Phytophthora infestans

{{Speciesbox

| image = Late_blight_on_potato_leaf_2.jpg

| image_alt = Symptom of late blight on the underside of a potato leaf

| image_caption = Symptom of late blight on the underside of a potato leaf

| genus = Phytophthora

| species = infestans

| authority = (Mont.) de Bary

| synonyms =

| subdivision_ranks =

| subdivision =

}}

Phytophthora infestans is an oomycete or water mold, a fungus-like microorganism that causes the serious potato and tomato 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 1845–1852 Irish, and the 1846 Highland potato famines. The organism can also infect some other members of the Solanaceae.{{Citation|url=http://news.bbc.co.uk/1/hi/sci/tech/8246944.stm|title=Killer genes cause potato famine |last=Chand|first=Sudeep |date=9 September 2009|publisher=BBC News|access-date=26 September 2009}}{{Citation|title=Potato and tomato late blight caused by Phytophthora infestans: An overview of pathology and resistance breeding |last=Nowicki|first=Marcin|date=17 August 2011|doi= 10.1094/PDIS-05-11-0458|pmid=30731850|display-authors=etal|volume=96|issue=1|journal=Plant Disease|pages=4–17|doi-access=}}{{Citation |last=Nowicki|first=Marcin |chapter= Late Blight of Tomato|title=Translational Genomics for Crop Breeding|date=11 October 2013|doi=10.1002/9781118728475.ch13|display-authors=etal |pages=241–65|isbn=978-1-118-72847-5|s2cid=83142160 }} The pathogen is favored by moist, cool environments: sporulation is optimal at {{convert|12–18|C|F|0}} in water-saturated or nearly saturated environments, and zoospore production is favored at temperatures below {{convert|15|C|F|0}}. Lesion growth rates are typically optimal at a slightly warmer temperature range of {{convert|20 to 24|C|F|0}}.{{Citation |last1=Haverkort |first1=A. J. |last2=Struik |first2=P. C. |last3=Visser |first3=R. G. F.|last4=Jacobsen |first4= E |year=2009 |title=Applied biotechnology to combat late blight in potato caused by Phytophthora infestans|journal=Potato Research|volume=52 |issue=3 |pages=249–64 |doi= 10.1007/s11540-009-9136-3|s2cid=2850128 |url=http://library.wur.nl/WebQuery/wurpubs/381896 |type=Submitted manuscript }}

Etymology

The genus name Phytophthora comes from the Greek {{lang|el|φυτό}} ({{transliteration|el|phyto}}), meaning "plant" – plus the Greek {{lang|el|φθορά}} ({{transliteration|el|phthora}}), meaning "decay, ruin, perish".{{source needed|reason=Unlikely that modern Greek φυτό instead of ancient Greek φυτόν is intended.|date=April 2025}} The species name infestans is the present participle of the Latin verb {{lang|la|infestare}}, meaning "attacking, destroying", from which the word "to infest" is derived. The name Phytophthora infestans was coined in 1876 by the German mycologist Heinrich Anton de Bary (1831–1888).{{cite journal |last1=Bary |first1=A. de |title=Researches into the nature of the potato fungus Phytophthora infestans |journal=Journal of the Royal Society of Agriculture of England|date=1876 |volume=12 |pages=239–269 |url=https://books.google.com/books?id=jZkEAAAAYAAJ&pg=RA1-PA239 |series=2nd series}}{{Cite web|url=https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?lvl=0&id=4787|title=Taxonomy browser (Phytophthora infestans)|website=www.ncbi.nlm.nih.gov}}

Life cycle, signs and symptoms

Image:Tomato with Phytophthora infestans (late blight).jpg]]

Image:Tomato late blight stem lesion 3 (5816739322).jpg plant]]

Image:Tomato late blight fruit cluster (5816739612).jpges]]

Image:Phytophtora infestans-effects.jpg|alt=Infected potatoes are shrunken on the outside, and corky as well as rotted on the inside.]]

File:07 08 life cycle, Phytophthora infestans on potato, Peronosporales, Oomycota (M. Piepenbring).png on potato|293x293px]]

The asexual life cycle of Phytophthora infestans is characterized by alternating phases of hyphal growth, sporulation, sporangia germination (either through zoospore release or direct germination, i.e. germ tube emergence from the sporangium), and the re-establishment of hyphal growth.{{Citation|title=A simple dual stain for detailed investigations of plant-fungal pathogen interactions|last=Nowicki|first=Marcin|date=15 May 2013|doi= 10.2478/v10032-012-0016-z|display-authors=etal|volume=77|pages=61–74|journal=Vegetable Crops Research Bulletin|doi-access=free}} There is also a sexual cycle, which occurs when isolates of opposite mating type (A1 and A2, see {{Slink||Mating types}} below) meet. Hormonal communication triggers the formation of the sexual spores, called oospores.Judelson HS, Blanco FA (2005) The spores of Phytophthora: weapons of the plant destroyer. Nature Microbiology Reviews 3: 47–58. The different types of spores play major roles in the dissemination and survival of P. infestans. Sporangia are spread by wind or water and enable the movement of P. infestans between different host plants. The zoospores released from sporangia are biflagellated and chemotactic, allowing further movement of P. infestans on water films found on leaves or soils. Both sporangia and zoospores are short-lived, in contrast to oospores which can persist in a viable form for many years.

People can observe P. infestans produce dark green, then brown then black spots on the surface of potato leaves and stems, often near the tips or edges, where water or dew collects.{{Cite web |date=May 2017 |title=Late Blight in Potato |url=https://www.ag.ndsu.edu/publications/crops/late-blight-in-potato |access-date=2021-11-30 |website=North Dakota State University Agriculture Department}} The sporangia and sporangiophores appear white on the lower surface of the foliage. As for tuber blight, the white mycelium often shows on the tubers' surface.{{Citation |last1=Fry |first1=W. E. |last2=Grünwald |first2=N. J. |year=2010|title=Introduction to Oomycetes|journal=The Plant Health Instructor |doi=10.1094/PHI-I-2010-1207-01}}

Under ideal conditions, P. infestans completes its life cycle on potato or tomato foliage in about five days. Sporangia develop on the leaves, spreading through the crop when temperatures are above {{convert|10|°C|°F}} and humidity is over 75–80% for 2 days or more. Rain can wash spores into the soil where they infect young tubers, and the spores can also travel long distances on the wind. The early stages of blight are easily missed. Symptoms include the appearance of dark blotches on leaf tips and plant stems. White mold 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.

P. infestans survives poorly in nature apart from on its plant hosts. Under most conditions, the hyphae and asexual sporangia can survive for only brief periods in plant debris or soil, and are generally killed off during frosts or very warm weather. The exceptions involve oospores, and hyphae present within tubers. The persistence of viable pathogen within tubers, such as those that are left in the ground after the previous year's harvest or left in cull piles is a major problem in disease management. In particular, volunteer plants sprouting from infected tubers are thought to be a major source of inoculum (or propagules) at the start of a growing season.{{citation |last1=Koepsell |first1=Paul A. |last2=Pscheidt |first2=Jay W. |title=1994 Pacific Northwest Plant Disease Control Handbook |year=1994|publisher=Oregon State University Press|location=Corvallis |page=165 }} This can have devastating effects by destroying entire crops.

