Researchers discover new type of pathogenic fungus that infects potatoes

RUDN University biologists have discovered a new type of pathogenic fungus that infects potatoes and leads to massive crop loss. Fungi in this genus were previously known to be harmful to potatoes and other plants, but this species was considered harmless. Results published in Plant disease.

Fungi of the genus Alternaria cause a dangerous potato disease. Up to 5% of the loss of the world potato crop is due to it. Alternaria affects both grown and young plants. Leaves suffer the most, they cover with brown and light spots. Changes in photosynthesis and the fungus toxins leads to a slowdown in growth. When harvesting, tubers are also affected. A number of Alternaria species are known to cause this disease, although not all fungi in this genus are pathogenic. RUDN University biologists found that species A. alternariacida not previously seen infecting potatoes, proved to be just as dangerous.

"Potato leaf blight (early blight) is caused by Alternaria species and occurs annually in all regions of Russia where potatoes are grown. Therefore, it is important to study the biology of Alternaria and analyze their distribution. This will help us to improve the protection of potatoes from disease", said Sergey Elansky, Doctor of Biological Sciences, Professor of the Agrobiotechnological Department of RUDN University.

Affected potato leaves were collected in 2016 in Primorsky Krai in eastern Russia. The symptoms corresponded to the classical picture - dark necrotic spots with specific zoning, similar to a target, surrounded by a yellowish tissue, which indicates the action of a toxin and a violation of the formation of chlorophyll. RUDN biologists isolated spores of pathogenic fungi and transferred them to a nutrient medium for incubation. Once colonies formed, biologists were able to determine the species composition of fungal isolates.

In most cases, other species of the genus Alternaria were responsible for the disease. However, in one of the isolates, RUDN University biologists noticed that sporulation occurs in an unusual way. The conidia were smaller and more slender. Molecular and genetic analysis showed that this is a fungus of a different species - Alternaria alternariacida. This fungus is a close relative of another Alternaria (A. silybi), which has already been found in the Far East, but was first caught infecting potatoes. Biologists separately studied the pathogenicity of the new fungus. They infected healthy potato plants. As a result, the potatoes showed the same symptoms that were observed in the initially harvested leaves.

We identified most of the isolates as A. protenta. This can be done by morphological characteristics and molecular data. But sporulation in one isolate was somewhat atypical. It was a different species, A. alternariacida, which was subsequently confirmed by molecular data. As far as we know, this is the first report of a potato plant disease caused by A. alternariacida."

Lyudmila Kokaeva, PhD, Senior Researcher at RUDN University Agrobiotechnological Department