Pythium ultimum

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Pythium ultimum
Systematics
Department : Egg mushrooms (Oomycota)
Class : Oomycetes
Order : Peronosporales
Family : Pythiaceae
Genre : Pythium
Type : Pythium ultimum
Scientific name
Pythium ultimum
Trow, (1901)

Pythium ultimum is a phyto-pathogen from the Pythiaceae family. It belongs to the order of the Peronosporales within the group of egg fungi , together with other important phyto-pathogens such as Phytophthora spp. and other genera thatcause diseases knownas downy mildew . The species causes wilting and root rot in hundreds of plant hosts such as corn , soybeans , potatoes , wheat , fir and many ornamental plants .

ecology

P. ultimum is a common inhabitant of fields, stagnant waters, and rotting vegetation in most areas of the world. Its ability to grow saprophytically in the soil and in plant remains contributes to the wide distribution and persistence of P. ultimum . Most Pythium species have this ability , but not the related Phytophthora species, which can only attack living plants.

Pathology and disease control

Infection of seeds and roots, both through the mycelium and through them spores of P. ultimum initiated. Two types of spores are produced depending on the conditions. P. ultimum is a species complex with two varieties, P. ultimum var. Ultimum and P. ultimum var. Sporangiiferum . The main differentiator is that sporangia and zoospores (floating spores) are only very rarely produced by P. ultimum var. Ultimum . Both varieties produce oospores , which are thick-walled structures produced by sexual recombination; they are both homothallic , which means that a single mycelial thread can reproduce with itself. In addition to the oospores, P. ultimum var. Ultimum also creates swellings of the hyphae , which, similar to sporangia, germinate to form plant-infecting hyphae. An important ecological difference between the two types of spores is that sporangia and zoospores are short-lived, while the thick-walled oospores can survive in the ground for years and can even survive winter frosts.

Mycelia and oospores in the soil can infect seeds and roots. This leads to withering, reduced yield and ultimately death of the plant. General signs of a Pythium infection are stunted plants, brown discoloration of the root tips and wilting of the plant in the warm time of the day. Combating the disease is complicated and includes measures of hygiene , the application of fungicides and biological pest control . Among the used fungicides are metalaxyl (mefenoxam), thiadiazoles , etridiazole , propamocarb , dimethomorph and phosphonates . Agents for biological pest control contain the bacteria Bacillus subtilis and Streptomyces griseoviridis and the fungi Candida oleophila , Gliocladium catenulatum , Trichoderma harzianum and Trichoderma virens .

Real resistance in the host is not available. Hygiene is important because the pathogen can easily be introduced into pasteurized soils or even soil-free pot mixes through dirty tools or pots. In greenhouses in particular, fungus gnats can transmit the pathogen from one place to another. A recent study in greenhouses in Michigan showed that the same populations of the pathogen were responsible for root rot in all ornamental plants over a two-year period. The results underline the importance of hygiene measures and encourage greenhouse owners to examine all purchased plants in order to prevent further infection with root rot.

Taxonomy

The following varieties are described:

  • Pythium ultimum var. Ultimum
  • Pythium ultimum var. Sporangiiferum

The genomes of both varieties were sequenced. Analysis of the genomes suggests that 15,290 and 14,086 proteins are encoded.

Individual evidence

  1. ↑ MW Dick: Straminipilous fungi . Kluwer Academic Publishers, Dordrecht 2001.
  2. ^ DF Farr, AY Rossman: Fungal Databases . Systematic Mycology and Microbiology Laboratory, ARS, USDA .. 2014. Archived from the original on January 30, 2007. Retrieved January 30, 2007.
  3. ↑ KL Schroeder, FN Martin, AWAM de Cock, CA Levesque, CFJ Spies, PA Okubara, et al .: Molecular detection and quantification of Pythium species: evolving taxonomy, new tools, and challenges . In: Plant Dis. . 97, 2013, pp. 4-20. doi : 10.1094 / PDIS-03-12-0243-FE . Retrieved August 6, 2019.
  4. ^ G. Moorman: Root rot can be caused by several different species of the fungus-like organism Pythium . Retrieved August 6, 2019.
  5. ^ Population Structure of Pythium ultimum from Greenhouse Floral Crops in Michigan . In: Plant Disease . American Phytopathological Society. Accessed May 1, 2019.
  6. ↑ BN Adhikari, JP Hamilton, MM Zerillo, N. Tisserat, CA Levesque, CR Buell: Comparative genomics reveals insight into virulence strategies of plant pathogenic oomycetes . In: PLoS ONE . 8, 2013, p. E75072. Retrieved August 6, 2019.
  7. ↑ CA Levesque, H. Brouwer, L. Cano, JP Hamilton, C. Holt, E. Huitema, et al .: Genome sequence of the necrotrophic plant pathogen Pythium ultimum reveals original pathogenicity mechanisms and effector repertoire . In: Genome Biol. . 11, No. R73, 2010. Retrieved August 6, 2019.

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