=Mating types=

The mating types are broadly divided into A1 and A2.{{cite journal | last=Judelson | first=Howard S. | title=Metabolic Diversity and Novelties in the Oomycetes | journal=Annual Review of Microbiology | volume=71 | issue=1 | date=2017-09-08 | issn=0066-4227 | doi=10.1146/annurev-micro-090816-093609 | pages=21–39| pmid=28504899 }} Until the 1980s populations could only be distinguished by virulence assays and mating types, but since then more detailed analysis has shown that mating type and genotype are substantially decoupled. These types each produce a mating hormone of their own. Pathogen populations are grouped into clonal lineages of these mating types and includes:

==A1==

A1 produces a mating hormone, a diterpene α1. Clonal lineages of A1 include:

{{ Visible anchor |CN-1|CN-2|CN-4|CN-5|CN-6|CN-7|CN-8}}CN-1, -2, -4, -5, -6, -7, -8 – mtDNA haplotype Ia, China in 1996–97{{cite journal|last1=Guha Roy | first1=Sanjoy |last2=Dey |first2=Tanmoy |last3=Cooke |first3=David E. L. |last4=Cooke |first4=Louise R. | title=The dynamics of Phytophthora infestans populations in the major potato-growing regions of Asia | journal=Plant Pathology| volume=70 | issue=5 | date=2021-02-27 | issn=0032-0862 | doi=10.1111/ppa.13360 | pages=1015–1031|bibcode=2021PPath..70.1015G | s2cid=233882518}}
{{ Visible anchor |CN-3}} – Ia, China, 1996–97
{{ Visible anchor |CN-10}} – Ia, China, 2004
{{ Visible anchor |CN-11}} – IIb, China, 2000 & 2002
{{ Visible anchor |CN01}} – IIa, China, 2004–09
{{ Visible anchor |CN03}} – Ia/IIb, China, 2004–09
{{ Visible anchor |FAM-1}} – (only presumed to be A1), mtDNA haplo Ia subtype {{ Visible anchor |HERB-1}}, Japan, Philippines, India, China, Malaysia, Nepal, present some time before 1950
{{ Visible anchor |IN-1}} – Ia, India, Nepal, 1993
{{ Visible anchor |IN-2}} – Ia, India, 1993
{{ Visible anchor |JP-2|SIB-1|RF006}}JP-2/SIB-1/RF006 – mtDNA haplo IIa, distinguishable by RG57, intermediate level of metalaxyl resistance, Japan, China, Korea, Thailand, 1996–present
{{ Visible anchor |JP-3}} – IIa, distinguishable by RG57, intermediate level of metalaxyl resistance, Japan, 1996–present
{{ Visible anchor |JP-4}} – IIa, distinguishable by RG57, intermediate level of metalaxyl resistance, Japan, 1996–present
{{ Visible anchor |KR-1 Zhang}} sensu Zhang (not to be confused with #KR-1 sensu Gotoh below) – IIa, Korea, 2002–04
{{ Visible anchor |KR_1_A1}}KR_1_A1 – mtDNA haplo unknown, Korea, 2009–16
{{ Visible anchor |MO-6}} – Ia, China, 2004
{{ Visible anchor |NP-1}} – Ia, India, Nepal, 1993, 1996–97
{{ Visible anchor |NP-2}} – Ia, Nepal, 1997
{{ Visible anchor |NP1}} – Ia, Nepal, 1999–2000
{{ Visible anchor |NP2 A1}} – (Also A2, see #the A2 type of NP2 below) Ia, Nepal, 1999–2000
{{ Visible anchor |NP3|NP3/US-1}} (not to be confused with #US-1 below) – Ib, Nepal, 1999–2000
{{ Visible anchor |US-1}} (not to be confused with #NP3/US-1 above) – Ib, China, India, Nepal, Japan, Taiwan, Thailand, Vietnam, 1940–2000
{{ Visible anchor |NP4|NP5|NP7|NP9|text=NP4, 5, 7, and 9}} – Ia, Nepal, 1999–2000
{{ Visible anchor |NP6}} – mtDNA haplo unknown, Nepal, 1999–2000
{{ Visible anchor |US-11}} – IIb, Taiwan, Korea, Vietnam, 1998–2016
{{ Visible anchor |US-16}} – IIb, China, 2002 & 2004
{{ Visible anchor |US-17}} – IIa, Korea, 2003–04
{{ Visible anchor |US-23}}
{{ Visible anchor |US-24}}
{{ Visible anchor |2_A1}} – Ia, Indonesia, 2016–19
{{ Visible anchor |T30-4}}

==A2==

Discovered by John Niederhauser in the 1950s, in the Toluca Valley in Central Mexico, while working for the Rockefeller Foundation's Mexican Agriculture Program. Published in Niederhauser 1956. A2 produces a mating hormone α2. Clonal lineages of A2 include:

CN02 – See #13_A2/CN02 below
{{ Visible anchor |US-22}} – with mtDNA haplotype H-20
{{ Visible anchor |JP-1}} – IIa, Japan, Korea, Indonesia, late 1980s–present
{{ Visible anchor |KR-1 Gotoh}} sensu Gotoh (not to be confused with #KR-1 sensu Zhang above) – IIa, differs from JP-1 by one RG57 band, Korea, 1992
{{ Visible anchor |KR_2_A2}} – mtDNA haplo unknown, Korea, 2009–16
{{ Visible anchor |CN-9}} – Ia, China, 2001
{{ Visible anchor |NP2 A2}} – (Also A1, see #the A1 type of NP2 above) Ia, Nepal, 1999–2000
{{ Visible anchor |NP8}} – Ib, Nepal, 1999–2000
{{ Visible anchor |NP10|NP11|text=NP10 & 11}} – Ia, Nepal, 1999–2000
{{ Visible anchor |TH-1}} – Ia, Thailand, China, Nepal, 1994 & 1997
Unknown – Ib, India, 1996–2003
{{ Visible anchor |BR-1}} – Brazil
{{ Visible anchor |US-7}}
{{ Visible anchor |US-8}}
{{ Visible anchor |US-14}} – IIa, Korea, 2002–03
{{ Visible anchor |13_A2|CN02}}{{cite journal |last1=Cooke |first1=David E. L. |last2=Cano |first2=Liliana M. |last3=Raffaele |first3=Sylvain |last4=Bain |first4=Ruairidh A. |last5=Cooke |first5=Louise R. |last6=Etherington |first6=Graham J. |last7=Deahl |first7=Kenneth L. |last8=Farrer |first8=Rhys A. |last9=Gilroy |first9=Eleanor M. |last10=Goss |first10=Erica M. |last11=Grünwald |first11=Niklaus J. |last12=Hein |first12=Ingo |last13=MacLean |first13=Daniel |last14=McNicol |first14=James W. |last15=Randall |first15=Eva |last16=Oliva |first16=Ricardo F. |last17=Pel |first17=Mathieu A. |last18=Shaw |first18=David S. |last19=Squires |first19=Julie N. |last20=Taylor |first20=Moray C. |last21=Vleeshouwers |first21=Vivianne G. A. A. |last22=Birch |first22=Paul R. J. |last23=Lees |first23=Alison K. |last24=Kamoun |first24=Sophien |title=Genome Analyses of an Aggressive and Invasive Lineage of the Irish Potato Famine Pathogen|journal=PLOS Pathogens|date=4 October 2012 |volume=8 |issue=10 |page=e1002940 |doi=10.1371/journal.ppat.1002940|pmid=23055926 |pmc=3464212 |doi-access=free }}{{cite journal | last=Fry | first=William E. | title=Phytophthora infestans: New Tools (and Old Ones) Lead to New Understanding and Precision Management | journal=Annual Review of Phytopathology | volume=54 | issue=1 | date=2016-08-04 | issn=0066-4286 | doi=10.1146/annurev-phyto-080615-095951 | pages=529–547| pmid=27359366 | doi-access=free | bibcode=2016AnRvP..54..529F }}/CN02 – Ia, China, India, Bangladesh, Nepal, Pakistan, Myanmar, 2005–19

==Self-fertile==

A self-fertile type was present in China between 2009 and 2013.

