Powdery scab is a disease of

potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Unit ...

tuber Tubers are a type of enlarged structure used as storage organs for nutrients in some plants. They are used for the plant's perennation (survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing ...

s. It is caused by the

cercozoa Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead defined by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major eu ...

n ''Spongospora subterranea'' f. sp. ''subterranea'' and is widespread in potato growing countries.

Symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showin ...

s of powdery scab include small

lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classifi ...

s in the early stages of the

disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...

, progressing to raised

pustule A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, nails, and related muscle and glands. The major function of this sy ...

s containing a powdery mass. These can eventually rupture within the tuber

periderm Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines, and shrubs. Bark refers to all the tissues outside the vascular cambium and is a nontechnical term. It overlays the wood and consist ...

.Maldonado, M. Loreto Hernandez, Richard E. Falloon, Ruth C. Butler, Anthony J. Conner, and Simon R. Bulman. "''Resistance to Spongospora Subterranea Induced in Potato by the Elicitor β-aminobutyric Acid.''" Australasian Plant Pathol. Australasian Plant Pathology 44.4 (2015): 445-53. Web. 21 Oct. 2015. The powdery pustules contain resting spores that release anisokont

zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or mo ...

s (asexual spore with two unequal length

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

) to infect the root hairs of potatoes or tomatoes. Powdery scab is a cosmetic defect on tubers, which can result in the rejection of these potatoes. Potatoes which have been infected can be peeled to remove the infected skin and the remaining inside of the potato can be cooked and eaten.Dennis A. Johnson and Thomas F. Cummings. ''Effect of Powdery Scab Root Galls on Yield of Potato.'' (2015).Plant Disease 99:10, 1396-1403

Disease cycle

In general, not a lot is known about the life cycle of ''Spongospora subterranea'' f.sp ''subterranea'' (Sss). Most of the currently-proposed life cycle is based on that of ''

Plasmodiophora brassicae ''Plasmodiophora'' is a genus in the phylum of cercozoa in the class Phytomyxea. It includes the species ''Plasmodiophora brassicae'', which causes the disease cabbage clubroot Clubroot is a common disease of cabbages, broccoli, caulifl ...

'', a closely related and better-studied

protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...

n. It has been proposed, due to this similarity, that there are two distinct stages that Sss can exist as; the asexual and sexual stages. Asexual Stage: A

infects root tissue and becomes a

uninucleate {{Short pages monitor