Powdery scab

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Powdery scab
Sporosori.jpg
Sporosori (survival structure) of the powdery scab pathogen
Scientific classification
(unranked):
SAR
(unranked):
Rhizaria
Phylum:
Cercozoa
Class:
Phytomyxea
Order:
Plasmodiophorida
Family:
Plasmodiophoraceae
Genus:
Spongospora
Species:
Spongospora subterranea
Trinomial name
Spongospora subterranea f. sp. subterranea

Powdery scab is a disease of potato tubers. [1] It is caused by the cercozoan Spongospora subterranea f. sp. subterranea and is widespread in potato growing countries. [2] [3] Symptoms of powdery scab include small lesions in the early stages of the disease, progressing to raised pustules containing a powdery mass. These can eventually rupture within the tuber periderm. [4] The powdery pustules contain resting spores that release anisokont zoospores (asexual spore with two unequal length flagella) to infect the root hairs of potatoes or tomatoes. [5] 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. [6]

Contents

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 , a closely related and better-studied protozoan. 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 zoospore infects root tissue and becomes a uninucleate plasmodium. This plasmodium undergoes mitotic nuclear division (creates many nuclei within a single cell) and turns into a multinucleate plasmodium. Then, the multinucleate plasmodium forms zoosporangium, which eventually release more zoospores. This process can happen relatively quickly and can act as an important source of secondary inoculum within a field. [7]

Sexual Stage: This stage follows a similar pattern to the asexual stage, but with a few exceptions. It is hypothesized that two zoospores fuse together to form a dikaryotic zoospore (with two separate haploid nuclei, n+n) and then infect the roots. Once the infection occurs, the dikaryotic zoospore develops into a binucleate plasmodium (one pair on nuclei, n+n). Similar to the asexual stage, this plasmodium will also replicate its nucleus to create a multinucleate plasmodium (many pairs of nuclei, n+n). The second main different between stages occurs here. The pairs of nuclei (n+n) will fuse by karyogamy, and the plasmodium will quickly divide into numerous resting spores within a sporosori (spore sack, alternatively called cystosori). These resting spores have three-layered walls and are extremely resistant to the environment, allowing them to persist in the soil for longer than 10 years. [7]

As a reminder, most of the life cycle is still unclear. However, the presence of zoospores, plasmodia, zoosporangia, and resting spores have been observed in the field and lab. [8] The ploidy levels and karyogamy events are only theorized and have yet to be proven.

Environment

Spongospora subterranea pathogenesis is most effective in cool, damp environments, such as northern Britain, the Columbia Basin of south-central Washington, and north-central Oregon. [6] The environmental condition is particularly critical during the release of infective agents (zoospores) into the soil-environment . Upon release from resting spores, zoospores require moisture to swim towards the host tuber or roots. [9] One study, found powdery scab was significantly more common on plants grown in constant dampness compared to plants grown with varying moisture levels. [10] In this same study it was concluded that disease risk was related more to the environment, or moisture level, than the level of inoculum present. Inoculum may be present but not able to disperse due to environmental conditions, and therefore does not reach host tissue to infect. Other environmental factors that affect Spongospora subterranea infection are directly related to agronomic practices. Increased use of fertilizers containing nitrate or ammonium nitrogen increase the incidence and severity of powdery scab. [11] It is thought that the fertilization increases root growth, and thus provides more tissue for infection and disease cycling to occur. Also, reduced cellulose within the cell walls caused by excess nitrogen may increase susceptibility of host to infection. It is apparent that the environment can directly affect both the host susceptibility and the dispersal of the pathogen ultimately setting the pace for the disease cycle.

Pathogenesis

Potato tuber covered in powdery scabs Powdery scab tuber external.jpg
Potato tuber covered in powdery scabs

