Jump to content

Phytophthora infestans: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
use classification of Phytophthora (which happens to also fix the taxobox color)
Jboltonnal (talk | contribs)
175 edits
Line 85: Line 85:
*[http://attra.ncat.org/attra-pub/lateblight.html Organic Alternatives for Late Blight Control in Potatoes, from ATTRA]
*[http://attra.ncat.org/attra-pub/lateblight.html Organic Alternatives for Late Blight Control in Potatoes, from ATTRA]
*[http://uspest.org/risk/tom_pot_map Google Map of Tomato Potato Blight Daily Risk across NE USA]
*[http://uspest.org/risk/tom_pot_map Google Map of Tomato Potato Blight Daily Risk across NE USA]
* [http://www.invasivespeciesinfo.gov/microbes/lateblight.shtml Species Profile- Late Blight (''Phytophthora infestans'')], National Invasive Species Information Center, [[United States National Agricultural Library]]. Lists general information and resources for Late Blight.


[[Category:Phytophthora|infestans]]
[[Category:Phytophthora|infestans]]

Revision as of 19:34, 16 February 2011

Phytophthora infestans
Symptom of blight on the potato leaf
Scientific classification
Domain:
Eukaryota
Kingdom:
Chromalveolata
Phylum:
Heterokontophyta
Class:
Oomycota
Order:
Peronosporales
Family:
Pythiaceae
Genus:
Phytophthora
Species:
P. infestans
Binomial name
Phytophthora infestans

Phytophthora infestans is an oomycete that causes the serious potato disease known as late blight or potato blight. (Early blight, caused by Alternaria solani, is also often called "potato blight"). Late blight was a major culprit in the 1840s European, the 1845 Irish and 1846 Highland potato famines. The organism can also infect tomatoes and some other members of the Solanaceae.[1]

Biology

The spores of this oomycete over-winter on infected tubers, particularly those that are left in the ground after the previous year's harvest, in cull piles, soil or infected volunteer plants and are spread rapidly in warm and wet conditions.[2] This can have devastating effects by destroying entire crops.

Spores develop on the leaves, spreading through the crop when temperatures are above 10 °C (50 °F) and humidity is over 75%-80% for 2 days or more. Rain can wash spores into the soil where they infect young tubers. Spores can also travel long distances on the wind.

The early stages of blight are easily missed, and not all plants are affected at once. Symptoms include the appearance of dark blotches on leaf tips and plant stems. White mould will appear under the leaves in humid conditions and the whole plant may quickly collapse. Infected tubers develop grey or dark patches that are reddish brown beneath the skin, and quickly decay to a foul-smelling mush caused by the infestation of secondary soft bacterial rots. Seemingly healthy tubers may rot later when in store.

Strains

Potatoes infected with late blight are shrunken on the outside, corky and rotted inside.

Until the 1970s, there was only one type of blight (A1) in the UK, and this was unable to produce resistant spores that could survive the winter. There are now two types (A1 and A2) which can mate and after that produce resistant spores, although the indications so far are that this rarely, if ever, happens in the UK. Mating can occur only between molds of different mating-types and is required for the production of resistant spores.

Genetics

In 2009 scientists completed the sequencing of the genome of P. infestans. It was found that the genome is considerably larger (240 Mb) compared to other Phytophthora species whose genomes have been sequenced; Phytophthora sojae has a 95 Mb genome and Phytophthora ramorum had a 65 Mb genome. It also contained a diverse variety of transposons and many gene families encoding for effector proteins that are involved in causing pathogenicity. These proteins are split into two main groups depending on whether they are produced by the water mold in the symplast (inside plant cells) or in the apoplast (between plant cells). Proteins produced in the symplast included RXLR proteins, which contain an arginine-X-leucine-arginine (where X can be any amino acid) sequence at the amino terminus of the protein. RXLR proteins are avirulence proteins, meaning that they can be detected by the plant and lead to a hypersensitive response, killing the oomycete. P. infestans was found to contain around 60% more of these proteins than other Phytophthora species and this may allow it to overcome host defences more quickly. Those found in the apoplast include hydrolytic enzymes such as proteases, lipases and glycosylases that act to degrade plant tissue, enzyme inhibitors to protect against host defence enzymes and necrotizing toxins. Overall the genome was found to have an extremely high repeat content (around 74%) and to have an unusual gene distribution in that some areas contain many genes whereas others contain very few.[3][1]

Management

P. infestans is still a difficult disease to control today by ordinary methods. There are many options in agriculture for the control of both damage to the foliage and infections of the tuber. Potatoes grow throughout the season, but it is estimated the tubers stop growing when 75% of the canopy has been destroyed.[4] Around the world the disease causes around $6 billion of damage to crops each year.[1]

