Phytophthora Infestans
   HOME

TheInfoList



OR:

''Phytophthora infestans'' is an
oomycete The Oomycetes (), or Oomycota, form a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms within the Stramenopiles. They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction o ...
or water mold, a fungus-like
microorganism A microorganism, or microbe, is an organism of microscopic scale, microscopic size, which may exist in its unicellular organism, single-celled form or as a Colony (biology)#Microbial colonies, colony of cells. The possible existence of unseen ...
that causes the serious
potato The potato () is a starchy tuberous vegetable native to the Americas that is consumed as a staple food in many parts of the world. Potatoes are underground stem tubers of the plant ''Solanum tuberosum'', a perennial in the nightshade famil ...
and
tomato The tomato (, ), ''Solanum lycopersicum'', is a plant whose fruit is an edible Berry (botany), berry that is eaten as a vegetable. The tomato is a member of the nightshade family that includes tobacco, potato, and chili peppers. It originate ...
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
famine A famine is a widespread scarcity of food caused by several possible factors, including, but not limited to war, natural disasters, crop failure, widespread poverty, an Financial crisis, economic catastrophe or government policies. This phenom ...
s. The organism can also infect some other members of the
Solanaceae Solanaceae (), commonly known as the nightshades, is a family of flowering plants in the order Solanales. It contains approximately 2,700 species, several of which are used as agricultural crops, medicinal plants, and ornamental plants. Many me ...
. The pathogen is favored by moist, cool environments: sporulation is optimal at in water-saturated or nearly saturated environments, and
zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion in aqueous or moist environments. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Certain zoospores are ...
production is favored at temperatures below . Lesion growth rates are typically optimal at a slightly warmer temperature range of .


Etymology

The genus name ''Phytophthora'' comes from the Greek (), meaning 'plant' – plus the Greek (), meaning 'decay, ruin, perish'. The species name ''infestans'' is the present participle of the Latin verb , 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 Heinrich Anton de Bary (26 January 183119 January 1888) was a German surgeon, botanist, microbiologist, and mycologist (fungal systematics and physiology). He is considered a founding father of plant pathology (phytopathology) as well as the fou ...
(1831–1888).


Life cycle, signs and symptoms

The asexual life cycle of ''Phytophthora infestans'' is characterized by alternating phases of
hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one o ...
l growth, sporulation,
sporangia A sporangium (from Late Latin, ; : sporangia) is an enclosure in which spores are formed. It can be composed of a unicellular organism, single cell or can be multicellular organism, multicellular. Virtually all plants, fungus, fungi, and many ot ...
germination (either through
zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion in aqueous or moist environments. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Certain zoospores are ...
release or direct germination, i.e. germ tube emergence from the
sporangium A sporangium (from Late Latin, ; : sporangia) is an enclosure in which spores are formed. It can be composed of a unicellular organism, single cell or can be multicellular organism, multicellular. Virtually all plants, fungus, fungi, and many ot ...
), and the re-establishment of hyphal growth. There is also a sexual cycle, which occurs when isolates of opposite mating type (A1 and A2, see below) meet. Hormonal communication triggers the formation of the sexual
spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
s, called oospores. 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 A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...
plants. The zoospores released from sporangia are biflagellated and
chemotactic Chemotaxis (from '' chemo-'' + ''taxis'') is the movement of an organism or entity in response to a chemical stimulus. Somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemica ...
, 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. The sporangia and sporangiophores appear white on the lower surface of the foliage. As for tuber blight, the white
mycelium Mycelium (: mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Its normal form is that of branched, slender, entangled, anastomosing, hyaline threads. Fungal colonies composed of mycelium are fo ...
often shows on the tubers' surface. 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 and humidity is over 75–80% for 2 days or more.
Rain Rain is a form of precipitation where water drop (liquid), droplets that have condensation, condensed from Water vapor#In Earth's atmosphere, atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is res ...
can wash spores into the
soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...
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
propagule In biology, a propagule is any material that functions in propagating an organism to the next stage in its life cycle, such as by dispersal. The propagule is usually distinct in form from the parent organism. Propagules are produced by organisms ...
s) at the start of a growing season. This can have devastating effects by destroying entire crops.


