Difference between revisions of "(CPOK)-Phytophthora infestans"
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==Ecology and Pathogenesis==
==Ecology and Pathogenesis==
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Revision as of 04:11, 18 December 2019
Genus species: Phytopthora
Alternate name(s) of this species: Phytophthora blight
Description and Significance
Phytophthora infestans (P.infestans) are oomycete plant pathogens that acts as obligate parasites to potato and tomato plants causing Late Blight Disease. They can affect other members of the Solanaceae family such as nightstands, and tomatillos (4). P.infestans are similar to fungi as they grow as mycelium and produce spores that can be aerially dispersed Its popularity is due to being the major culprit for the 1845 Great Irish Famine and 1846 Highland Potato Famine (2). Its importance is seen significantly in biosecurity, as it poses a serious threat to the potato and tomato industry.
Life Cycle, Cell Structure, Metabolism
In the asexual life cycle, sporangia are produced on sporangiophores. When the temperature is greater than 15 degrees celsius, the sporangia can be aerially dispersed to allow direct germination to occur. The spores then infect plants, and is followed by the formation of a germ tube to retrieve nutrients from the host (2). When temperatures are below 15 degrees celsius, indirect germination will occur. In this case, sporangia are aerially dispersed, land on plant tissue, and release zoospores. In the sexual life cycle, hormonal communication initiates the sexual spores oospores to form. When compatible mating types are present, Karyogamy takes place in which the antheridium and oogonium nuclei fuse. This leads to the formation of the diploid oospore that will become a sporangium, and then the cycle continues as it would asexually (4).
In the primary dispersal stages, sporangia are multinucleate and zoospores are uninucleate. When infection occurs, zoospores will discard flagella and synthesize a cell wall to form a cyst. When germination occurs, the cysts enter the host tissue forming a swollen germ tube. From there, Hyphae emerge from the primary infection vesicle and haustoria structures emerge into host cells (3).
Haustoria structures penetrate the mesophyll cells and act as feeding structures to obtain nutrients for growth such as organic carbon sources, essential major element (such as O, H, P, N, S, K, Ca, Mg, Fe), trace elements, and Thiamine (2).
The P. infestans are diploid, have 8-10 chromosomes, and is made up of approximately 240 megabases (Mb). This makes them the largest and most complex genome in the chromalveolates. This is due to its proliferation of repetitive DNA comprising 74% of its genome and a high 52% G-C content (1).
Ecology and Pathogenesis
Temperature is a determinant of how rapidly Late Blight Disease can spread. P. infestans are found in moist and cool weather environments, and warmer temperatures give rise to higher lesion growth rates. The pathogen’s sporangia and sporangiophores can be seen on the lower foliage surface of potato and tomato leaves and stems. The symptoms of the pathogen include dark blotches on leaf tips and stems, dark patches on tubers, and dark maroon patches inside the plant’s skin. The persistence of the pathogen is attributed to environmental factors such as moisture, soil, and pH. To control the growth of P. infestans there exists biocontrol efforts such as Lysobacter strains. These strains produce extracellular enzymes that have been known to be used as biological agents for plant diseases (4). However, the effectiveness of Lysobacter can be altered with temperature, as the temperature can contribute to the physiological characteristics of the Lysobacter strains and the microbial communities that reside within the blight disease infected plants. P. infestans is a concerning problem in agriculture as it the most destructive disease of potato, contributing to an annual worldwide crop loss of $6.7 billion USD.
[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.
Page authored by Chansorena Pok, student of Dr. Marc Orbach, University of Arizona .