Pythium irregulare

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Pythium irregulare
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Stramenopiles
Phylum: Oomycota
Order: Peronosporales
Family: Pythiaceae
Genus: Pythium
Species:
P. irregulare
Binomial name
Pythium irregulare
Buisman, (1927)

Pythium irregulare is a soil borne oomycete plant pathogen. [1] Oomycetes, also known as "water molds", are fungal-like protists. They are fungal-like because of their similar life cycles, but differ in that the resting stage is diploid, they have coenocytic hyphae, a larger genome, cellulose in their cell walls instead of chitin, and contain zoospores (asexual motile spores) and oospores (sexual resting spores). [2]

Contents

Hosts and symptoms

Pythium irregulare is an oomycete that causes pre- and post-emergence damping off, as well as root rot. [1] Pre-emergence damping off occurs when P. irregulare infects seeds before they emerge, causing them to rot and turn brown, thus preventing successful growth. [1] [3] Alternatively, post-emergence damping off occurs when the oomycete infects just after the seed has germinated. [1] [3] This usually causes infection in the roots and stem which appears as water soaking and necrosis. [1] [3] Depending on the severity, plants may collapse or be severely stunted. [1] In plants that are older and more established, P. irregulare causes root rot. [3] This will initially cause necrotic lesions, which leads to chlorosis, reduced yield, poor growth, and stunting due to inadequate water and nutrient acquisition by the roots. [1] Additionally, P. irregulare is often found coinfecting with other Pythium species. [1] All three of these diseases caused by P. irregulare can be caused by other pathogens as well, so a disease diagnosis is not necessarily indicative of P. irregulare [4]

In order to identify Pythium irregulare it is necessary to isolate the organism and observe it microscopically. First, it is important to identify that the microbe is an oomycete by looking for characteristics that are specific to oomycetes, such as coenocytic hyphae, zoospores, and oospores. [2] After that, one can identify the microbe as being in the genera Pythium by observing disease symptoms, host range, as well as the presence of a vesicle, where zoospores form, which is attached to the sporangia. [5] In contrast, most other oomycetes do not have a vesicle and the zoospores form in the sporangia. [5] Finally, once the genera has been identified, it is helpful to use a dichotomous key to identify the species. [6] Some of the key identifiers for P. irregulare include oogonia with irregular shaped, cylindrical projections, sporangia that occur singly, sporangia that are not filamentous, and oogonia smaller than 30 μm. [7] There are also many genomic tests that can be done to determine species based on specific DNA markers. [8] It is also important to note that many diagnosticians do not identify to the species level because it can be difficult to find all necessary microscopic structures and many management techniques can be applied to all Pythium species. [8] [9]

Pythium irregulare has a very broad host range, including many agronomically and horticulturally important crops and is found on every continent except for Antarctica. [1] P. irregulare infects over 200 species, including cereals, legumes, fruits, vegetables, and ornamentals. [1] It differs from many other Pythium species in that it prefers cooler environments. [1] [3] A moist environment is also necessary for disease, which aids motility of spores. [1] [3] It is commonly found in both greenhouses and fields. [1] [4] [9]

Disease cycle

Pythium irregulare, like most oomycetes, has a life cycle with sexual and asexual stages. [1] During the winter, oospores, which are sexual resting spores, survive in the soil. [1] [9] Oospore germination occurs when the oospore senses chemicals released by seeds or roots. [1] Once germinated, oospores can produce either a germ tube, which directly infects the plant, or a sporangium, which releases zoospores that infect the plant. [1] [9] Sporangium that produce zoospores make up the asexual phase of the life cycle. The zoospores can move through soil when water is present, which is why water is important for disease to occur. [1] Once zoospores reach the root or seed, they encyst, germinate, and infect via a germ tube. [1] [9] Once infection has been established, the pathogen grows hyphae both in and outside the plant and releases enzymes to breakdown plant tissue. [1] [9] The breakdown of tissue provides nutrients for the pathogen, also known as necrotrophy. [9] Once the plant dies, more sporangium can form, release zoospores, and repeat the infection cycle. [9] Alternatively, the hyphae within the dead plant material may also continue to grow and develop “male” and “female” haploid mating structures, known as antheridium and oogonium, respectively. [1] The antheridium then transfers its genetic material to the oogonium (fertilization), resulting in the diploid oospore, which overwinters and starts the infection over again in the spring. [1]