Physiology

{{Vanchor|PiINF1|text=PiINF1}} is the {{Vanchor|INF1|text=INF1}} in P. infestans. Hosts respond with autophagy upon detection of this elicitor, Liu et al. 2005 finding this to be the only alternative to mass hypersensitivity leading to mass programmed cell death.{{cite journal | last1=Yang | first1=Meng | last2=Ismayil | first2=Asigul | last3=Liu | first3=Yule | title=Autophagy in Plant-Virus Interactions | journal=Annual Review of Virology | volume=7 | issue=1 | date=2020-09-29 | issn=2327-056X | doi=10.1146/annurev-virology-010220-054709 | pages=403–419| pmid=32530794 | s2cid=219621432 }}

Genetics

P. infestans is diploid, with about 8–10 chromosomes, and in 2009 scientists completed the sequencing of its genome. The genome was found to be considerably larger (240 Mbp) than that of most other Phytophthora species whose genomes have been sequenced; P. sojae has a 95 Mbp genome and P. ramorum had a 65 Mbp genome. About 18,000 genes were detected within the P. infestans 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. Some RXLR proteins are avirulence proteins, meaning that they can be detected by the plant and lead to a hypersensitive response which restricts the growth of the pathogen. P. infestans was found to encode around 60% more of these proteins than most other Phytophthora species. 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.{{cite journal|year=2009|doi-access=free|journal=Nature|issn=0028-0836|volume=461|issue=7262|last1=Haas|first1=Brian J.|last2=Kamoun|first2=Sophien|author2-link=Sophien Kamoun|last3=Zody|first3=Michael|last4=Jiang|first4=Rays|last5=Handsaker|first5=Robert|last6=Cano|first6=Liliana|last7=Grabherr|first7=Manfred|last8=Kodira|first8=Chinnappa|last9=Raffaele|first9=Sylvain|last10=Torto-Alalibo|first10=Trudy|last11=Bozkurt|first11=Tolga|last12=Ah-Fong|first12=Audrey|last13=Alvarado|first13=Lucia|last14=Anderson|first14=Vicky|last15=Armstrong|first15=Miles|last16=Avrova|first16=Anna|last17=Baxter|first17=Laura|last18=Beynon|first18=Jim|last19=Boevink|first19=Petra|last20=Bollmann|first20=Stephanie|last21=Bos|first21=Jorunn|last22=Bulone|first22=Vincent|last23=Cai|first23=Guohong|last24=Cakir|first24=Cahid|last25=Carrington|first25=James|last26=Chawner|first26=Megan|last27=Conti|first27=Lucio|last28=Costanzo|first28=Stefano|last29=Ewan|first29=Richard|last30=Fahlgren|first30=Noah|last31=Fischbach|first31=Michael|last32=Fugelstad|first32=Johanna|last33=Gilroy|first33=Eleanor|last34=Gnerre|first34=Sante|last35=Green|first35=Pamela|last36=Grenville-Briggs|first36=Laura|last37=Griffith|first37=John|last38=Grünwald|first38=Niklaus|last39=Horn|first39=Karolyn|last40=Horner|first40=Neil|last41=Hu|first41=Chia-Hui|last42=Huitema|first42=Edgar|last43=Jeong|first43=Dong-Hoon|last44=Jones|first44=Alexandra|last45=Jones|first45=Jonathan|last46=Jones|first46=Richard|last47=Karlsson|first47=Elinor|last48=Kunjeti|first48=Sridhara|last49=Lamour|first49=Kurt|last50=Liu|first50=Zhenyu|last51=Ma|first51=LiJun|last52=MacLean|first52=Daniel|last53=Chibucos|first53=Marcus|last54=McDonald|first54=Hayes|last55=McWalters|first55=Jessica|last56=Meijer|first56=Harold|last57=Morgan|first57=William|last58=Morris|first58=Paul|last59=Munro|first59=Carol|last60=O'Neill|first60=Keith|last61=Ospina-Giraldo|first61=Manuel|last62=Pinzón|first62=Andrés|last63=Pritchard|first63=Leighton|last64=Ramsahoye|first64=Bernard|last65=Ren|first65=Qinghu|last66=Restrepo|first66=Silvia|author-link66=Silvia Restrepo|last67=Roy|first67=Sourav|last68=Sadanandom|first68=Ari|last69=Savidor|first69=Alon|last70=Schornack|first70=Sebastian|last71=Schwartz|first71=David|last72=Schumann|first72=Ulrike|last73=Schwessinger|first73=Ben|last74=Seyer|first74=Lauren|last75=Sharpe|first75=Ted|last76=Silvar|first76=Cristina|last77=Song|first77=Jing|last78=Studholme|first78=David|last79=Sykes|first79=Sean|last80=Thines|first80=Marco|last81=van de Vondervoort|first81=Peter|last82=Phuntumart|first82=Vipaporn|last83=Wawra|first83=Stephan|last84=Weide|first84=Rob|last85=Win|first85=Joe|last86=Young|first86=Carolyn|last87=Zhou|first87=Shiguo|last88=Fry|first88=William|last89=Meyers|first89=Blake|last90=van West|first90=Pieter|last91=Ristaino|first91=Jean|last92=Govers|first92=Francine|last93=Birch|first93=Paul|last94=Whisson|first94=Stephen|last95=Judelson|first95=Howard|last96=Nusbaum|first96=Chad|pages=393–398|title=Genome sequence and analysis of the Irish potato famine pathogen Phytophthora infestans|doi=10.1038/nature08358|pmid=19741609|url=https://wrap.warwick.ac.uk/62453/1/WRAP_Jones_nature08358.pdf|bibcode=2009Natur.461..393H|s2cid=4385549}}

The pathogen shows high allelic diversity in many isolates collected in Europe. This may be due to widespread trisomy or polyploidy in those populations.

{{ Cite book

| language = en

| year = 2013

| number = 2

| pages = xi+244

| title = Phytophthora: A Global Perspective

| last = Lamour

| first = Kurt

| isbn = 978-1-78064-093-8

| publisher = Centre for Agriculture and Bioscience International

| series = CABI Plant Protection Series

| lccn = 2012042152

}}

Research

Study of P. infestans presents sampling difficulties in the United States.{{ RP |page=43}} It occurs only sporadically and usually has significant founder effects due to each epidemic starting from introduction of a single genotype.{{ RP |page=43}}

Origin and diversity

File:Modell eines Querschnitts durch ein Kartoffelblatt mit Phytophthora infestans (Kartoffelpilz) -Osterloh Nr. 55- -Brendel 10 k, 1- (2).jpg]]

The highlands of central Mexico were considered to be the center of origin of P. infestans, although others have proposed its origin to be in the Andes, which is also the origin of potatoes.{{cite journal | last1 = Gomez-Alpizar | first1 = L | last2 = Carbone | first2 = I | last3 = Ristaino | first3 = JB | year = 2007 | title = An Andean origin of Phytophthora infestans inferred from mitochondrial and nuclear gene genealogies | journal= Proceedings of the National Academy of Sciences | volume = 104 | issue = 9| pages = 3306–11 | doi=10.1073/pnas.0611479104 | pmid=17360643 | pmc=1805513| bibcode = 2007PNAS..104.3306G | doi-access = free }}{{Cite journal | doi = 10.1146/annurev.phyto.43.040204.135906| pmid = 16078881| title = The Biology of Phytophthora infestans at Its Center of Origin| journal = Annual Review of Phytopathology| volume = 43| pages = 171–90| year = 2005| last1 = Grünwald | first1 = N. J. | last2 = Flier | first2 = W. G. | issue = 1| bibcode = 2005AnRvP..43..171G}} A study published in 2014 evaluated these two alternate hypotheses and found conclusive support for central Mexico being the center of origin.{{Cite journal | doi = 10.1073/pnas.1401884111| title = The Irish potato famine pathogen Phytophthora infestans originated in central Mexico rather than the Andes| journal = Proceedings of the National Academy of Sciences| year = 2014| last1 = Goss | first1 = E. M.| last2 = Tabima | first2 = J. F.| last3 = Cooke | first3 = D. E. L.| last4 = Restrepo | first4 = S.| last5 = Fry | first5 = W. E.| last6 = Forbes | first6 = G. A.| last7 = Fieland | first7 = V. J.| last8 = Cardenas | first8 = M.| last9 = Grünwald | first9 = N. J. | volume=111 | issue = 24| pages=8791–96 | pmid=24889615 | pmc=4066499

