Pythium aphanidermatum

from Wikipedia, the free encyclopedia
Pythium aphanidermatum
Systematics
Department : Egg mushrooms (Oomycota)
Class : Oomycetes
Order : Peronosporales
Family : Pythiaceae
Genre : Pythium
Type : Pythium aphanidermatum
Scientific name
Pythium aphanidermatum
(Edson) Fitzp.

Pythium aphanidermatum is a soil-borne plant pathogen belonging to the Pythiaceae familywithin the group of egg fungi . These are not real fungi because their cellwallsaremade of cellulose instead of chitin , theyare diploid in the vegetative stage, they have coenocytic hyphae (without cell walls) and are thereforecounted amongthe protists . They reproduce with the help of mobile biflagellate zoospores , which need water in order to be able to move and infect a host. Sexually they reproduce through antheridia , oogonia and oospores .

Taxonomy

The following synonyms are known:

  • Nematosporangium aphanidermatum (Edson) Fitzp.
  • Nematosporangium aphanidermatum subsp. hawaiiense sideris
  • Nematosporangium aphanidermatum var. Aphanidermatum (Edson) Fitzp., 1923
  • Rheosporangium aphanidermatum Edson

Hosts

Pythium aphanidermatum has a broad host range and potentially economic implications for growing soybeans , beets , peppers , chrysanthemums , cucurbits , cotton and grass for turf . However, because P. aphanidermatum requires higher temperatures, the pathogen is often detected in greenhouses and has a major impact on the production of poinsettias . It is the main cause of papaya root rot in subtropical areas. While it is a mostly exclusively plant pathogen, there is one documented case of P. aphanidermatum infection in a person injured in the war in Afghanistan .

Symptoms

Pythium aphanidermatum is responsible for seedling, root, stem and cob rot before or after germination . Before germination, the infection can have poor germination or no germination at all and is visible as browning or rotting of the seeds. After germination, the shoot axis of the plant near the point where it emerges from the ground becomes thin and soaked, which ultimately leads to the plant breaking up. P. aphanidermatum can also cause root rot, which can also manifest itself in dwarfism , bleached leaves , fallen leaves and wilting. The infection begins at the root tip and can cause the protective layers in the infected region to break down so that the inner root is freely accessible to other pathogens.

Disease cycle

Pythium aphanidermatum overwinters in the soil as an oospore, hypha and / or sporangium . Oospores can create a germ tube and infect the plant directly or, if the conditions are suitable (i.e. if there is sufficient water), they can produce sporangia, which in turn release mobile biflagellate zoospores that swim to the host plant, encapsulate (encyst) themselves in it and germinate. This infection can occur on seeds that can themselves produce rotten or weakened seedlings. When the pathogen attacks the roots of a seedling or sapling, the mycelium begins to penetrate the plant tissue and release digestive enzymes that dissolve the host's cell walls, making nutrients available to the pathogen. The plant dies over time. P. aphanidermatum causes polycyclic disease. Such a pathogen goes through several life cycles in one season, which means that it can re-infect the host plant or infect the next plant. A few things can happen after infection that spreads it:

  • Other asexual forms such as sporangiophores and sporangia form, which release further zoospores that re-infect the host plant or migrate to the next plant.
  • Sexual reproduction can occur when two different mating types of hyphae meet, forming an oogon (the female part) and an antheridium (the male part). This ends with genetic recombination and forms an oospore - the permanent stage of the pathogen.

Environmental conditions

Pythium aphanidermatum infects plants with the help of mobile zoospores, and because these have to reach the hosts by swimming, the presence of water promotes the fastest possible spread of the disease. The temperature also has an influence on the spread of the pathogen. It can infect hosts in cooler temperatures (55 ° F (13 ° C) ... 64 ° F (18 ° C)), but conditions between 86 ° F (30 ° C) and 95 ° F (35 ° C) are ideal ), an area that sets it apart from other Pythium species. Potential host plants suffering from stress are more susceptible to infection. Stress-inducing factors that increase the likelihood of infection include: a. high salt concentrations, drought, lack of nutrients and extreme moisture in the immediate vicinity of the plant. High salt levels in the soil can promote infection at temperatures and moisture levels that are suboptimal for the pathogen. Extreme nitrogen fertilization will also increase the likelihood of infection, because the nitrogen weakens the plants' internal defense mechanisms and damages the root ends, which are the main route of infection. In addition, the medium in which the plant grows affects the severity of a Pythium infection. Sterile, soil-less cultures are the most sensitive, while increasing soil levels inhibit the spread of the pathogen through bacteria present in the soil. Finally, seedlings and germinating plants are more sensitive to the pathogen and are often victims of root rot.

management

Several management methods in cultivation can effectively influence diseases caused by Pythium aphanidermatum . The pathogen thrives in a humid environment, so it is important to prevent excessive water content in the growth media. Too frequent irrigation and poorly drained soil are common mistakes that end in infestation. In addition, poor ventilation and inadequate tanning can lead to moisture accumulation in the plant itself, potentially promoting the spread of the disease. Soil hygiene measures and minimizing plant debris in which the pathogen can survive are also effective measures in cultivation.