S. subterranea is an obligate parasite phytomyxea [12] that infects the below ground structures of the host. Infection leads to hypertrophy and hyperplasia of the host cells and eventual bursting. [13] However, the mechanism behind this is still unknown. [10] Zoospores infect the root hairs by attaching to the outer surface, encysting, and then penetrating the epidermis through lenticels and stomata. [14] Once inside, the multinucleate plasmodium divides to spread and produce more zoospores. The plasmodium causes the infected host cells to multiply rapidly and enlarge into a gall. This rapid multiplication also produces uninucleate cells that aggregate together as sporosori. [13] The sporosori look like a powdery mass within the gall, which gives this disease its name. [15] Eventually the gall swells and bursts out the epidermis of the tuber, releasing the spores back into the soil. Gall severity depends on inoculum level, environment, and potato skin type. Infection is most prevalent in the early stages of tuber formation while the potato tissue is unsuberized. [13] But, infection can occur at all stages on development. White and red skinned potatoes and highly susceptible while russet skinned are somewhat resistant. [16] Russet skin is thicker and has higher levels of the LOX protein which is used as a marker for resistance. [6] There is little known about variation and sexual recombination within S. subterranea, therefore high priority is given to researching the variations within potato cultivars for researching host/pathogen relationships and management. [17]

Importance

Powdery Scab has important implications for commercial farming. Not only does the pathogen itself cause harm, but the pathogen is also a vector for potato mop-top virus, another plant pathogen. As a result, its presence greatly threatens potato marketability for farmers. The burst pustules can also act as a wound for other fungi to infect, such as Phytophthora erythroseptica and Phytophthora infestans . Thus, tubers with powdery scab can have increased incidences of other devastating diseases, including pink rot, dry rot, black dot, and late blight. [6] Potato tubers will form powdery scab pustules that inhibit their ability to be sold. Many markets decline to buy potatoes with ugly scarring even if they are safe to eat. Research has not yet found an effective way to peel the scabs without damaging the potato. [6] Potatoes that are rejected for sale create a large financial burden on farmers. [16] Additionally, because soil borne inoculum can survive for years as spores, the pathogen is very difficult to eliminate once present. In Great Britain a recent Potato Council funded diagnostic project discovered that as much as 82% of fields tested positive for soil inoculum. [6]

Management

S. subterranea currently has no effective chemical controls. Therefore, other cultural management techniques must be used. Using certified clean seeds and planting in fields that have been historically healthy is the best form of control. [18] These methods may prevent infestation from resting spores. Since infection is promoted by cool soil temperatures and high soil moisture, delayed planting can also help reduce negative effects of the pathogen. Delayed planting reduces the growth period in cooler soils subsequently decreasing germination of the spores. One limitation to this method is an additional decrease of early market yield. [16] Pre-planting chemigation with metam sodium can reduce the propagules of the pathogen. [16] Other common means of control include using resistant potatoes and crop rotations. Several cultivars of resistant potatoes include Granola, Nicola, Ditta, and Gladiator. [19] Because soil-borne inoculum can survive for many years, crop rotations should involve alternate species that will promote a partial life cycle of the pathogen. This way the zoospores will germinate without producing new spores. [20] Researchers have investigated the use of beta-aminobutyric acid (BABA) in promoting potato resistance. BABA triggers a plants systemic acquired resistance (SAR), a natural plant defense mechanism. When potatoes are inoculated with BABA and then later inoculated with the pathogen, S. subterranea, they exhibit overall reduction in disease. While pathogen reduction has been experimentally supported, further experimentation needs to be performed. [4] Genomic data inclusive a genome draft became recently available, that might hold information that can be used to improve disease management. [21]

Related Research Articles

<span class="mw-page-title-main">Oomycete</span> Fungus-like eukaryotic microorganism

The Oomycetes, or Oomycota, form a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms within the Stramenopiles. They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the result of contact between hyphae of male antheridia and female oogonia; these spores can overwinter and are known as resting spores. Asexual reproduction involves the formation of chlamydospores and sporangia, producing motile zoospores. Oomycetes occupy both saprophytic and pathogenic lifestyles, and include some of the most notorious pathogens of plants, causing devastating diseases such as late blight of potato and sudden oak death. One oomycete, the mycoparasite Pythium oligandrum, is used for biocontrol, attacking plant pathogenic fungi. The oomycetes are also often referred to as water molds, although the water-preferring nature which led to that name is not true of most species, which are terrestrial pathogens.

<span class="mw-page-title-main">Fusarium wilt</span> Fungal plant disease

Fusarium wilt is a common vascular wilt fungal disease, exhibiting symptoms similar to Verticillium wilt. This disease has been investigated extensively since the early years of this century. The pathogen that causes Fusarium wilt is Fusarium oxysporum. The species is further divided into formae speciales based on host plant.