| bibcode = 2014PNAS..111.8791G| doi-access = free}} However, their study did not include either an extensive global sampling of P. infestans or historic genomes. Support for a Mexican origin {{endash}} specifically the Toluca Valley{{cite book|year=2015|location=St. Paul, Minnesota, US|first=Michael|title=Population Biology of Plant Pathogens : Genetics, Ecology, and Evolution|publisher=APS Press/The American Phytopathological Society|last=Milgroom|isbn=978-0-89054-450-1|lccn=2014943809}} {{endash}} came from multiple observations including the fact that populations are genetically most diverse in Mexico, late blight is observed in native tuber-bearing Solanum species, populations of the pathogen are in Hardy–Weinberg equilibrium, the two mating (see § Mating types above) types occur in a 1:1 ratio, and detailed phylogeographic and evolutionary studies.{{Cite journal |last1=Ristaino |first1=J. B. |year=2002 |title=Tracking historic migrations of the Irish potato famine pathogen, Phytophthora infestans. |journal=[Microbes and Infection] |volume=4 |issue=13 |pages=1369–77 |doi= 10.1016/S1286-4579(02)00010-2|pmid= 12443902|doi-access=}}{{Cite journal |last1=Martin |first1=M. D. |last2=Vieira FG |first2=F. G. |last3=Ho |first3=S.Y. |last4=Wales |first4=N. |last5=Schubert M, Seguin-Orlando A |first5=M. |last6=Seguin-Orlando |first6=A. |last7=Ristaino |first7=J. B. |last8=Gilbert |first8=T |year=2015 |title=Genomic characterization of a South American Phytophthora hybrid mandates reassessment of the geographic origins of Phytophthora infestans. |url=https://doi:10.1093/molbev/msv241 |journal=[Molecular Biology and Evolution] |volume=33 |issue=2 |pages=478–491 |doi=10.1093/molbev/msv241 |pmid= 26576850|doi-access=|pmc=4866541 }}{{Cite journal |last1=Coomber |first1=A |last2=Saville |first2=A. |last3=Martin |first3=M. |last4=Carbone |first4=I. |last5=Ristaino |first5=J. |date=2024 |title=A Pangenome Analysis Reveals Center of Origin and Evolutionary History of the Phytophthora Ic Clade. |journal=PLOS One |volume=20 |issue=1 |pages=e0314509 |doi=10.1371/journal.pone.0314509|doi-access=free |pmid=39854309 |pmc=11760636 }}{{Cite journal | doi = 10.1094/PHYTO.1997.87.4.375| pmid = 18945115| title = Population genetic structure of Phytophthora infestans in Ecuador|journal=Phytopathology | volume = 87| issue = 4| pages = 375–80| year = 1997| last1 = Forbes | first1 = G. A. | last2 = Escobar | first2 = X. C. | last3 = Ayala | first3 = C. C. | last4 = Revelo | first4 = J. | last5 = Ordoñez | first5 = M. E. | last6 = Fry | first6 = B. A. | last7 = Doucett | first7 = K. | last8 = Fry | first8 = W. E. | doi-access = | bibcode = 1997PhPat..87..375F}}{{Cite journal | doi = 10.1111/j.1365-3059.1991.tb02400.x| title = A second world-wide migration and population displacement of Phytophthora infestans?|journal=Plant Pathology| volume = 40| issue = 3| pages = 422–30| year = 1991| last1 = Spielman | first1 = L. J. | last2 = Drenth | first2 = A.| last3 = Davidse | first3 = L. C.| last4 = Sujkowski | first4 = L. J.| last5 = Gu | first5 = W.| last6 = Tooley | first6 = P. W.| last7 = Fry | first7 = W. E.| bibcode = 1991PPath..40..422S}} For instance, while sexual recombination is regarded as evidence for a Mexican origin, P. infestans is mostly asexual and does not widely engage in sexual reproduction, despite the migration of the A2 mating type into Europe. Furthermore, the sister lineages of P. infestans, namely P. mirabilis and P. ipomoeae are endemic to central Mexico.{{Cite journal | doi = 10.1017/S0953756202006123| title = Phytophthora ipomoeae sp. nov., a new homothallic species causing leaf blight on Ipomoea longipedunculata in the Toluca Valley of central Mexico| journal = Mycological Research| volume = 106| issue = 7| pages = 848–56| year = 2002| last1 = Flier | first1 = W. G. | last2 = Grünwald | first2 = N. J. | last3 = Kroon | first3 = L. P. N. M. | last4 = Van Den Bosch | first4 = T. B. M. | last5 = Garay-Serrano | first5 = E. | last6 = Lozoya-Saldaña | first6 = H. | last7 = Bonants | first7 = P. J. M. | last8 = Turkensteen | first8 = L. J. | s2cid = 20294303}}

Others have proposed an Andean origin for Phytophthora infestans. In 2002, Ristaino assessed the evidence for both the Mexican and South American origin hypotheses [24]. She pointed to the absence of potato exports during the 1840s, which posed a challenge to the notion of a Mexican origin for the blight's migration to the US and Europe [24]. Furthermore, historical accounts of a similar disease in the Andean region and the presence of the cosmopolitan US-1 lineage in South America since at least the 1980s (yet absent in Mexico) were invoked by Ristaino, potentially supporting the idea of a South American origin [24]. In 2016, the Ristaino lab with collaborators Mike Martin and Tom Gilbert, at the University of Copenhagen, conducted the largest whole genome sequencing project to date with historic and modern day lineages of P infestans (25). Analysis of these more extensive genomic dataset that included both P. infestans and P. andina isolates documented an Andean origin of the species [25]. Lineages of Andean origin were found to be more closely related to historical P. infestans lineages from the famine era, implying an Andean origin with later subsequent migration and diversification occurring in Mexican lineages [25]. Significant admixture between the historic P infestans and P andina was also documented [25]. Several close relatives of P infestans have been found inthe Andes in South America, including P. andina,P urerae and P betacei.

Coomber et al., examined the evolutionary history of Phytophthora infestans and its close relatives in the 1c clade using whole genome sequence data from 69 isolates of Phytophthora species in the 1c clade and conducted a range of genomic analyses including nucleotide diversity evaluation, maximum likelihood trees, network assessment, time to most recent common ancestor and migration analysis [26}. They consistently identified distinct and later divergence of the two Mexican Phytophthora species, P. mirabilis and P. ipomoeae, from P. infestans and other 1c clade species. Phytophthora infestans exhibited more recent divergence from other 1c clade species of Phytophthora from South America, P. andina and P. betacei. Speciation in the 1c clade and evolution of P. infestans occurred in the Andes. P. andina – P. betacei – P. infestans formed a species complex with indistinct species boundaries, hybridizations between the species, and short times to common ancestry. Furthermore, the distinction between modern Mexican and South American P. infestans proved less discrete, suggesting gene flow between populations over time. Admixture analysis indicated a complex relationship among these populations, hinting at potential gene flow across these regions. Historic P. infestans, collected from 1845-1889 from herbarium collections, were the first to diverge from all other P. infestans populations. Modern South American populations diverged next followed by Mexican populations which showed later ancestry. Both populations were derived from historic P. infestans. Based on the time of divergence of P. infestans from its closest relatives, P. andina and P. betacei in the Andean region, the data support the Andes as the center of origin of P. infestans, with modern globalization contributing to admixture between P. infestans populations today from Mexico, the Andes and Europe [26].

