Phytophthora Erythroseptica
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''Phytophthora erythroseptica''—also known as pink rot along with several other species of '' Phytophthora''—is a plant pathogen. It infects potatoes ('' Solanum tuberosum'') causing their tubers to turn pink and damages leaves. It also infects tulips ('' Tulipa'') damaging their leaves and shoots. Several species from the genus ''Phytophthora'' are believed to be involved in causing pink rot-like diseases.


Disease cycle

As ''Phytophthora erythroseptica'' is an oomycete, its disease cycle follows that of similar ''Phytophthora'' species. Oospores, sporangia, and zoospores can infect any part of the potato plant that is below ground. Oospores serve as the primary form of inoculum, and can survive in the soil as long as seven yearsWarton, Phillip., Kirk, William. Potato Diseases: Pink Rot (E2993). 31 January 2017. Michigan State University Extension http://msue.anr.msu.edu/resources/potato_diseases_pink_rot_e2993 Oospores produced in the field can overwinter and when thawed produce an
oogonium An oogonium (plural oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes. In the mammalian fetus Oogonia are formed in larg ...
and antheridium which will then lead to the production of sporangia, oospores, and zoospores. This pathogen can be polycyclic, using sporangia as the secondary inoculum. Often this secondary inoculum infects tubers post harvest while in storage. Zoospores are motile asexual spores that can move through soil water through the use of their
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 ...
. These zoospores are also capable of encysting and infecting below ground plant tissue.


Environmental conditions

Environmental factors play a critical role in the development and spread of ''P. erythroseptica'' on a field scale. This pathogen grows best in a warm and wet environment. It can infect a host without a wound, however the presence of a wound will increase infection greatly. A wound is needed for infection to occur when the tubers are in storage. Very moist fields will have increased rates of infection as the amount of moisture makes it easy for the zoospores to move through the soil and infect tubers. Avoiding excessive late-season irrigation is imperative to minimize the risk for infection developing in the field. Avoiding excess free moisture is also important when storing potatoes after harvest. Soil moisture levels that are close to field capacity, whether the water comes from rainfall or irrigation, have been shown to increase the likelihood of soil-borne diseases. This pathogen can also survive year to year as oospores in moist soil conditions, and also in volunteer potatoes or cull piles. Also, ''P. erythroseptica'' can germinate rapidly in warm soil conditions, thriving at temperatures around .


Symptoms and host

''P. erythroseptica'' is host specific, and typically only infects potatoes in moist soils. However, there are related pink rot species that infect raspberries, tomatoes, clover, and asparagus. Symptoms of the disease in potatoes can be seen on the tubers, above ground vegetation, as well as the roots of the potatoes. Tuber symptoms are the most obvious to diagnose. Occasionally, a darkened color can be observed on the skin covering the infected portion of the tuber. When a suspected tuber is cut open, a dividing line can be seen between the healthy tuber tissue and the infected tissue. Infection spreads from the
stolon In biology, stolons (from Latin '' stolō'', genitive ''stolōnis'' – "branch"), also known as runners, are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external s ...
end of tubers and usually leads to a rubbery or spongy consistency. Pink rot is not considered a slimy soft rot, since most of the tissue stays intact The pinkish-salmon color of infected tubers can be seen once the phenolic compounds inside the tubers are exposed to oxygen for 15–30 minutes. After this time period the infected tissue turns to a brownish-blackish color Aboveground symptoms can include chlorosis, stunting, and wilting of the plants. Roots and stolons can become blackened as well. The pink color is often used as the main symptom when making a firm diagnosis. The infected tubers often are watery and have a distinct smell. The potatoes plants themselves can sometimes be wilted however most symptoms are seen on the tuber. The majority of diseased tubers get infected while in storage. The majority of symptoms are seen inside the tuber except for the rubbery appearance that the outside may have. There are often cases that show symptoms other than rotting, these are often due to a pathogen other than ''P. erythroseptica'' infecting the tuber along with pink rot.


Management

A multi-faceted approach is recommended to control pink rot. Sanitation of fields to reduce the amount of residues and volunteer potatoes is important to remove sources of inoculum or places the pathogen can overwinter. A crop rotation of 3–4 years is recommended to limit the amount of surviving spores in the soil, which is the main form of inoculum. Most cultivars of potatoes currently in production are susceptible to pink rot; however, some are more resistant than others. Varieties that are particularly susceptible are Dark Red Norland, Red LaSoda, Russet Norkotah, and Snowden. Some cultivars with better resistance are Atlantic, FL-1900, and
Ranger Russet The Ranger Russet is a late-maturing potato that is used for baking and processing into fries. It was originally bred by Joseph J. Pavek of the USDA in Aberdeen, Idaho,Paul R. Wonning and released jointly by the USDA and the agricultural statio ...
. In areas that Pink Rot is known to occur, it is best to avoid extremely susceptible cultivars. Additionally, planting only certified seed, avoiding recently problematic fields, and monitoring soil moistures and conditions, are all recommended practices when planting potatoes. It is not recommended to plant potatoes when fields are wet, or in low spots that can retain water for lengthy periods. Careful and thoughtful harvesting is important to minimize the risk of disease development. This includes allowing a good skin set before harvest, minimizing damage while harvesting, avoiding harvesting potatoes from wet areas that are more susceptible or likely to be diseased, and avoid harvesting in temperatures greater than . Curing potatoes in conditions of high humidity and cool temperatures to promote wound healing, and storing potatoes with adequate air movement and cool temperatures can also help prevent disease. Chemical control can be difficult due to resistance development to some
fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...
s. Also there are few fungicidal modes of action that are effective. This includes the formerly successful metalaxyl, which is now widely ineffective due to resistance exhibited in the pathogen. Mefenoxam is another fungicide that pink rot pathogens have shown resistance against. However, research has shown that a combination of mefenoxam and
oxathiapiprolin Oxathiapiprolin (trade names Orondis, Zorvec, and Segovis) is a fungicide. In the United States, the Environmental Protection Agency has approved it for use against several fungal diseases including downy mildew and various ''Phytophthora'' spe ...
has demonstrated effectiveness on suppressing pink rot. There have been studies done on phosphorous acid (Phostrol) as a systemic and contact fungicide against pink rot, but the exact mode of action has not yet been determined. Fluopicolide, part of the benzamide class of fungicides, has been shown to be effective at reducing pink rot on field scales.Zhang, Xuemei (Missi). Chemical and Non-Chemical Control of Potato Pink Rot. 15 December 2016. The University of Maine Digital Commons. http://digitalcommons.library.umaine.edu/cgi/viewcontent.cgi?article=3651&context=etd There has not yet been cross-resistance between fluopicolide and mefenoxam, meaning these fungicides can be used rotationally to minimize the development of resistance. Metalaxyl and similar chemicals disrupt
RNA polymerase In molecular biology, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that synthesizes RNA from a DNA template. Using the enzyme helicase, RNAP locally opens the ...
and prevent transcription. These chemicals are often used about a month before harvest. However, resistance to pink rot is being tested and encouraged in new cultivars of potatoes.


References


External links


Index Fungorum

USDA ARS Fungal Database
{{Taxonbar, from=Q3010754 erythroseptica Water mould plant pathogens and diseases Potato diseases Ornamental plant pathogens and diseases