Helminthosporium solani

Silver scurf is a plant disease that is caused by the plant pathogenHelminthosporium solani. Silver scurf is a blemish disease, meaning the effect it has on tubers is mostly cosmetic and affects “fresh market, processing and seed tuber potatoes.”[1] There are some reports of it affecting development, meaning growth and tuber yield.[2] This is caused by light brown lesions, which in turn change the permeability of tuber skin and then it causes tuber shrinkage and water loss, which finally causes weight loss.[1] The disease has become economically important because silver scurf affected potatoes for processing and direct consumption have been rejected by the industry.[1] The disease cycle can be divided into two stages: field and storage. It is mainly a seed borne disease and the primary source of inoculum is mainly infected potato seed tubers. Symptoms develop and worsen in storage because the conditions are conducive to sporulation. The ideal conditions for the spread of this disease are high temperatures and high humidity. There are also many cultural practices that favor spread and development. Luckily, there are multiple ways to help control the disease.

Species of fungus
Silver scurf blemishes on a tuber

Helminthosporium solani
A tuber with silver scurf blemishes.
Scientific classification
H. solani
Binomial name
Helminthosporium solani

Durieu & Mont., (1849)

Brachysporium solani
Dematium atrovirens
Helminthosporium atrovirens
Spondylocladium atrovirens

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Silver scurf blemishes on a tuber

Silver scurf is a plant disease of potato, which is caused by the anamorphicascomycete fungus, Helminthosporium solani. Potato tubers are the only known host of Helminthosporium solani. It is a highly specific pathogen which does not have a secondary host or alternate host. A common symptom of this disease is blemishing on the surface of the potato tubers. These blemishes are tan and/or gray due to a loss of pigment, and they are usually irregularly shaped. Also, a post-harvest symptom can be shrinkage and shriveling of the outer tissue of the potato due to water loss.[3] Black spots can also be found on the surface of infected tubers, which are a sign of the disease. These are made up of conidia and conidiophores of the pathogenic fungus.[4] The conidia are characterized by being very darkly melanized and having multiple pseudosepta. Another characteristic of this fungus is the absence of motile spores.

Like with many other fungal plant diseases, a diagnosis can be made by looking for the specific sexual structures of the fungus and observing them for the specific characteristics of silver scurf.[4] Another way that silver scurf can be diagnosed is through molecular techniques, such as PCR and sequencing to identify the presence of the pathogen. The primer pair, HSF19-HSR447, has been generated to be specific for amplifying only a section of Helminthosporium solani DNA.[5]

Currently, no known host factors have been identified that have been linked to increase susceptibility or development of the disease. It seems as though the environmental conditions are what plays a major role in severity of the disease.

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