Genetic engineering

Potatoes after exposure to Phytophthora infestans. The normal potatoes have blight but the cisgenic potatoes are healthy

In recent years, a resistance gene effective against all known strains of blight has been identified and successfully copied from a wild relative of the potato, Solanum bulbocastanum, and introduced into the genome of cultivated varieties of the potato.[5] This is an example of cisgenic genetic engineering.[6]

Sources of inoculum

Blight can be controlled by limiting the source of inoculum. Only good quality seed potatoes obtained from certified suppliers should be planted. Often discarded potatoes from the previous season and self-sown tubers can act as sources of inoculum.[7]

Environmental conditions

There are several environmental conditions that are conducive to P. infestans. During the 2009 growing season, which was colder than average, and with greater than average rainfall, there was a major infestation of tomato plants in the eastern United States.[8] By using weather forecasting systems, such as BLITECAST, if the following conditions occur as the canopy of the crop closes, then the use of fungicides is recommended to prevent an epidemic.[9]

  • A Beaumont Period is a period of 48 consecutive hours, in at least 46 of which the hourly readings of temperature and relative humidity at a given place have not been less than 20 °C (68 °F) and 75%, respectively.[10]
  • A Smith Period is at least two consecutive days where min temperature is 10 °C (50 °F) or above and on each day at least 11 hours when the relative humidity is greater than 90%.[11]

Potato varieties

Potato varieties vary in their susceptibility to blight. Most early varieties are very vulnerable; they should be planted early so that the crop matures before blight starts (usually in July). Many old crop varieties, such as King Edward potato are also very susceptible but are grown because they are wanted commercially. Maincrop varieties which are very slow to develop blight include Cara, Stirling, Teena, Torridon, Remarka and Romano. Some so-called resistant varieties can resist some strains of blight and not others, so their performance may vary depending on which are around. These crops have had polygenic resistance bred into them, and are known as "field resistant". New varieties such as Sarpo Mira and Sarpo Axona show great resistance to blight even in areas of heavy infestation. Defender is an American cultivar whose parentage includes Ranger Russet and Polish potatoes resistant to late blight. It is a long white-skinned cultivar with both foliar and tuber resistance to late blight. Defender was released in 2004.[12] These varieties are likely to gain great popularity as consumers increasingly embrace organically produced crops and reject food items that have been grown using fungicides and other chemicals. Researchers are currently working to develop a variety of potatoes that will be resistant both late and early blight. Researchers have found the wild potato species Solanum verrucosum to resist the late blight disease. They aim to make cultivated potatoes resistant to late blight by crossing the wild, resistant strain with the vulnerable, cultivated strain. In addition to this, researchers are crossing Solanum verrucosum with another wild potato species that is resistant to early blight, making a hybrid that is resistant to both late and early blight. They plan to cross the hybrid with cultivated potatoes to pass both resistant genes onto the cultivated species.[13]

Use of fungicides

Fungicides for the control of potato blight are normally only used in a preventative manner, perhaps in conjunction with disease forecasting. In susceptible varieties, sometimes fungicide applications may be needed weekly. An early spray is most effective. Metalaxyl is a fungicide that was marketed for use against P. infestans, but suffered serious resistance issues when used on its own. It is strongly advised to use metalaxyl along with carbamate compounds, or the especially effective synergistic Cymoxanil and Mancozeb combination as it is effective at managing metalaxyl resistant strains.[14]

In the past, copper sulfate solution (called 'bluestone') was used to combat potato blight. Copper pesticides remain in use in rare instances on organic crops.

Control of tuber blight

Ridging is often used to reduce tuber contamination by blight. This normally involves piling soil or mulch around the stems of the potato blight meaning the pathogen has farther to travel to get to the tuber.[15]

The canopy can also be destroyed around 5 weeks before harvest. This can be done via a contact herbicide or using sulfuric acid to burn off the foliage.

Historical impact

The effects of Phytophthora infestans in Ireland in 1845-57 were one of the factors which caused over one million to starve to death and forced another two million to emigrate from affected countries. Most commonly referenced is the Great Irish Famine, during the late 1840s.