<span class="mw-page-title-main">Phytomyxea</span> Class of protists

The Phytomyxea are a class of parasites that are cosmopolitan, obligate biotrophic protist parasites of plants, diatoms, oomycetes and brown algae. They are divided into the orders Plasmodiophorida and Phagomyxida. Plasmodiophorids are best known as pathogens or vectors for viruses of arable crops.

<span class="mw-page-title-main">Clubroot</span> Common fungal disease of plants of the family Brassicaceae

Clubroot is a common disease of cabbages, broccoli, cauliflower, Brussels sprouts, radishes, turnips, stocks, wallflowers and other plants of the family Brassicaceae (Cruciferae). It is caused by Plasmodiophora brassicae, which was once considered a slime mold but is now put in the group Phytomyxea. It is the first phytomyxean for which the genome has been sequenced. It has as many as thirteen races. Gall formation or distortion takes place on latent roots and gives the shape of a club or spindle. In the cabbage such attacks on the roots cause undeveloped heads or a failure to head at all, followed often by decline in vigor or by death. It is an important disease, affecting an estimated 10% of the total cultured area worldwide.

<span class="mw-page-title-main">Spraing</span> Disease of potatoes

Spraing is a collective term for diseases and disorders of potato tubers that cause brown streaks in the flesh of the potato. Spraing can be caused by two viruses, tobacco rattle virus (TRV) which is transmitted by trichodorid nematodes, or Potato mop-top virus (PMTV) transmitted by the powdery scab fungus Spongospora subterranea. The two viruses may have synergistic effects in disease progression when both are present. Spraing like symptoms can also be caused by physiological defects or specific nutrient deficiencies, most notably Calcium.

<i>Synchytrium endobioticum</i> Species of fungus

Synchytrium endobioticum is a chytrid fungus that causes the potato wart disease, or black scab. It also infects some other plants of the genus Solanum, though potato is the only cultivated host.

This is a glossary of some of the terms used in phytopathology.

<i>Phytophthora cactorum</i> Species of single-celled organism

Phytophthora cactorum is a fungal-like plant pathogen belonging to the Oomycota phylum. It is the causal agent of root rot on rhododendron and many other species, as well as leather rot of strawberries.

Phytophthora nicotianae or black shank is an oomycete belonging to the order Peronosporales and family Peronosporaceae.

<i>Phytophthora erythroseptica</i> Species of single-celled organism

Phytophthora erythroseptica—also known as pink rot along with several other species of Phytophthora—is a plant pathogen. It infects potatoes causing their tubers to turn pink and damages leaves. It also infects tulips (Tulipa) damaging their leaves and shoots.

<i>Albugo</i> Genus of plant-parasitic oomycetes

Albugo is a genus of plant-parasitic oomycetes. Those are not true fungi (Eumycota), although many discussions of this organism still treat it as a fungus. The taxonomy of this genus is incomplete, but several species are plant pathogens. Albugo is one of three genera currently described in the family Albuginaceae, the taxonomy of many species is still in flux.

<i>Alternaria solani</i> Species of fungus

Alternaria solani is a fungal pathogen that produces a disease in tomato and potato plants called early blight. The pathogen produces distinctive "bullseye" patterned leaf spots and can also cause stem lesions and fruit rot on tomato and tuber blight on potato. Despite the name "early," foliar symptoms usually occur on older leaves. If uncontrolled, early blight can cause significant yield reductions. Primary methods of controlling this disease include preventing long periods of wetness on leaf surfaces and applying fungicides. Early blight can also be caused by Alternaria tomatophila, which is more virulent on stems and leaves of tomato plants than Alternaria solani.

<i>Plasmopara halstedii</i> Species of single-celled organism

Plasmopara halstedii is a plant pathogen infecting sunflowers. The species is one of many pathogens commonly referred to as downy mildew. P. halstedii originated in North America.

Phytophthora megakarya is an oomycete plant pathogen that causes black pod disease in cocoa trees in west and central Africa. This pathogen can cause detrimental loss of yield in the economically important cocoa industry, worth approximately $70 billion annually. It can damage any part of the tree, causing total yield losses which can easily reach 20-25%. A mixture of chemical and cultural controls, as well as choosing resistant plant varieties, are often necessary to control this pathogen.

Sphaceloma arachidis is a plant pathogen infecting peanuts.