Mating types

The mating types are broadly divided into A1 and A2. 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 The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
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 Diterpenes are a class of terpenes composed of four isoprene units, often with the molecular formula C20H32. They are biosynthesized by plants, animals and fungi via the HMG-CoA reductase pathway, with geranylgeranyl pyrophosphate being a primary ...
α1. Clonal lineages of A1 include: * CN-1, -2, -4, -5, -6, -7, -8 – mtDNA haplotype Ia, China in 1996–97 * – Ia, China, 1996–97 * – Ia, China, 2004 * – IIb, China, 2000 & 2002 * – IIa, China, 2004–09 * – Ia/IIb, China, 2004–09 * – (only presumed to be A1), mtDNA haplo Ia subtype , Japan, Philippines, India, China, Malaysia, Nepal, present some time before 1950 * – Ia, India, Nepal, 1993 * – Ia, India, 1993 * JP-2/SIB-1/RF006 – mtDNA haplo IIa, distinguishable by RG57, intermediate level of metalaxyl resistance, Japan, China, Korea, Thailand, 1996–present * – IIa, distinguishable by RG57, intermediate level of metalaxyl resistance, Japan, 1996–present * – IIa, distinguishable by RG57, intermediate level of metalaxyl resistance, Japan, 1996–present * ''sensu'' Zhang (not to be confused with #KR-1 ''sensu'' Gotoh below) – IIa, Korea, 2002–04 * KR_1_A1 – mtDNA haplo unknown, Korea, 2009–16 * – Ia, China, 2004 * – Ia, India, Nepal, 1993, 1996–97 * – Ia, Nepal, 1997 * – Ia, Nepal, 1999–2000 * – (Also A2, see #the A2 type of NP2 below) Ia, Nepal, 1999–2000 * (not to be confused with #US-1 below) – Ib, Nepal, 1999–2000 * (not to be confused with #NP3/US-1 above) – Ib, China, India, Nepal, Japan, Taiwan, Thailand, Vietnam, 1940–2000 * – Ia, Nepal, 1999–2000 * – mtDNA haplo unknown, Nepal, 1999–2000 * – IIb, Taiwan, Korea, Vietnam, 1998–2016 * – IIb, China, 2002 & 2004 * – IIa, Korea, 2003–04 * * * – Ia, Indonesia, 2016–19 *


A2

Discovered by John Niederhauser in the 1950s, in the
Toluca Valley The Toluca Valley is a valley in central Mexico, just west of the Valley of Mexico (Mexico City), the old name was Matlatzinco. The valley runs north–south for about , surrounded by mountains, the most imposing of which is the Nevado de Toluca V ...
in Central Mexico, while working for the
Rockefeller Foundation The Rockefeller Foundation is an American private foundation and philanthropic medical research and arts funding organization based at 420 Fifth Avenue, New York City. The foundation was created by Standard Oil magnate John D. Rockefeller (" ...
'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 * – with
mtDNA Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the DNA contained in ...
haplotype A haplotype (haploid genotype) is a group of alleles in an organism that are inherited together from a single parent. Many organisms contain genetic material (DNA) which is inherited from two parents. Normally these organisms have their DNA orga ...
H-20 * – IIa, Japan, Korea, Indonesia, late 1980s–present * ''sensu'' Gotoh (not to be confused with #KR-1 ''sensu'' Zhang above) – IIa, differs from JP-1 by one RG57 band, Korea, 1992 * – mtDNA haplo unknown, Korea, 2009–16 * – Ia, China, 2001 * – (Also A1, see #the A1 type of NP2 above) Ia, Nepal, 1999–2000 * – Ib, Nepal, 1999–2000 * – Ia, Nepal, 1999–2000 * – Ia, Thailand, China, Nepal, 1994 & 1997 * Unknown – Ib, India, 1996–2003 * – Brazil * * * – IIa, Korea, 2002–03 * /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

is the in ''P. infestans''. Hosts respond with
autophagy Autophagy (or autophagocytosis; from the Greek language, Greek , , meaning "self-devouring" and , , meaning "hollow") is the natural, conserved degradation of the cell that removes unnecessary or dysfunctional components through a lysosome-depe ...
upon detection of this elicitor, Liu et al. 2005 finding this to be the only alternative to mass
hypersensitivity Hypersensitivity (also called hypersensitivity reaction or intolerance) is an abnormal physiological condition in which there is an undesirable and adverse immune response to an antigen. It is an abnormality in the immune system that causes Imm ...
leading to mass
programmed cell death Programmed cell death (PCD) sometimes referred to as cell, or cellular suicide is the death of a cell (biology), cell as a result of events inside of a cell, such as apoptosis or autophagy. PCD is carried out in a biological process, which usual ...
.