Migrations from Mexico to North America or Europe have occurred several times throughout history, probably linked to the movement of tubers.{{Cite journal | doi = 10.1073/pnas.91.24.11591| pmid = 7972108| title = Panglobal distribution of a single clonal lineage of the Irish potato famine fungus| journal = Proceedings of the National Academy of Sciences| volume = 91| issue = 24| pages = 11591–95| year = 1994| last1 = Goodwin | first1 = S. B.| last2 = Cohen | first2 = B. A.| last3 = Fry | first3 = W. E.| pmc = 45277| bibcode = 1994PNAS...9111591G| doi-access = free}}{{Cite journal | doi = 10.7554/eLife.00731| pmid = 23741619| title = The rise and fall of the Phytophthora infestans lineage that triggered the Irish potato famine| journal = eLife| volume = 2| pages = e00731| year = 2013| last1 = Yoshida | first1 = K.| last2 = Schuenemann | first2 = V. J.| last3 = Cano | first3 = L. M.| last4 = Pais | first4 = M.| last5 = Mishra | first5 = B.| last6 = Sharma | first6 = R.| last7 = Lanz | first7 = C.| last8 = Martin | first8 = F. N.|last9=Kamoun|first9=Sophien|author9-link=Sophien Kamoun| last10 = Krause | first10 = J.| last11 = Thines | first11 = M.| last12 = Weigel | first12 = D.| last13 = Burbano | first13 = H. A.| pmc = 3667578| arxiv = 1305.4206| doi-access = free}} Until the 1970s, the A2 mating type was restricted to Mexico, but now in many regions of the world both A1 and A2 isolates can be found in the same region.{{Cite journal | doi = 10.1111/j.1364-3703.2007.00465.x| pmid = 18705878| title = Phytophthora infestans: The plant (and R gene) destroyer| journal = Molecular Plant Pathology| volume = 9| issue = 3| pages = 385–402| year = 2008| last1 = Fry | first1 = William E. | pmc = 6640234| bibcode = 2008MolPP...9..385F}} The co-occurrence of the two mating types is significant due to the possibility of sexual recombination and formation of oospores, which can survive the winter. Only in Mexico and Scandinavia, however, is oospore formation thought to play a role in overwintering.{{cite journal | doi=10.2137/1239099043633332 | title=Oospores of Phytphthora infestans in soil provide an important new source of primary inoculum in Finland | year=2008 | last1=Hannukkala | first1=A. | last2=Lehtinen | first2=A. | journal=Agricultural and Food Science | volume=13 | issue=4 | page=399 | doi-access=free }} In other parts of Europe, increasing genetic diversity has been observed as a consequence of sexual reproduction.{{Citation|title=Appraisal of artificial screening techniques of tomato to accurately reflect field performance of the late blight resistance|last=Nowakowska|first=Marzena|date=3 October 2014|doi=10.1371/journal.pone.0109328|display-authors=etal|volume=9|issue=10|journal=PLOS ONE|pages=e109328|pmid=25279467|pmc=4184844|bibcode=2014PLoSO...9j9328N|doi-access=free}} This is notable since different forms of P. infestans vary in their aggressiveness on potato or tomato, in sporulation rate, and sensitivity to fungicides.{{Cite news|url=http://phys.org/news/2016-12-evidence-movement-potato-famine-pathogen.html|title=Study provides evidence on movement of potato famine pathogen|access-date=29 December 2016}} Variation in such traits also occurs in North America, however importation of new genotypes from Mexico appears to be the predominant cause of genetic diversity, as opposed to sexual recombination within potato or tomato fields. In 1976 – due to a summer drought in Europe – there was a potato production shortfall and so eating potatoes were imported to fill the shortfall. It is thought that this was the vehicle for mating type A2 to reach the rest of the world. In any case, there had been little diversity, consisting of the US-1 strain, and of that only one type of: mating type, mtDNA, restriction fragment length polymorphism, and di-locus{{clarify|date=June 2021}} isozyme. Then in 1980 suddenly greater diversity and A2 appeared in Europe. In 1981 it was found in the Netherlands, United Kingdom, 1985 in Sweden, the early 1990s in Norway and Finland, 1996 in Denmark, and 1999 in Iceland. In the UK new A1 lineages only replaced the old lineage by end of the '80s, and A2 spread even more slowly, with Britain having low levels and Ireland (north and Republic) having none-to-trace detections through the '90s.{{cite journal | last1=Cooke | first1=L. R. | last2=Schepers | first2=H. T. A. M. | last3=Hermansen | first3=A. | last4=Bain | first4=R. A. | last5=Bradshaw | first5=N. J. | last6=Ritchie | first6=F. | last7=Shaw | first7=D. S. | last8=Evenhuis | first8=A. | last9=Kessel | first9=G. J. T. | last10=Wander | first10=J. G. N. | last11=Andersson | first11=B. | last12=Hansen | first12=J. G. | last13=Hannukkala | first13=A. | last14=Nærstad | first14=R. | last15=Nielsen | first15=B. J. | title=Epidemiology and Integrated Control of Potato Late Blight in Europe | journal=Potato Research | volume=54 | issue=2 | date=2011-05-24 | issn=0014-3065 | doi=10.1007/s11540-011-9187-0 | pages=183–222 | s2cid=21251642| doi-access=free }} Many of the strains that appeared outside of Mexico since the 1980s have been more aggressive, leading to increased crop losses. In Europe since 2013 the populations have been tracked by the EuroBlight network (see links below). Some of the differences between strains may be related to variation in the RXLR effectors that are present.

Disease management

P. infestans is still a difficult disease to control. There are many chemical options in agriculture for the control of damage to the foliage as well as the fruit (for tomatoes) and the tuber{{Cite web|url=https://www.plantvillage.org/en/topics/potato/infos/diseases_and_pests_description_uses_propagation|title=PlantVillage|access-date=2015-12-16|archive-date=2015-12-22|archive-url=https://web.archive.org/web/20151222152544/https://www.plantvillage.org/en/topics/potato/infos/diseases_and_pests_description_uses_propagation|url-status=dead}} (for potatoes). A few of the most common foliar-applied fungicides are Ridomil, a Gavel/SuperTin tank mix, and Previcur Flex. All of the aforementioned fungicides need to be tank mixed with a broad-spectrum fungicide, such as mancozeb or chlorothalonil, not just for resistance management but also because the potato plants will be attacked by other pathogens at the same time.

If adequate field scouting occurs and late blight is found soon after disease development, localized patches of potato plants can be killed with a desiccant (e.g. paraquat) through the use of a backpack sprayer. This management technique can be thought of as a field-scale hypersensitive response similar to what occurs in some plant-viral interactions whereby cells surrounding the initial point of infection are killed in order to prevent proliferation of the pathogen.

If infected tubers make it into a storage bin, there is a very high risk to the storage life of the entire bin. Once in storage, there is not much that can be done besides emptying the parts of the bin that contain tubers infected with Phytophthora infestans. To increase the probability of successfully storing potatoes from a field where late blight was known to occur during the growing season, some products can be applied just prior to entering storage (e.g., Phostrol).{{Cite news |last=Gevens |first=Amanda |date=March 23, 2019 |title=Expert advises on post-harvest treatment of common potato diseases |url=https://www.potatonewstoday.com/2019/03/23/expert-advises-on-post-harvest-treatment-of-common-potato-diseases/ |access-date=November 24, 2024 |work=Potato News Today}}

Around the world the disease causes around $6 billion of damage to crops each year.

=Resistant plants=

Image:Cisgenicpotatoes.JPG potatoes are healthy.]]

File:Älskade knöl – utflykt med SLU till deras potatisförsöksodlingar – 20190825 09 (cropped).jpg (right) next to King Edward which has not been genetically modified (left). Research field, Swedish University of Agricultural Sciences, 2019]]

Breeding for resistance, particularly in potato plants, has had limited success in part due to difficulties in crossing cultivated potato with its wild relatives, which are the source of potential resistance genes. In addition, most resistance genes work only against a subset of P. infestans isolates, since effective plant disease resistance results only when the pathogen expresses a RXLR effector gene that matches the corresponding plant resistance (R) gene; effector-R gene interactions trigger a range of plant defenses, such as the production of compounds toxic to the pathogen.

