Leaf Spot Disease on Rhododendrons Linked to Diaporthe Fungus

Greg Howard
21st January, 2024

Leaf Spot Disease on Rhododendrons Linked to Diaporthe Fungus

Image Source: Natural Science News, 2024

In southwest China, Rhododendron latoucheae, known for its lovely scent and abundant blossoms, is facing a threat that is marring its beauty. During surveys in the Baili Azalea Forest Area of Guizhou Province, researchers found that 12% of these plants suffered from a leaf spot disease that significantly diminishes their allure and economic value. Signs of the disease appeared as grey-white lesions on the leaves, bordered with a sharp blackish-brown edge and faint dark spots in the center. To study the problem, scientists collected 15 leaves that showed these symptoms. In laboratory conditions, they successfully grew spores from the leaf spots to identify and further examine the culprit, isolating three identical fungal strains. Using various cultivation methods, they meticulously observed the growth pattern and characteristics of the fungus, which included the production of two different types of spores. Morphological and genetic analysis confirmed that the fungus was Diaporthe eres—a notorious plant pathogen. The genetic proof came from amplifying and sequencing several regions of the fungus's DNA and comparing it to known data in a genetic library, which showed a high degree of similarity to previously identified strands of this species. A specialized phylogenetic analysis further cemented the identification of the isolate. To ensure that this fungus was indeed causing the disease in Rhododendron latoucheae, the researchers conducted a pot assay using a close relative of the affected plant, Rhododendron delavayi, mimicking natural conditions and successfully reproducing the disease. These steps followed a classic set of criteria known as Koch's postulates to definitively link the pathogen to the condition it's believed to cause. The same fungus was isolated once again from these artificially induced leaf spots, closing the loop in identifying the disease agent. This marks the first time that D. eres has been reported as causing leaf spot disease on R. latoucheae in China, raising concern for the ornamental plant species. With this pathogen now identified, steps can be taken towards better prevention and management strategies to protect these plants from the unsightly and harmful leaf spot disease.

EnvironmentBiochemPlant Science

References

Main Study

1) First report of Diaporthe eres causing leaf spot on Rhododendron latoucheae Franch. in China.

Published 19th January, 2024

https://doi.org/10.1094/PDIS-10-23-2271-PDN


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