roots, offering plants essential elements similar to nitrogen in exchange for root-supplied glucose.
All of the tomato plants are growing in soil from an Illinois farm, but half of the plants were also inoculated with mulch from a neighborhood farmer who has developed his own recipe for growing mycorrhizal fungi within the soil. Ngombi desires to see if the vaccine makes a difference within the plants' ability to defend themselves against the caterpillars.
To measure plant defenses, Ngumbi's team collects samples of gases emitted by plants and screens them for volatile organic compounds, the chemicals plants use to repel these pests. who eat them.
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Two years later, Ngumbi publishes the outcomes of those and other laboratory experiments. He found that the 2 tomato varieties differed in gene expression and the volatile compounds they released — before any intervention. And when flooded, the 2 tomato varieties have very different chemical release profiles than when grown under normal conditions. Herbicides affected the production of those volatile compounds, but not as much as flooding did.
Today, the experiments proceed, and Ngumbi's interest in the results of flooding has only intensified. In a recent review published within the journal, she describes most of the changes that occur when plants are submerged in water for days or perhaps weeks at a time.
“Flooding differs from other climate-related stresses because it deprives plants of oxygen, a necessary and indispensable element and substrate for plant growth and development,” writes Ngumbi. Flooding disrupts plant metabolism and energy production. It interferes with photosynthesis. Flooding kills useful bacteria and promotes pathogenic microbes within the soil. It may compromise the power of plants to defend themselves against diseases and harmful insects similar to tobacco hornworm.
Ngombe also warned that increased flooding could undermine a long time of research aimed toward making plants more resilient to climate change. Flooding can thwart efforts to construct soil quality and microbial health to make crops more resilient to stresses similar to heat and drought. Flooding may wipe out the advantages of genetic engineering or plant breeding.
With the severity and frequency of floods predicted to extend by about 7% for each 1°C rise in global average temperature, Ngumbi writes, scientists must consider the impact of floods to “build climate resilient crops.” Monumental advantages might be protected.”
Ngumbi is affiliated with the Carl R. Woese Institute for Genomic Biology at U. of I.