Potato and tomato 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 in the Northern Hemisphere). 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.{{Citation |last1=Novy |first1=R. G. |last2=Love |first2=S. L. |year=2006 |title=Defender: A high-yielding, processing potato cultivar with foliar and tuber resistance to late blight |journal=American Journal of Potato Research|volume=83 |issue=1 |pages=9–19 |doi=10.1007/BF02869605 |s2cid=41454585 |display-authors=etal}}

Genetic engineering may also provide options for generating resistance cultivars. A resistance gene effective against most known strains of blight has been identified from a wild relative of the potato, Solanum bulbocastanum, and introduced by genetic engineering into cultivated varieties of potato.{{Citation |last1=Song |first1=Junqi |last2=Bradeen |first2=James M. |last3=Naess |first3=S. Kristine |last4=Raasch |first4=John A. |last5=Wielgus |first5=Susan M. |last6=Haberlach |first6=Geraldine T. |last7=Liu |first7=Jia |last8=Kuang |first8=Hanhui |last9=Austin-Phillips |first9=Sandra |last10=Jiang |first10=Jiming |year=2003 |title=Gene RB cloned from Solanum bulbocastanum confers broad spectrum resistance to potato late blight |journal=Proceedings of the National Academy of Sciences |volume=100 |issue=16 |pages=9128–33 |doi=10.1073/pnas.1533501100 |pmid=12872003 |pmc=170883 |bibcode=2003PNAS..100.9128S |doi-access=free }} This is an example of cisgenic genetic engineering.{{Cite journal| last1 = Jacobsen | first1 = E.| last2 = Schouten | first2 = H. J.| title = Cisgenesis, a New Tool for Traditional Plant Breeding, Should be Exempted from the Regulation on Genetically Modified Organisms in a Step by Step Approach|journal=Potato Research| volume = 51| pages = 75–88| year = 2008| doi = 10.1007/s11540-008-9097-y| s2cid = 38742532}} [http://www.cisgenesis.com/images/pdfs/potato%20res.%202008%20jacobsen.pdf Free version] {{Webarchive|url=https://web.archive.org/web/20150923203713/http://www.cisgenesis.com/images/pdfs/potato%20res.%202008%20jacobsen.pdf |date=2015-09-23 }}

Melatonin in the plant/P. infestans co-environment reduces the stress tolerance of the parasite.{{cite journal

|last1=Socaciu

|first1=Andreea Iulia

|last2=Ionuţ

|first2=Răzvan

|last3=Socaciu

|first3=Mihai Adrian

|last4=Ungur

|first4=Andreea Petra

|last5=Bârsan

|first5=Maria

|last6=Chiorean

|first6=Angelica

|last7=Socaciu

|first7=Carmen

|last8=Râjnoveanu

|first8=Armand Gabriel

|title=Melatonin, an ubiquitous metabolic regulator: functions, mechanisms and effects on circadian disruption and degenerative diseases

|journal=Reviews in Endocrine and Metabolic Disorders

|volume=21

|issue=4

|date=2020-07-21

|issn=1389-9155

|doi=10.1007/s11154-020-09570-9

|pages=465–478

|pmid=32691289

|s2cid=220657247

}}

=Reducing inoculum=

Blight can be controlled by limiting the source of inoculum. Only good-quality seed potatoes and tomatoes obtained from certified suppliers should be planted. Often discarded potatoes from the previous season and self-sown tubers can act as sources of inoculum.{{Citation |last1=Zwankhuizen |first1=Maarten J. |last2=Govers |first2=Francine |last3=Zadoks |first3=Jan C. |author-link3=Jan Zadoks |year=1998 |title=Development of potato late blight epidemics: Disease foci, disease gradients, and infection sources |journal=Phytopathology |volume=88 |issue=8 |pages=754–63 |doi=10.1094/PHYTO.1998.88.8.754 |pmid=18944880 |doi-access= |bibcode=1998PhPat..88..754Z }}

Compost, soil or potting medium can be heat-treated to kill oomycetes such as Phytophthora infestans. The recommended sterilisation temperature for oomycetes is {{convert|120|F|C}} for 30 minutes.{{cite web|url=http://phytosphere.com/soilphytophthora/soilsterilization.htm|title=Phytophthora in nursery stock and restoration plantings|date=4 September 2017}}{{cite book|editor=Baker, K.|title=The U.C. System for Producing Healthy Container Grown Plants, Manual 23|date=1957|publisher=University of California, Division of Agricultural Sciences, Agricultural Experiment Station Extension Service}}

=Environmental conditions=

There are several environmental conditions that are conducive to P. infestans. An example of such took place in the United States during the 2009 growing season. As colder than average for the season and with greater than average rainfall, there was a major infestation of tomato plants, specifically in the eastern states.{{Citation |last=Moskin |first=Julia |date=17 July 2009 |title=Outbreak of Fungus Threatens Tomato Crop |newspaper=The New York Times |url=https://www.nytimes.com/2009/07/18/nyregion/18tomatoes.html }} 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.{{Citation |doi=10.1094/PD-65-394 |last=MacKenzie |first=D. R. |year=1981 |title=Scheduling fungicide applications for potato late blight with Blitecast |journal=Plant Disease |volume=65 |issue= 5|pages=394–99 }}

A {{ Visible anchor |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 {{convert|10|°C|°F}} and 75%, respectively.{{cite web|url=http://botanydictionary.org/beaumont-period.html|website=botanydictionary.org|title=Beaumont period|access-date=3 March 2013}}{{cite web|url=http://archive.bio.ed.ac.uk/jdeacon/microbes/blight.htm|title=The Microbial World: Potato blight – Phytophthora infestans|access-date=3 March 2013}}
A {{ Visible anchor |Smith Period}} is at least two consecutive days where min temperature is {{convert|10|°C|°F}} or above and on each day at least 11 hours when the relative humidity is greater than 90%.

The Beaumont and Smith periods have traditionally been used by growers in the United Kingdom, with different criteria developed by growers in other regions. The Smith period has been the preferred system used in the UK since its introduction in the 1970s.{{cite web|url=http://www.bspp.org.uk/publications/bsppnews/bsppnews42/bsppnews42f.htm|publisher=The British Society for Plant Pathology|title=Obituary: L. Smith|access-date=3 March 2013}}

Based on these conditions and other factors, several tools have been developed to help growers manage the disease and plan fungicide applications. Often these are deployed as part of decision support systems accessible through web sites or smart phones.

Several studies have attempted to develop systems for real-time detection via flow cytometry or microscopy of airborne sporangia collected in air samplers.{{Cite journal|author1=Day, J.P. |author2=D.B. Kell |author3=G.W. Griffith |date=2001|title=Differentiation of Phytophthora infestans sporangia from other airborne biological particles by flow cytometry|journal=Applied and Environmental Microbiology|volume=68 |issue=1|pages=37–45|doi=10.1128/AEM.68.1.37-45.2002|pmid=11772606 |pmc=126536}}{{Cite conference |author=Griffith, G.W. |author2=J.P. Day |author3=D.B. Kell|date=2002|title=Use of flow cytometry in the detection of plant pathogenic spores|book-title=British Crop Protection Conference, Brighton, Nov 2002|volume=1|pages=417–24|url=https://users.aber.ac.uk/gwg/pdf/Griffith-BCPCflowcyt.pdf}}{{Cite journal|last1=Fall|first1=M. L.|last2=Van der Heyden|first2=H.|last3=Brodeur|first3=L.|last4=Leclerc|first4=Y.|last5=Moreau|first5=G.|last6=Carisse|first6=O.|date=6 June 2014 |title=Spatiotemporal variation in airborne sporangia of Phytophthora infestans: characterization and initiatives towards improving potato late blight risk estimation|journal=Plant Pathology|volume=64|issue=1|pages=178–90|doi=10.1111/ppa.12235|issn=0032-0862|doi-access=free}} Whilst these methods show potential to allow detection of sporangia in advance of occurrence of detectable disease symptoms on plants, and would thus be useful in enhancing existing decision support systems, none have been commercially deployed to date.