Genetics

''P. infestans'' is
diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...
, with about 8–10
chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...
s, and in 2009 scientists completed the sequencing of its
genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...
. 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
gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
s were detected within the ''P. infestans'' genome. It also contained a diverse variety of
transposon A transposable element (TE), also transposon, or jumping gene, is a type of mobile genetic element, a nucleic acid sequence in DNA that can change its position within a genome. The discovery of mobile genetic elements earned Barbara McClinto ...
s and many
gene families A gene family is a set of several similar genes, formed by duplication of a single original gene, and generally with similar biochemical functions. One such family are the genes for human hemoglobin subunits; the ten genes are in two clusters on ...
encoding for effector proteins that are involved in causing
pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...
icity. 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 The ''apoplast '' is the extracellular space outside of plant cell membranes, especially the fluid-filled cell walls of adjacent cells where water and dissolved material can flow and diffuse freely. Fluid and material flows occurring in any extr ...
(between plant cells). Proteins produced in the symplast included RXLR proteins, which contain an
arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidinium, guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) a ...
-X-
leucine Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins. Leucine is an α-amino acid, meaning it contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α-Car ...
-arginine (where X can be any
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...
) sequence at the
amino terminus The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the amin ...
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
protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalysis, catalyzes proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the formation of new protein products ...
s,
lipase In biochemistry, lipase ( ) refers to a class of enzymes that catalyzes the hydrolysis of fats. Some lipases display broad substrate scope including esters of cholesterol, phospholipids, and of lipid-soluble vitamins and sphingomyelinases; howe ...
s and glycosylases that act to degrade plant tissue,
enzyme inhibitor An enzyme inhibitor is a molecule that binds to an enzyme and blocks its Enzyme activity, activity. Enzymes are proteins that speed up chemical reactions necessary for life, in which Substrate (biochemistry), substrate molecules are converted ...
s to protect against host defence enzymes and
necrotizing Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. The term "necrosis" came about in the mid-19th century and is commonly attributed to German pathologist Rudolf Virchow, who is ...
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. The pathogen shows high allelic diversity in many isolates collected in
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
. This may be due to widespread
trisomy A trisomy is a type of polysomy in which there are three instances of a particular chromosome, instead of the normal two. A trisomy is a type of aneuploidy (an abnormal number of chromosomes). Description and causes Most organisms that reprod ...
or
polyploidy Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...
in those populations.


Research

Study Study or studies may refer to: General * Education **Higher education * Clinical trial * Experiment * Field of study * Observational study * Scientific study * Research * Study skills, abilities and approaches applied to learning Other * Study ...
of ''P. infestans'' presents sampling difficulties in the United States. It occurs only sporadically and usually has significant
founder effect In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. It was first fully outlined by Ernst Mayr in 1942, us ...
s due to each epidemic starting from introduction of a single
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
.