Pythium irregulare Life Cycle.png

Management

Pythium irregulare requires very specific environmental conditions to produce disease, so control of environment is the first step. [10] Because the zoospores require water to be able to move around, preventing standing water will decrease the chance of disease occurrence. [10] Additionally, excess water can lead to an increase in insects that feed on roots, making it easier for the pathogen to spread, as it can make its way into the plant through wounds. [9] Water levels can be controlled by avoiding planting in areas that have poor drainage and controlling irrigation as to not overwater plants. [9] [10] Because P. irregulare has oospores that survive under harsh conditions, sanitation is very important to limit the spread. [9] [10] Contaminated irrigation systems, tools, and seeds can spread the disease, so disinfection with heat or chemicals are necessary to prevent further spread, as well as purchasing certified clean seed. [4] [9] [10] [11] Additionally, in greenhouses scenarios it is important to sanitize soil, work benches, and tools with heat or chemicals as well. [4] [9] [10] It is also important to avoid over-fertilizing plants, as fertilizers can suppress plant defenses and damage roots, making it easier for P. irregulare to infect. [9] Finally, if you have had previous problems with Pythium irregulare, you can take preventative measures by mixing fungicides into the soil, although this is more easily achieved in a greenhouse scenario. [9] [10] It is important to create a fungicide plan with different rotations of fungicides if you choose to prevent disease this way in order to prevent the pathogen from becoming resistant to the fungicide. [9] Some fungicides used to prevent P. irregulare include mefenoxam, fosetyl-Al, and etridiazole. [9] [10] Additionally, certain biological agents such as Trichoderma harzianum and Gliocladium virens can be used as biological control measures to prevent infection; however, this is also a more plausible control method in a greenhouse, again because it needs to be mixed into the soil. [10] Crop rotation is not necessarily a good option for P. irregulare control because many crops are viable hosts, oospores can survive in the soil for many years, and the pathogen can survive on organic matter; however, rotation with a non-host crop may be able to reduce the pathogen load, thus decreasing infection in subsequent years [12]

See also

Related Research Articles

Phytophthora sojae is an oomycete and a soil-borne plant pathogen that causes stem and root rot of soybean. This is a prevalent disease in most soybean growing regions, and a major cause of crop loss. In wet conditions the pathogen produces zoospores that move in water and are attracted to soybean roots. Zoospores can attach to roots, germinate, and infect the plant tissues. Diseased roots develop lesions that may spread up the stem and eventually kill the entire plant. Phytophthora sojae also produces oospores that can remain dormant in the soil over the winter, or longer, and germinate when conditions are favourable. Oospores may also be spread by animals or machinery.

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

Phytophthora palmivora is an oomycete that causes bud-rot of palms, fruit-rot or kole-roga of coconut and areca nut. These are among the most serious diseases caused by fungi and moulds in South India. It occurs almost every year in Malnad, Mysore, North & South Kanara, Malabar and other areas. Similar diseases of palms are also known to occur in Sri Lanka, Mauritius, and Sumatra. The causative organism was first identified as P. palmivora by Edwin John Butler in 1917.

Aphanomyces euteiches is a water mould, or oomycete, plant pathogen responsible for the disease Aphanomyces root rot. The species Aphanomyces euteiches can infect a variety of legumes. Symptoms of the disease can differ among hosts but generally include reduced root volume and function, leading to stunting and chlorotic foliage. Aphanomyces root rot is an important agricultural disease in the United States, Europe, Australia, New Zealand, and Japan. Management includes using resistant crop varieties and having good soil drainage, as well as testing soil for the pathogen to avoid infected fields.

<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.

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

Phytophthora medicaginis is an oomycete plant pathogen that causes root rot in alfalfa and chickpea. It is a major disease of these plants and is found wherever they are grown. P. medicaginis causes failure of stand establishment because of seedling death. Phytophthora medicaginis is part of a species complex with Phytophthora megasperma.

