Discovering a New Fungus Behind Leaf Damage in Fragrant Mint Plants

Mary Jones
2nd February, 2024

Discovering a New Fungus Behind Leaf Damage in Fragrant Mint Plants

Image Source: Natural Science News, 2024

Imagine this: a plant with superpowers, used for centuries in traditional Chinese medicine suddenly falls ill. That's right, even plants get the sniffles—or in this case, leaf blight. This is the tale of the annual medicinal plant, Elsholtzia ciliata, belonging to the mint family, that's been flexing its healing muscles across China. So, picture a leaf. It starts off looking all green and happy, but then out of the blue, it's hit with this weird, creeping necrosis (fancy word for 'death of tissue') starting at the tip. Slowly, the blight takes over, like a shadow swallowing light, until the whole leaf is a goner. Not the most pleasant tale so far, right? But it gets interesting. Scientists in the field noticed that a good chunk of E. ciliata was waving a white flag—15% of them were showing symptoms of this leaf blight. That's about 30 out of 200 plants surveyed at a medicinal plant base in Daying county of Sichuan Province. And those science folks? They didn't just stand there; they put on their detective hats and got to work. Now, before we dive into the microscopic nitty-gritty of their investigation, let's talk about methods. They took samples from leaves, both sick and healthy parts, and gave them the whole spa treatment—ethanol, sodium hypochlorite, and a triple rinse with sterile water—to kill any meddlesome microbes on the surface. These samples were then placed on potato dextrose agar (I promise, it's not for fries) and left in the dark at a cozy 25°C. Fast forward seven days, and something's growing. It's a fungus, and not the truffle kind. Initially, it put on a little white show, then jazzed it up with grayish-green conidia (those are spore-producing structures) with white fringes. These spores? Dark brown, smooth as jazz, and pear-shaped, all set up in a pretty unique pattern. By now, you're probably thinking, "Get to the point, buddy!" Well, this fungi turned out to resemble a known troublemaker—Alternaria alternata. To throw more science at it—and because they didn't trust looks alone—our researchers sequenced bits of its DNA. They uploaded this genetic material to GenBank (kind of like a Facebook for microorganism profiles), where they matched it to a troublemaking fungus type called CBS 595.93—the abracadabra to confirm that we indeed have A. alternata on our hands. Now, let's talk about an experiment that sounds like something out of a sci-fi movie. They made a spore suspension, which is basically like a smoothie of spores and water, and misted it onto some unsuspecting non-sick E. ciliata plants under cover. After giving the plants a little darkness and warmth, the disease popped up again. Can you believe it? The control plants, sprayed with just water, remained blight-free and smug. So, they fulfilled Koch's postulates—essentially, the plant world's version of finding the culprit beyond a doubt. They proved that A. alternata was the one throwing the blight party on E. ciliata. And here's the kicker: this is the very first recorded instance of this fungus bullying E. ciliata in China. That's kind of a big deal. Why does this matter to you and me, you ask? Well, this E. ciliata plant isn't just any old shrub. It's a crucial component of traditional Chinese medicine, which means this leaf blight isn't just a plant problem; it's an economic challenge, too. If this situation doesn't get the needed spotlight and smarts thrown at it, folks relying on this plant for medicine might find their cure-all in short supply. So, let's tip our hats to the brainy bunch unraveling this mystery. Even as we speak, they're probably out there, peering into microscopes and petri dishes, making sure that the medicinal mint's future looks healthier and greener.

AgricultureEnvironmentPlant Science

References

Main Study

1) First Report of Alternaria alternata Causing Leaf Blight on Elsholtzia ciliata in China.

Published 1st February, 2024

https://doi.org/10.1094/PDIS-09-23-1814-PDN


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