<i>Colletotrichum coccodes</i> Pathogenic fungus

Colletotrichum coccodes is a plant pathogen, which causes anthracnose on tomato and black dot disease of potato. Fungi survive on crop debris and disease emergence is favored by warm temperatures and wet weather.

<i>Septoria malagutii</i> Species of fungus

Septoria malagutii is a fungal plant pathogen infecting potatoes. The casual fungal pathogen is a deuteromycete and therefore has no true sexual stage. As a result, Septoria produces pycnidia, an asexual flask shaped fruiting body, on the leaves of potato and other tuber-bearing spp. causing small black to brown necrotic lesions ranging in size from 1-5mm. The necrotic lesions can fuse together forming large necrotic areas susceptible to leaf drop, early senescence, dieback, and dwarfing. Septoria malagutii has been found only in the Andean countries of Bolivia, Ecuador, Peru, and Venezuela at altitudes of near 3000 meters. Consequently, the fungi grows and disperses best under relatively low temperatures with high humidities, with optimal growth occurring at 20 °C (68 °F). The disease has caused devastation on potato yields in South America and in areas where this disease is common, potato yields have been seen to drop by 60%.

<i>Helminthosporium solani</i> Species of fungus

Helminthosporium solani is a fungal plant pathogen responsible for the plant disease known as silver scurf. 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." There are some reports of it affecting development, meaning growth and tuber yield. 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. The disease has become economically important because silver scurf affected potatoes for processing and direct consumption have been rejected by the industry. 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. There are multiple ways to help control the disease.

Potato mop-top virus (PMTV) is a plant pathogenic virus transmitted through the vector Spongospora subterranea that affects potatoes. PMTV belongs to family of Virgaviridae, and the genus Pomovirus. The virus was first identified in 1966 by Calvert and Harrison in Britain, and is now reported in many other potato cultivating regions of the world including U.S.A., Canada, China, Pakistan, Japan, South American countries and many parts of Europe. Many disease management systems have been found to be ineffective against the virus, although a combination of sanitation and vector controls seems to work well.

<span class="mw-page-title-main">Common scab</span> Plant disease affecting potatoes and other crops

Common scab is a plant disease of root and tuber crops caused by a small number of Streptomyces species, specifically S. scabies, S. acidiscabies, S. turgidiscabies and others. Common scab mainly affects potato, but can also cause disease on radish, parsnip, beet, and carrot. This plant disease is found wherever these vegetables are grown.