Origin and diversity

The highlands of central
Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
were considered to be the center of origin of ''P. infestans'', although others have proposed its origin to be in the
Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...
, which is also the origin of potatoes. A study published in 2014 evaluated these two alternate hypotheses and found conclusive support for central Mexico being the center of origin. However, their study did not include either an extensive global sampling of ''P. infestans'' or historic genomes. Support for a Mexican origin specifically the
Toluca Valley The Toluca Valley is a valley in central Mexico, just west of the Valley of Mexico (Mexico City), the old name was Matlatzinco. The valley runs north–south for about , surrounded by mountains, the most imposing of which is the Nevado de Toluca V ...
came from multiple observations including the fact that populations are genetically most diverse in Mexico, late blight is observed in native tuber-bearing ''
Solanum ''Solanum'' is a large and diverse genus of flowering plants, which include three food crops of high economic importance: the potato, the tomato and the eggplant (aubergine, brinjal). It is the largest genus in the nightshade family Solana ...
'' 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. 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. Others have proposed an Andean origin for ''Phytophthora infestans.'' In 2002, Ristaino assessed the evidence for both the Mexican and South American origin hypotheses 4 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 4 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 4 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 5 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 5 Significant admixture between the historic ''P infestans'' and ''P andina'' was also documented 5 Several close relatives of P infestans have been found inthe Andes in
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
, 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 Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
have occurred several times throughout history, probably linked to the movement of tubers. 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. 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 Scandinavia is a subregion#Europe, subregion of northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. ''Scandinavia'' most commonly refers to Denmark, Norway, and Sweden. It can sometimes also ...
, however, is oospore formation thought to play a role in overwintering. In other parts of Europe, increasing genetic diversity has been observed as a consequence of sexual reproduction. This is notable since different forms of ''P. infestans'' vary in their aggressiveness on potato or tomato, in sporulation rate, and sensitivity to
fungicide Fungicides are pesticides used to kill parasitic fungi or their spores. Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals, ...
s. Variation in such traits also occurs in North America, however importation of new
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
s 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 In molecular biology, restriction fragment length polymorphism (RFLP) is a technique that exploits variations in homologous DNA sequences, known as polymorphisms, populations, or species or to pinpoint the locations of genes within a sequence. T ...
, and di-locus
isozyme In biochemistry, isozymes (also known as isoenzymes or more generally as multiple forms of enzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. Isozymes usually have different kinetic parameters (e.g. di ...
. 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. 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 Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...
for the control of damage to the
foliage A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, f ...
as well as the fruit (for tomatoes) and the
tuber Tubers are a type of enlarged structure that plants use as storage organs for nutrients, derived from stems or roots. Tubers help plants perennate (survive winter or dry months), provide energy and nutrients, and are a means of asexual reproduc ...
(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 Mancozeb is a dithiocarbamate non-systemic agricultural fungicide with multi-site, protective action on contact. It is a combination of two other dithiocarbamates: maneb and zineb. The mixture controls many fungal diseases in a wide range of fi ...
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 A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccant ...
(e.g.
paraquat Paraquat ( trivial name; ), or ''N'',''N''′-dimethyl-4,4′-bipyridinium dichloride (systematic name), also known as methyl viologen, is a toxic organic compound with the chemical formula C6H7N)2l2. It is classified as a viologen, a family o ...
) 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). Around the world the disease causes around $6 billion of damage to crops each year.


Resistant plants

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 The Ranger Russet is a late-maturing potato that is used for baking and processing into fries. It was originally bred by Joseph J. Pavek of the USDA in Aberdeen, Idaho,Paul R. Wonning and released jointly by the USDA and the agricultural statio ...
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. 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. This is an example of cisgenic genetic engineering.
Melatonin Melatonin, an indoleamine, is a natural compound produced by various organisms, including bacteria and eukaryotes. Its discovery in 1958 by Aaron B. Lerner and colleagues stemmed from the isolation of a substance from the pineal gland of cow ...
in the plant/''P. infestans'' co-environment reduces the stress tolerance of the parasite.


Reducing inoculum

Blight can be controlled by limiting the source of inoculum. Only good-quality seed potatoes and tomatoes obtained from
certified Certification is part of testing, inspection and certification and the provision by an independent body of written assurance (a certificate) that the product, service or system in question meets specific requirements. It is the formal attestatio ...
suppliers should be planted. Often discarded potatoes from the previous
season A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's axial tilt, tilted orbit around the Sun. In temperat ...
and self-sown
tuber Tubers are a type of enlarged structure that plants use as storage organs for nutrients, derived from stems or roots. Tubers help plants perennate (survive winter or dry months), provide energy and nutrients, and are a means of asexual reproduc ...
s can act as sources of inoculum.
Compost Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical, and biological properties. It is commonly prepared by Decomposition, decomposing plant and food waste, recycling organic materials, and man ...
, soil or potting medium can be heat-treated to kill oomycetes such as ''Phytophthora infestans''. The recommended sterilisation temperature for oomycetes is for 30 minutes.


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. By using
weather forecasting Weather forecasting or weather prediction is the application of science and technology forecasting, to predict the conditions of the Earth's atmosphere, atmosphere for a given location and time. People have attempted to predict the weather info ...
systems, such as BLITECAST, if the following conditions occur as the
canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an a ...
of the crop closes, then the use of
fungicide Fungicides are pesticides used to kill parasitic fungi or their spores. Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals, ...
s is recommended to prevent an
epidemic An epidemic (from Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of hosts in a given population within a short period of time. For example, in meningococcal infection ...
. * A is a period of 48 consecutive hours, in at least 46 of which the hourly readings of
temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
and
relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...
at a given place have not been less than and 75%, respectively. * A is at least two consecutive days where min temperature is 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 The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
, 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. 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 system A decision support system (DSS) is an information system that supports business or organizational decision-making activities. DSSs serve the management, operations and planning levels of an organization (usually mid and higher management) and ...
s accessible through web sites or smart phones. Several studies have attempted to develop systems for real-time detection via
flow cytometry Flow cytometry (FC) is a technique used to detect and measure the physical and chemical characteristics of a population of cells or particles. In this process, a sample containing cells or particles is suspended in a fluid and injected into the ...
or
microscopy Microscopy is the technical field of using microscopes to view subjects too small to be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of microscopy: optical mic ...
of airborne sporangia collected in air samplers. 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 system A decision support system (DSS) is an information system that supports business or organizational decision-making activities. DSSs serve the management, operations and planning levels of an organization (usually mid and higher management) and ...
s, none have been commercially deployed to date.


