New Leaf Spot Disease from Fungus Found on Winterberry Trees

Mary Jones
27th January, 2024

New Leaf Spot Disease from Fungus Found on Winterberry Trees

Image Source: Natural Science News, 2024

Imagine your favorite ornamental tree, standing pretty in a garden, and now picture it having unsightly brown spots on its leaves – not exactly a vision of health, right? Well, this is what's happening to Elaeocarpus decipiens, a tree quite popular for its ornamental value in Southern China. Let's dive into what's been unraveling with these trees and how a group of scientists are playing detective to get to the root of the problem. From March 2018 to March 2021, folks at Jiangnan University noticed that about 40% of these trees on campus started to look a bit under the weather, with their leaves developing small, light brown spots. Over time, these spots grew larger, darkened to an olive brown, and ended up causing the affected parts of the leaf to die – a process known as necrosis. To figure out what was causing this leaf spot disease, scientists did what any plant detective worth their salt would do – they took samples. Specifically, they collected leaves showing symptoms from five different trees and followed a proper CSI protocol: they sterilized the leaves to make sure they were only studying the disease-causing culprit, and then they cultured what they found onto a medium made from potatoes and sugar (potato dextrose agar, to be precise) to watch it grow. What emerged was a cadre of fungi with a distinct look: olive-green with white edges and lots of "aerial hyphae" – essentially the fungal equivalent of airborne roots. Under the microscope, they observed that the fungi produced spores, which are like seeds, in a variety of shapes and sizes, organized in chains or hanging out solo. Based on these characteristics, the scientists had their prime suspect: a type of fungus known as Alternaria spp. But to nail down the ID with certainty, they used the latest in fungal crime-fighting technology. They selected three representative fungal samples and fished out their total genomic DNA, which is like the blueprint of a living organism. Then things got really high-tech as they zeroed in on three specific genes, which in fungi act kind of like a unique barcode for species identification. They amplified these genetic barcodes using primers (which are like little scouts that seek out specific genes) and ran comparisons with known sequences in databases. Lo and behold, the genes in this fungus matched almost perfectly with Alternaria alternata, a fungus known to cause leaf spots on various plants. To confirm beyond a shadow of a doubt that this fungus was the culprit, scientists conducted a lineup – they exposed healthy plant leaves to the fungus and observed if the same symptoms appeared. And indeed, they did. The inoculated leaves developed the very same olive brown spots, while control leaves (splashed with water instead of the fungus) remained healthy. A classic case of cause and effect. This isn't the first time Alternaria alternata has been accused of plant vandalism. It has a rap sheet that includes causing similar disease on sacred figs, Japanese lime trees, and other plants. However, this is the first time it's been caught attacking Elaeocarpus decipiens in China. Why's this important, you ask? Well, these trees aren't just for show. They're significant to the local economy and the environment. And with the spread of this leaf spot disease, scientists are sounding the alarm for forest conservationists: pay attention and perhaps consider how changing global climates might be contributing to the spread of plant diseases. This saga of the spotted leaves isn't just about one tree in one university campus. It's a window into the wider issue of plant health and the escalating battle between the beauty of our natural world and the microscopic organisms vying to leave their mark. It also underscores the importance of vigilance and the continuous efforts of scientists who work to keep our green companions healthy and thriving. So next time you're out enjoying the tranquility of a garden, spare a thought for the silent, ongoing work that helps keep it that green haven we all admire.

AgricultureEnvironmentPlant Science

References

Main Study

1) Occurrence of Leaf Spot on Elaeocarpus decipiens Caused by Alternaria alternata, a new disease in China.

Published 24th January, 2024

https://doi.org/10.1094/PDIS-10-23-2044-PDN


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