=Use of fungicides=

File:Potato blight spraying system.jpg potato, Nottinghamshire]]

Fungicides for the control of potato blight are normally used only in a preventative manner, optionally in conjunction with disease forecasting. In susceptible varieties, sometimes fungicide applications may be needed weekly. An early spray is most effective. The choice of fungicide can depend on the nature of local strains of P. infestans. Metalaxyl is a fungicide that was marketed for use against P. infestans, but suffered serious resistance issues when used on its own. In some regions of the world during the 1980s and 1990s, most strains of P. infestans became resistant to metalaxyl, but in subsequent years many populations shifted back to sensitivity. To reduce the occurrence of resistance, it is strongly advised to use single-target fungicides such as metalaxyl along with carbamate compounds. A combination of other compounds are recommended for managing metalaxyl-resistant strains. These include mandipropamid, chlorothalonil, fluazinam, triphenyltin, mancozeb, and others. In the United States, the Environmental Protection Agency has approved oxathiapiprolin for use against late blight.{{cite web | url = http://www.mda.state.mn.us/chemicals/pesticides/regs/~/media/Files/chemicals/reviews/nair-oxathiapiprolin.pdf | title = Oxathiapiprolin |website= New Active Ingredient Review | date = October 2015 | publisher = Minnesota Department of Agriculture | access-date = 2017-11-09 | archive-url = https://web.archive.org/web/20171107025015/http://www.mda.state.mn.us/chemicals/pesticides/regs/~/media/Files/chemicals/reviews/nair-oxathiapiprolin.pdf | archive-date = 2017-11-07 }} In African smallholder production fungicide application can be necessary up to once every three days.{{cite web | last=Daba | first=Tadessa | title=Why a new potato variety could be a game-changed for farmers in East Africa |website=Alliance for Science | date=2020-12-11 | url=http://allianceforscience.cornell.edu/blog/2020/12/why-a-new-potato-variety-could-be-a-game-changed-for-farmers-in-east-africa/ | access-date=2021-09-01}}

==In organic production==

In the past, copper(II) sulfate solution (called 'bluestone') was used to combat potato blight. Copper pesticides remain in use on organic crops, both in the form of copper hydroxide and copper sulfate. Given the dangers of copper toxicity, other organic control options that have been shown to be effective include horticultural oils, phosphorous acids, and rhamnolipid biosurfactants, while sprays containing "beneficial" microbes such as Bacillus subtilis or compounds that encourage the plant to produce defensive chemicals (such as knotweed extract) have not performed as well.Gevens, Amanda, University of Wisconsin Madison Extension. [http://www.plantpath.wisc.edu/wivegdis/pdf/2013/Organic%20late%20blight%20control%202013.pdf Managing Late Blight in Organic Tomato & Potato Crops] {{Webarchive|url=https://web.archive.org/web/20140618023311/http://www.plantpath.wisc.edu/wivegdis/pdf/2013/Organic%20late%20blight%20control%202013.pdf |date=2014-06-18 }}.

During the crop year 2008, many of the certified organic potatoes produced in the United Kingdom and certified by the Soil Association as organic were sprayed with a copper pesticide{{cite web | url=http://organicstandard.ua/files/standards/en/soil/Soil%20Association%20Organic%20Standards%20for%20Producers%202009.pdf | archive-url=https://web.archive.org/web/20210901204043/http://organicstandard.ua/files/standards/en/soil/Soil%20Association%20Organic%20Standards%20for%20Producers%202009.pdf | archive-date=2021-09-01 | title=Soil Association organic standards for producers | date=January 2009 | version=16; section 4.11.11|page=103| publisher=Soil Association}} to control potato blight. According to the Soil Association, the total copper that can be applied to organic land is {{convert|6|kg/ha|lb/acre}}/year.{{cite web|url=http://www.soilassociation.org/Certification/Servicesforlicensees/Forms/Horticultureandarable/tabid/406/Default.aspx|title=Links to forms permitting application of copper fungicide on the website of the Soil Association|publisher=Soilassociation.org|archive-url=https://web.archive.org/web/20091015055455/http://www.soilassociation.org/Certification/Servicesforlicensees/Forms/Horticultureandarable/tabid/406/Default.aspx|archive-date=15 October 2009|access-date=16 July 2010}}

=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.{{Citation |last1=Glass |first1=J. R. |last2=Johnson |first2=K. B. |last3=Powelson |first3=M. L. |year=2001 |title=Assessment of Barriers to Prevent the Development of Potato Tuber Blight |journal=Plant Disease|volume=85 |issue=5 |pages=521–28 |doi=10.1094/PDIS.2001.85.5.521 |pmid=30823129 |doi-access= }} Another approach is to destroy the canopy around five weeks before harvest, using a contact herbicide or sulfuric acid to burn off the foliage. Eliminating infected foliage reduces the likelihood of tuber infection.

Historical impact

File:19th century late blight in US.webp

The first recorded instances of the disease were in the United States, in Philadelphia and New York City in early 1843.{{Cite journal |last1=Saeffer |first1=A |last2=Tateosian |first2=L. A. |last3=Yang |first3=Y. P. |last4=Saville |first4=A |last5=Ristaino |first5=J. B. |date=2024 |title=Reconstructing 19th century and modern potato late blight outbreaks using text analytics. |journal=Scientific Reports |url=https://doi.org/10.1038/s41598-024-52870-2 |access-date= |volume=14 |issue=1 |page=14:2523|doi=10.1038/s41598-024-52870-2 |pmid=38360880 |pmc=10869797 }} 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.{{Citation |first=John |last=Reader |title=The Fungus That Conquered Europe |url=https://www.nytimes.com/2008/03/17/opinion/17reader.html |work=New York Times |date=17 March 2008 |access-date=18 March 2008}}{{cite web | url=https://www.rte.ie/history/the-great-irish-famine/2022/0127/1276178-the-hungry-forties-in-europe | title=Between two worlds: The Hungry Forties in Europe | website=RTÉ.ie | date=27 January 2022 }} The disease being first identified in Europe around Kortrijk, Belgium, in June 1845, and resulted in the Flemish potato harvest failing that summer, yields declining 75–80%, leading to an estimated forty thousand deaths in the locale.{{Cite web |last=Vlaanderen |first=Canon van |title=The Potato Crisis |url=https://www.canonvanvlaanderen.be/en/events/the-potato-crisis/ |access-date=2024-06-08 |website=Canon van Vlaanderen }} All of the potato-growing countries in Europe would be affected within a year.

The effect of Phytophthora infestans in Ireland in 1845–52 was one of the factors which caused more than one million to starve to death{{cite journal |last=Bourouiba |first=Lydia |date=2021-01-05 |title=The Fluid Dynamics of Disease Transmission |journal=Annual Review of Fluid Mechanics |volume=53 |issue=1 |pages=473–508 |bibcode=2021AnRFM..53..473B |doi=10.1146/annurev-fluid-060220-113712 |issn=0066-4189 |s2cid=225114407 |doi-access=free}} and forced another two million to emigrate. Most commonly referenced is the Great Irish Famine, during the late 1840s. Implicated in Ireland's fate was the island's disproportionate dependency on a single variety of potato, the Irish Lumper. The lack of genetic variability created a susceptible host population for the organism{{cite web

| title = Great Famine potato makes a comeback after 170 years

| publisher = IrishCentral

| url = http://www.irishcentral.com/news/Great-Famine-potato-makes-a-comeback-after-170-years-194635321.html

| access-date = 2013-03-05 | date = 2013-03-03

}} after the blight strains originating in Chiloé Archipelago replaced earlier potatoes of Peruvian origin in Europe.{{Cite news|title=Mash hits: the land that spawned the supermarket spud|url=https://www.economist.com/1843/2020/08/28/mash-hits-the-land-that-spawned-the-supermarket-spud|last=Johanson|first=Mark|date=August 28, 2020|access-date=September 1, 2020|newspaper=The Economist}}

During the First World War, all of the copper in Germany was used for shell casings and electric wire and therefore none was available for making copper sulfate to spray potatoes. A major late blight outbreak on potato in Germany therefore went untreated, and the resulting scarcity of potatoes contributed to the deaths from the blockade.{{Cite web |url=http://www.botany.hawaii.edu/faculty/wong/BOT135/LECT06.HTM |title=The Origin of Plant Pathology and The Potato Famine, and Other Stories of Plant Diseases. |access-date=2018-09-01 |archive-url=https://web.archive.org/web/20160304001917/http://www.botany.hawaii.edu/faculty/wong/BOT135/LECT06.HTM |archive-date=2016-03-04 }}{{cite book|page=88|last1=Carefoot|first1= G.L. |last2=Sprott |first2= E.R. |year= 1967| title= Famine on the Wind: Man's Battle Against Plant Disease| publisher= Rand McNally}}