References

  1. ↑ "Resistance to Powdery Scab in Potatoes" (PDF). USDA/ARS. Retrieved 2015-11-11.
  2. ↑ "Potato scabs/RHS Gardening". www.rhs.org.uk. Retrieved 2015-11-11.
  3. ↑ Schwelm A, Badstöber J, Bulman S, Desoignies N, Etemadi M, Falloon RE, Gachon CM, Legreve A, Lukeš J, Merz U, Nenarokova A, Strittmatter M, Sullivan BK, Neuhauser S (April 2018). "Not in your usual Top 10: protists that infect plants and algae". Molecular Plant Pathology. 19 (4): 1029–1044. doi:10.1111/mpp.12580. PMC   5772912 . PMID   29024322.
  4. 1 2 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.
  5. ↑ "Bulletin #2436, Powdery Scab of Potatoes | Cooperative Extension Publications | University of Maine". umaine.edu. Retrieved 2015-11-11.
  6. 1 2 3 4 5 6 Dennis A. Johnson and Thomas F. Cummings. Effect of Powdery Scab Root Galls on Yield of Potato. (2015).Plant Disease 99:10, 1396-1403
  7. 1 2 Merz, Ueli (2008-04-16). "Powdery Scab of Potato—Occurrence, Life Cycle and Epidemiology". American Journal of Potato Research. 85 (4): 241–246. doi:10.1007/s12230-008-9019-1. hdl: 20.500.11850/9544 . ISSN   1099-209X. S2CID   38001426.
  8. ↑ Qu, Xinshun; Christ, Barbara J. (2007-12-01). "In vitro culture of the obligate parasite Spongospora subterranea (cercozoa; plasmodiophorida) associated with root-inducing transferred-DNA transformed potato hairy roots". The Journal of Eukaryotic Microbiology. 54 (6): 465–467. doi:10.1111/j.1550-7408.2007.00289.x. ISSN   1066-5234. PMID   18070323. S2CID   8842628.
  9. ↑ Balendres, M. A.; Tegg, R. S.; Wilson, C. R. (2016-02-05). "Key events in pathogenesis of spongospora diseases in potato: a review". Australasian Plant Pathology. 45 (3): 229–240. Bibcode:2016AuPP...45..229B. doi:10.1007/s13313-016-0398-3. ISSN   0815-3191. S2CID   13658887.
  10. 1 2 Lees, Alison K.; Graaf, Pieter van de; Wale, Stuart (2008-04-23). "The Identification and Detection of Spongospora subterranea and Factors Affecting Infection and Disease". American Journal of Potato Research. 85 (4): 247–252. doi:10.1007/s12230-008-9018-2. ISSN   1099-209X. S2CID   29987047.
  11. ↑ Shah, Farhat A.; Falloon, Richard E.; Butler, Ruth C.; Lister, Ros A.; Thomas, Steve M.; Curtin, Denis (2014-09-17). "Agronomic factors affect powdery scab of potato and amounts of Spongospora subterranea DNA in soil". Australasian Plant Pathology. 43 (6): 679–689. Bibcode:2014AuPP...43..679S. doi:10.1007/s13313-014-0317-4. hdl: 10182/10430 . ISSN   0815-3191. S2CID   18388456.
  12. ↑ Schwelm, Arne; Badstöber, Julia; Bulman, Simon; Desoignies, Nicolas; Etemadi, Mohammad; Falloon, Richard E.; Gachon, Claire M. M.; Legreve, Anne; Lukeš, Julius; Merz, Ueli; Nenarokova, Anna; Strittmatter, Martina; Sullivan, Brooke K.; Neuhauser, Sigrid (2018). "Not in your usual Top 10: Protists that infect plants and algae". Molecular Plant Pathology. 19 (4): 1029–1044. doi: 10.1111/mpp.12580 . PMC   5772912 . PMID   29024322.
  13. 1 2 3 Wale, Stuart; Platt, Bud; Cattlin, Nigel D. (2008-04-11). Diseases, Pests and Disorders of Potatoes: A Colour Handbook. CRC Press. ISBN   9781840765083.
  14. ↑ Jones, D.G. (2013). The Epidemiology of Plant Diseases. Springer Science & Business Media. pp. 108–109. ISBN   978-9401733021.
  15. ↑ "Powdery Scab | AHDB Potatoes". potatoes.ahdb.org.uk. Archived from the original on 2015-06-25. Retrieved 2015-10-22.
  16. 1 2 3 4 "How to Manage Pests." UC IPM: UC Management Guidelines for Powdery Scab on Potato. N.p., n.d. Web. 19 Oct. 2015.
  17. ↑ Merz, U.; Falloon, R. E. (2008-09-26). "Review: Powdery Scab of Potato—Increased Knowledge of Pathogen Biology and Disease Epidemiology for Effective Disease Management". Potato Research. 52 (1): 17–37. doi:10.1007/s11540-008-9105-2. hdl: 20.500.11850/380051 . ISSN   0014-3065. S2CID   37670848.
  18. ↑ Gudmestad, Neil. "Potential Management of Powdery Scab and Mop Top Virus Using an Integration of Soil Fumigation and Genetic Resistance" (PDF). Department of Plant Pathology, North Dakota State University, Fargo, ND. Archived from the original (PDF) on 2015-12-08. Retrieved 2015-10-22.
  19. ↑ C. R. Brown, G. Vandemark, D. Johnson, Tom Cummings, Dallas Batchelor, Jeff Miller, Chris Olsen. Resistance to Powdery Scab in Potato. Web. 11 Nov. 2015.
  20. ↑ Nitzan, Nadav, Dennis Johnson, Dallas Batchelor, and Chuck Brown. "Powdery Scab." Potato Country (2007): 6-7. Print.
  21. ↑ Ciaghi S, Neuhauser S, Schwelm A (2018). "Draft Genome Resource for the Potato Powdery Scab Pathogen Spongospora subterranea". Molecular Plant-Microbe Interactions. 31 (12): 1227–1229. doi:10.1094/MPMI-06-18-0163-A. PMC   6443038 . PMID   29969057.
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