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

Pythium ultimum is a plant pathogen. It causes damping off and root rot diseases of hundreds of diverse plant hosts including corn, soybean, potato, wheat, fir, and many ornamental species. P. ultimum belongs to the peronosporalean lineage of oomycetes, along with other important plant pathogens such as Phytophthora spp. and many genera of downy mildews. P. ultimum is a frequent inhabitant of fields, freshwater ponds, and decomposing vegetation in most areas of the world. Contributing to the widespread distribution and persistence of P. ultimum is its ability to grow saprotrophically in soil and plant residue. This trait is also exhibited by most Pythium spp. but not by the related Phytophthora spp., which can only colonize living plant hosts.

<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.

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Pythium graminicola is a plant pathogen infecting cereals.

Pythium myriotylum is a soil-borne oomycete necrotroph that has a broad host range, this means that it can infect a wide range of plants.

Pythium volutum is a plant pathogen infecting wheat, barley, and turfgrass. It is known to be sensitive to some of the compounds typically present in selective media commonly used for isolating Pythium spp., so isolation may require alternative methods.

Sclerophthora macrospora is a protist plant pathogen of the class Oomycota. It causes downy mildew on a vast number of cereal crops including oats, rice, maize, and wheat as well as varieties of turf grass. The common names of the diseases associated with Sclerophthora macrospora include "crazy top disease" on maize and yellow tuft disease on turf grass. The disease is present all over the world, but it is especially persistent in Europe.

<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.

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Black rot on orchids is caused by Pythium and Phytophthora species. Black rot targets a variety of orchids but Cattleya orchids are especially susceptible. Pythium ultimum and Phytophthora cactorum are known to cause black rot in orchids.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Katawczik, Melanie. "Pythium irregulare". projects.ncsu.edu. North Carolina State University, College of Agriculture and Life Sciences, Department of Plant Pathology. Archived from the original on 2016-12-20. Retrieved 2016-12-06.
  2. 1 2 Judelson, Howard S.; Blanco, Flavio A. (2005-01-01). "The spores of Phytophthora: weapons of the plant destroyer". Nature Reviews Microbiology. 3 (1): 47–58. doi:10.1038/nrmicro1064. ISSN   1740-1526. PMID   15608699. S2CID   28560256.
  3. 1 2 3 4 5 6 Moorman, Gary; May, Sara. "Disease Caused by Pythium". plantpath.psu.edu/pythium/. Penn State, College of Agricultural Sciences, Department of Plant Pathology and Environmental Microbiology. Retrieved 2016-12-06.
  4. 1 2 3 4 "Pythium". extension.psu.edu/pests/plant-diseases/all-fact-sheets/pythium. Penn State College of Agricultural Sciences Extension. Retrieved 2016-12-06.
  5. 1 2 Heffer Link, Virginia; Powelson, Mary; Johnson, Kenneth. "Oomycetes". The American Phytopathological Society. Archived from the original on 2016-11-22. Retrieved 2016-12-06.
  6. ↑ http://plantpath.psu.edu/pythium/module-3/plaats-niterink-key-pythium [ bare URL PDF ]
  7. ↑ Plaats-Niterink, A.J. van der. "Key to the Species of Pythium". Penn State University. Retrieved 2016-12-06.
  8. 1 2 "Pythium Genome Database". Michigan State University. Archived from the original on 2010-06-14. Retrieved 2016-12-06.
  9. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Beckerman, Janna. "Pythium Root Rot of Herbaceous Plants" (PDF). Disease Management Strategies for Horticultural Crops. Purdue Agricultural Communication. Retrieved 2016-12-05.
  10. 1 2 3 4 5 6 7 8 9 "Pythium Root Rot". University of California Pest Management Guidelines. University of California Agriculture and Natural Resources. Retrieved 2016-12-06.
  11. ↑ "Disease Alert: Pythium". Syngenta. Retrieved 2016-12-05.
  12. ↑ McGrath, Margaret. "Managing Plant Diseases With Crop Rotation". www.sare.org. Sustainable Agriculture Research and Education. Retrieved 2016-12-06.
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