The origin of Phytophthora infestans can be traced to a valley in the highlands of central Mexico. The first recorded instances of the disease were in the United States, in Philadelphia and New York City in early 1843. Winds then spread the spores, and in 1845 it was found from Illinois to Nova Scotia, and from Virginia to Ontario. It crossed the Atlantic Ocean with a shipment of seed potatoes for Belgian farmers in 1845.[16]

Use as a biological weapon

Potato blight was one of more than 17 agents that the United States researched as potential biological weapons before the nation suspended its biological weapons program.[17] France, Canada, USA and the Soviet Union also researched P. infestans as a biological weapon in the 1940s and 50s.[18]

References

  1. ^ a b c Chand, Sudeep (9 September 2009), Killer genes cause potato famine, BBC News, retrieved 2009-09-26
  2. ^ Koepsell, Paul A.; Pscheidt, Jay W. (1994), 1994 Pacific Northwest Plant Disease Control Handbook, Corvallis: Oregon State University Press, p. 165
  3. ^ Haas, Brian (17 September 2009), "Genome sequence and analysis of the Irish potato famine pathogen Phytophthora infestans", Nature, 461 (7262): 393–398, doi:10.1038/nature08358, PMID 19741609 {{citation}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  4. ^ James, W. C. (1974), "Assessment of Plant Diseases and Losses", Annual Review of Phytopathology, 12 (1): 27–48, doi:10.1146/annurev.py.12.090174.000331
  5. ^ Song, Junqi; Bradeen, James M.; Naess, S. Kristine; Raasch, John A.; Wielgus, Susan M.; Haberlach, Geraldine T.; Liu, Jia; Kuang, Hanhui; Austin-Phillips, Sandra (2003), "Gene RB cloned from Solanum bulbocastanum confers broad spectrum resistance to potato late blight", PNAS, 100 (16): 9128–9133, doi:10.1073/pnas.1533501100, PMC 170883, PMID 12872003 {{citation}}: More than one of |first1= and |first= specified (help); More than one of |last1= and |last= specified (help)
  6. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1007/s11540-008-9097-y, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1007/s11540-008-9097-y instead. Free version
  7. ^ Zwankhuizen, Maarten J.; Govers, Francine; Zadoks, Jan C. (1998), "Development of potato late blight epidemics: Disease foci, disease gradients, and infection sources", Phytopathology, 88 (8): 754–763, doi:10.1094/PHYTO.1998.88.8.754, PMID 18944880
  8. ^ Moskin, Julia (July 17, 2009), "Outbreak of Fungus Threatens Tomato Crop", The New York Times
  9. ^ MacKenzie, D. R. (1981), "Scheduling fungicide applications for potato late blight with Blitecast", Plant Disease, 65: 394–399, doi:10.1094/PD-65-394
  10. ^ Beaumont period
  11. ^ http://www.potatocrop.com/blight/blightaboutsmith.asp [dead link]
  12. ^ Novy, R. G.; Love, S. L. (2006)), "Defender : A high-yielding, processing potato cultivar with foliar and tuber resistance to late blight", American Journal of Potato Research, 83 (1): 9–19, doi:10.1007/BF02869605 {{citation}}: Check date values in: |year= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  13. ^ "Wild Potato Germplasm Holds Key to Disease Resistance". USDA Agricultural Research Service. June 16 2010. {{cite web}}: Check date values in: |date= (help)
  14. ^ Mukerji, K. G. (2004), Fruit and Vegetable Diseases, Boston: Kluwer Academic Publishers, p. 196, ISBN 1402019769
  15. ^ Glass, J. R.; Johnson, K. B.; Powelson, M. L. (2001), "Assessment of Barriers to Prevent the Development of Potato Tuber Blight", Plant Disease, 85 (5): 521–528, doi:10.1094/PDIS.2001.85.5.521
  16. ^ Reader, John (March 17, 2008), "The Fungus That Conquered Europe", New York Times, retrieved 2008-03-18
  17. ^ "Chemical and Biological Weapons: Possession and Programs Past and Present", James Martin Center for Nonproliferation Studies, Middlebury College, April 9, 2002, accessed November 14, 2008.
  18. ^ Suffert, Frédéric; Latxague, Émilie; Sache, Ivan (2009), "Plant pathogens as agroterrorist weapons: assessment of the threat for European agriculture and forestry", Food Security, 1 (2): 221–232, doi:10.1007/s12571-009-0014-2

Further reading

  • Erwin, Donald C.; Ribeiro, Olaf K. (1996), Phytophthora Diseases Worldwide, St. Paul, MN: American Phytopathological Society Press, ISBN 0890542120
  • Lucas, J. A.; Shattock, R. C.; Shaw, D. S.; Cooke, Louise, eds. (1991), Phytophthora, British Mycological Society Symposia, Cambridge: Cambridge University Press, ISBN 0521400805
  • Govers, Francine; Gijzens, Mark (2006), "Phytophthora Genomics: The Plant-Destroyer's Genome Decoded", Molecular Plant-Microbe Interactions, 19 (12): 1295–1301, doi:10.1094/MPMI-19-1295, PMID 17153913
Wikimedia Commons has media related to Phytophthora infestans.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Phytophthora_infestans&oldid=414293240"