Since 1941, Eastern Africa has been suffering potato production losses because of strains of P. infestans from Europe.{{cite journal |title= Genotyping of Phytophthora infestans in Eastern Africa Reveals a Dominating Invasive European Lineage|journal=Phytopathology|volume=109|issue=4|pages=670–680|doi=10.1094/PHYTO-07-18-0234-R|year=2019|last1=Njoroge|first1=Anne W.|last2=Andersson|first2=Björn|last3=Lees|first3=Alison K.|last4=Mutai|first4=Collins|last5=Forbes|first5=Gregory A.|last6=Yuen|first6=Jonathan E.|last7=Pelle|first7=Roger|pmid=30253119 |doi-access=free|bibcode=2019PhPat.109..670N }}

France, Canada, the United States, and the Soviet Union researched P. infestans as a biological weapon in the 1940s and 1950s.{{Citation |last1=Suffert |first1=Frédéric |last2=Latxague |first2=Émilie |last3=Sache |first3=Ivan |year=2009 |title=Plant pathogens as agroterrorist weapons: assessment of the threat for European agriculture and forestry |journal=Food Security|volume=1 |issue=2 |pages=221–232 |doi=10.1007/s12571-009-0014-2 |s2cid=23830595 }} 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."[http://cns.miis.edu/cbw/possess.htm 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. Dr. Mannon Gallegley, deceased faculty from WVA worked in the late blight bioweapons program in the 1940s. It is unclear whether the pathogen was ever deployed. Whether a weapon based on the pathogen would be effective is questionable, due to the difficulties in delivering viable pathogen to an enemy's fields, and the role of uncontrollable environmental factors in spreading the disease.{{Cite journal |last1=Casadevall |first1=Arturo |last2=Pirofski |first2=Liise-anne |date=June 2004 |title=The weapon potential of a microbe |journal=Trends in Microbiology |volume=12 |issue=6 |pages=259–263 |doi=10.1016/j.tim.2004.04.007 |issn=0966-842X |pmc=7133335 |pmid=15165603}}

Late blight (A2 type) has not yet been detected in Australia and strict biosecurity measures are in place. The disease has been seen in China, India and south-east Asian countries.

A large outbreak of P. infestans occurred on tomato plants in the Northeast United States in 2009.{{Cite web |title=The 2009 Late Blight Pandemic in Eastern USA |url=https://www.apsnet.org/edcenter/apsnetfeatures/Pages/2009LateBlight.aspx |access-date=2023-11-24 |website=The 2009 Late Blight Pandemic in Eastern USA }}

In light of the periodic epidemics of P. infestans ever since its first emergence, it may be regarded as a periodically emerging pathogen – or a periodically "re-emerging pathogen".{{cite journal |last1=Fones |first1=Helen N. |last2=Bebber |first2=Daniel P. |last3=Chaloner |first3=Thomas M. |last4=Kay |first4=William T. |last5=Steinberg |first5=Gero |last6=Gurr |first6=Sarah J. |title=Threats to global food security from emerging fungal and oomycete crop pathogens |journal=Nature Food |volume=1 |issue=6 |date=2020-06-02 |issn=2662-1355 |doi=10.1038/s43016-020-0075-0 |pages=332–342 |pmid=37128085 |s2cid=219924805}}{{snd}}({{cite journal |last1=Fones |first1=Helen N. |last2=Bebber |first2=Daniel P. |last3=Chaloner |first3=Thomas M. |last4=Kay |first4=William T. |last5=Steinberg |first5=Gero |last6=Gurr |first6=Sarah J. |display-authors=0 |title=Author Correction: Threats to global food security from emerging fungal and oomycete crop pathogens |journal=Nature Food |volume=1 |issue=7 |year=2020 |issn=2662-1355 |doi=10.1038/s43016-020-0111-0 |pages=455–456 |doi-access=free}}){{cite journal | last1=Fry | first1=W. E. | last2=Birch | first2=P. R. J. | last3=Judelson | first3=H. S. | last4=Grünwald | first4=N. J. | last5=Danies | first5=G. | last6=Everts | first6=K. L. | last7=Gevens | first7=A. J. | last8=Gugino | first8=B. K. | last9=Johnson | first9=D. A. | last10=Johnson | first10=S. B. | last11=McGrath | first11=M. T. | last12=Myers | first12=K. L. | last13=Ristaino | first13=J. B. | last14=Roberts | first14=P. D. | last15=Secor | first15=G. | last16=Smart | first16=C. D. | title=Five Reasons to Consider Phytophthora infestans a Reemerging Pathogen | journal=Phytopathology | volume=105 | issue=7 | year=2015 | issn=0031-949X | doi=10.1094/phyto-01-15-0005-fi | pages=966–981 | pmid=25760519 | s2cid=27658217| doi-access=free | bibcode=2015PhPat.105..966F }}

References

{{Reflist|refs=

{{cite web | title=Biotech Potato Keeps Late Blight Disease in Check, New Study Finds |website=International Potato Center | date=2019-02-21 | url=http://cipotato.org/blog/biotech-potato/ | access-date=2020-12-21}}

{{cite journal | last1=Ghislain | first1=Marc | last2=Byarugaba | first2=Arinaitwe Abel | last3=Magembe | first3=Eric | last4=Njoroge | first4=Anne | last5=Rivera | first5=Cristina | last6=Román | first6=María Lupe | last7=Tovar | first7=José Carlos | last8=Gamboa | first8=Soledad | last9=Forbes | first9=Gregory A. | last10=Kreuze | first10=Jan F. | last11=Barekye | first11=Alex | last12=Kiggundu | first12=Andrew | title=Stacking three late blight resistance genes from wild species directly into African highland potato varieties confers complete field resistance to local blight races | journal=Plant Biotechnology Journal | volume=17 | issue=6 | date=2018-12-21 | issn=1467-7644 | doi=10.1111/pbi.13042 | pages=1119–1129| pmid=30467980 | pmc=6523587 }}

{{cite web|url=http://modernfarmer.com/2020/12/why-a-new-potato-variety-could-be-a-game-changer-for-farmers-in-east-africa/|title=Why a New Potato Variety Could Be a Game-Changer for Farmers in East Africa|first=Tadessa|last=Daba|date=2020-12-16|website=Modern Farmer}}

}}

External links

[http://www.USAblight.org USAblight A National Web Portal on Late Blight]
[http://www.cipotato.org International Potato Center]
[https://web.archive.org/web/20061014125542/http://www.btny.purdue.edu/USDA-ARS/Goodwin_lab/results/Phytoph_biblio.html Online Phytophtora bibliography]
[http://www.euroblight.net EuroBlight a potato blight network in Europe]
[https://web.archive.org/web/20050519074314/http://www.barc.usda.gov/psi/vl/lateblight.htm USDA-BARC Phytophthora infestans page]
[https://attra.ncat.org/attra-pub-summaries/?pub=123 Organic Alternatives for Late Blight Control in Potatoes, from ATTRA] {{Webarchive|url=https://web.archive.org/web/20200925005014/https://attra.ncat.org/attra-pub-summaries/?pub=123 |date=2020-09-25 }}
[http://uspest.org/risk/tom_pot_map Google Map of Tomato Potato Blight Daily Risk across NE USA]
[https://www.invasivespeciesinfo.gov/profile/late-blight Species Profile – Late Blight (Phytophthora infestans)], National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Late Blight.
[http://www.apsnet.org/edcenter/intropp/lessons/fungi/oomycetes/pages/lateblight.aspx Continuing education lesson] created by The American Phytopathological Society
[https://plantvillage.org/topics/potato/infos entry on Late Blight] by PlantVillage

infestans

Category:Water mould plant pathogens and diseases

Category:Potato diseases

Category:Biological agents