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
Life Cycle 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).
Cell Structure 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).
Metabolism 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).
Describe the size and content of the genome. How many chromosomes? Other interesting features? What is known about its sequence?
Ecology and Pathogenesis
Habitat; symbiosis; environmental or industrial relevance; contributions to environment.
If relevant, how does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as host symptoms.
[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 .