Fungicides are also effective control methods. Systemic and contact fungicides can be used, but it is best to switch between these classes of substances to avoid resistance of the pathogen. Several classes of chemical substances such as acylalanines ( Furalaxyl ), thiadiazoles , carbamates , cinnamic acid - derivatives , phosphonates and phosphites can be used. In general, these fungicides perform best when used preventively .

There are also successes in biological pest control. Bacteria and fungi can be used in the treatment of infections with Pythium aphanidermatum on lawns as well as in arable and greenhouse crops (flowers). The bacteria used include Bacillus subtilis , Candida oleophila , Enterobacter cloaceae and Pseudomonas species, the fungi Trichoderma species, namely Trichoderma harziamum , T. virens and T. hamatum .

meaning

The damage caused by Pythium aphanidermatum is difficult to determine because the host range is so wide and the infection leads to a wide variety of symptoms that are deleterious in different ways. The damage is significant and occurs primarily in warm, humid regions where the soil is partially wet. Valley areas and fields in floodplains are sometimes susceptible to infections. In general, the pathogen is important for crops such as corn , cotton , cereals and high quality garden plants. It is also economically important for crops grown in both greenhouses and soil-less culture media. Root infections and seedling rot are responsible for the decline in plant health and yield in commercially grown crops. Tomatoes are one of the most popular crops in the world and are grown in many regions. In tomatoes, P. aphanidermatum causes significant losses in nurseries where young, delicate seedlings are produced.

Individual evidence

  1. ↑ a b c d e f g h i j Pythium aphanidermatum . Retrieved April 27, 2019.
  2. ↑ a b c d e f g h i Oomycetes . Retrieved April 27, 2019.
  3. ↑ Pythium aphanidermatum (Edson) Fitzp. . In: GBIF Taxonomy Backbone . Global Biodiversity Information Facility . Retrieved July 11, 2019.
  4. ^ AG Norman (ed.): Soybean Physiology, Agronomy, and Utilization . Academic Press, 1987, ISBN 9780124335622 .
  5. ↑ a b c d Pythium root rot of Herbaceous Plants . Retrieved April 27, 2019.
  6. ↑ a b c d Pest, Disease and Weed Identification . Retrieved April 27, 2019.
  7. ↑ Clovis NB Koffi, Hortense A. Diallo, Justin Y. Koudio, Paula Kelly, Alan G. Buddie, Lukasz M. Tymo: Occurrence of Pythium aphanidermatum root and collar rot of Papaya (Carica papaya L.) in Cote d'Ivore . In: Fruit Vegetable and Cereal Science and Biotechnology . 4, No. special issue 1, March 2, 2010, pp. 62-67.
  8. ↑ TP Calvano, PJ Blatz, TJ Vento, BL Wickes, DA Sutton, EH Thompson, CE White, EM Renz, DR Hospenthal: Pythium aphanidermatum infection following combat trauma . In: J. Clin. Microbiol. . 49, No. 10, 2011, pp. 3710-3713. doi : 10.1128 / JCM.01209-11 .
  9. ↑ Pythium Damping-off, Root Rot and Stem Rot . Retrieved April 27, 2019.
  10. ↑ http://www.agf.gov.bc.ca/ornamentals/publications/pesticide/disease/damping_off.pdf
  11. ↑ Marcelo M. Zerillo, Bishwo N. Adhikari, John P. Hamilton, C. Robin Buell, C. André Lévesque, Ned Tisserat: Carbohydrate-Active Enzymes in Pythium and Their Role in Plant Cell Wall and Storage Polysaccharide Degradation . In: PLoS One . 8, No. 9, September 12, 2013, p. E72572. doi : 10.1371 / journal.pone.0072572 .
  12. ↑ H. Rachniyom, T. = Jaenaksorn: Effect of soluble silicon and Trichoderma harzianum on the in vitro growth of Pythium aphanidermatum . In: Journal of Agricultural Technology . 4, No. 2, 2008, pp. 57-71.
  13. ↑ Pythium root rots of Apiaceae and other vegetables . Retrieved April 27, 2019.
  14. ↑ a b UC IPM: UC Management Guidelines for Pythium Root Rot on Floriculture and Ornamental Nurseries . Agriculture and Natural Resources, University of California. March 2009. Retrieved April 27, 2019.
  15. ↑ Biswanath Das: Pythium Stalk Rot . Wheat Doctor. International Maize and Wheat Improvement Center, 2014.
  16. ↑ Christy E. Jeyaseelan, S. Tharmila, K. Niranjan: Antagonistic Activity of Trichoderma Spp. and Bacillus Spp. against Pythium Aphanidermatum Isolated from Tomato Damping off . In: Scholars Research Library 4.4 . 2012, pp. 1623-1627.

Web links