Discovering a New Fungus Causing Leaf Spots in Corn

Jim Crocker
16th January, 2024

Discovering a New Fungus Causing Leaf Spots in Corn

Image Source: Natural Science News, 2024

Imagine walking through a field of maize on a sunny day, only to notice that some of the plants have not been spared from the clutches of disease. Patches of yellow spots pepper the green leaves, a signal that something is amiss. This is exactly what happened in Deogaon, Uttar Pradesh, India, in February 2017. Researchers observed maize plants suffering from leaf spot symptoms that affected less than 10% of the crops in the fields. The culprit behind this condition? A fungal invader by the name of Curvularia verruculosa. Leaf spot diseases are like the unwanted guests at a garden party, and in the case of maize, they're unwelcome disturbances caused by various fungal species, including the ones you might be hearing about for the first time: Curvularia lunata, C. geniculata, and C. pallescens. However, in our story, the spotlight thief is Curvularia verruculosa. So how did the researchers make this discovery? To find out what was causing those mysterious spots to form, pieces of symptomatic tissue from 10 plants went under the microscope. Picture a tiny piece of leaf, no larger than your fingernail, diligently sterilized and prepped for its moment of scientific fame. It was placed on a nutrient-rich platform known as potato dextrose agar, jazzed up with a bit of antibiotics to keep any bacterial party crashers away, and then grown in conditions that would be the envy of any tropical vacationer: a balmy 25°C with just the right balance of sunlight and darkness. After isolating the suspect, it was time to get familiar with its characteristics. The culture was pure villainy, with dark grayish black tops and a deep brown undersurface — sure enough, it fit the description of our wanted fugitive, Curvularia verruculosa. The spores produced by this fungal outlaw were equally distinctive: shaped with gentle curves and cellular patterns that might as well have been its fingerprints. However, as any detective will tell you, looks can be deceiving, so molecular identification was brought into play to confirm the suspect's identity. DNA was extracted, specific regions were amplified, and the results were as clear as a bell: the DNA sequences matched perfectly with known sequences of Curvularia verruculosa in the global genetic database. It was an uncontestable match, the kind you see once in a blue moon: 100% identity in both the ITS region and the gene known for its involvement in cellular energy production. To ensure they had their culprit red-handed, researchers had to catch it in the act. They conducted a reenactment of the crime scene on healthy maize plants, carefully tagging each leaf with the fungus, mimicking the natural infection process. Like clockwork, in about two weeks, the same tell-tale spots appeared, the pathogen was isolated again, and its identity was confirmed for a second time. It was a full-circle moment — the equivalent of solving the whodunit in a plant's detective tale. What makes this case especially noteworthy is that, until this point, no one in India had reported Curvularia verruculosa causing such trouble on maize. Sure, it had been causing mischief on other plants like common beans and cotton in different corners of the globe, but this was its debut on the Indian maize scene. The implications of this discovery extend beyond the fields and into our understanding of plant diseases. With more knowledge about the perpetrators that lurk in the soil or cling to the leaves, farmers and scientists can devise better strategies to protect these vital crops. The work done by the sleuths of science highlights the importance of keeping a vigilant eye on the health of our planet's vegetation. After all, it's often the smallest of foes that can pose the greatest threats to our food security. Whether it's through microscopic inspection, DNA analysis, or carefully crafted reenactment scenarios, understanding and identifying plant pathogens ensures the resilience of agriculture in the face of biological challenges. And so, with this new villain unmasked, the maize fields of Deogaon can look forward to healthier days ahead, while the researchers can notch another win in the ongoing battle to keep our crops safe. Curvularia verruculosa, consider your cover blown!

AgricultureEnvironmentBiotech

References

Main Study

1) First report of leaf spot of maize caused by Curvularia verruculosa in India.

Published 13th January, 2024

https://doi.org/10.1094/PDIS-07-23-1410-PDN


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