Use of fungicides

Fungicide Fungicides are pesticides used to kill parasitic fungi or their spores. Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals, ...
s for the control of potato blight are normally used only in a preventative manner, optionally in conjunction with disease
forecasting Forecasting is the process of making predictions based on past and present data. Later these can be compared with what actually happens. For example, a company might Estimation, estimate their revenue in the next year, then compare it against the ...
. 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 In organic chemistry, a carbamate is a category of organic compounds with the general Chemical formula, formula and Chemical structure, structure , which are formally Derivative (chemistry), derived from carbamic acid (). The term includes orga ...
compounds. A combination of other compounds are recommended for managing metalaxyl-resistant strains. These include mandipropamid, chlorothalonil, fluazinam, triphenyltin,
mancozeb Mancozeb is a dithiocarbamate non-systemic agricultural fungicide with multi-site, protective action on contact. It is a combination of two other dithiocarbamates: maneb and zineb. The mixture controls many fungal diseases in a wide range of fi ...
, and others. In the United States, the Environmental Protection Agency has approved oxathiapiprolin for use against late blight. In African
smallholder A smallholding or smallholder is a small farm operating under a small-scale agriculture model. Definitions vary widely for what constitutes a smallholder or small-scale farm, including factors such as size, food production technique or technolo ...
production fungicide application can be necessary up to once every three days.


In organic production

In the past,
copper(II) sulfate Copper(II) sulfate is an inorganic compound with the chemical formula . It forms hydrates , where ''n'' can range from 1 to 7. The pentahydrate (''n'' = 5), a bright blue crystal, is the most commonly encountered hydrate of copper(II) sulfate, whi ...
solution (called '
bluestone Bluestone is a cultural or commercial name for a number of natural dimension stone, dimension or building stone varieties, including: * basalt in Victoria (Australia), Victoria, Australia, and in New Zealand * diabase, dolerites in Tasmania, ...
') 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 acid Phosphorous acid (or phosphonic acid) is the Compound (chemistry), compound described by the chemical formula, formula . It is diprotic (readily ionizes two protons), not triprotic as might be suggested by its formula. Phosphorous acid is an in ...
s, and
rhamnolipid Rhamnolipids are a class of glycolipid produced by ''Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common Bacterial capsule, encapsulated, Gram-negative bacteria, Gram-negative, Aerobic organism, aerobic–facultative anaerobe, faculta ...
biosurfactant Biosurfactant usually refers to surfactants of microbial origin. Most of the biosurfactants produced by microbes are synthesized extracellularly and many microbes are known to produce biosurfactants in large relative quantities. Some are of commerci ...
s, while sprays containing "beneficial" microbes such as ''
Bacillus subtilis ''Bacillus subtilis'' (), known also as the hay bacillus or grass bacillus, is a gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacill ...
'' or compounds that encourage the plant to produce defensive chemicals (such as knotweed extract) have not performed as well. During the crop year 2008, many of the certified organic potatoes produced in the United Kingdom and certified by the
Soil Association The Soil Association is a British registered charity focused on the effect of agriculture on the environment. It was established in 1946. Their activities include campaigning for local purchasing, public education on nutrition and certificat ...
as organic were sprayed with a copper pesticide to control potato blight. According to the Soil Association, the total copper that can be applied to organic land is /year.


Control of tuber blight

Ridging is often used to reduce tuber contamination by blight. This normally involves piling
soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...
or
mulch A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving soil fertility, fertility and health of the soil, reducing Weed control, weed growth, and enhancing the v ...
around the stems of the potato blight, meaning the
pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...
has farther to travel to get to the tuber. Another approach is to destroy the canopy around five weeks before
harvest Harvesting is the process of collecting plants, animals, or fish (as well as fungi) as food, especially the process of gathering mature crops, and "the harvest" also refers to the collected crops. Reaping is the cutting of grain or pulses fo ...
, using a contact
herbicide Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...
or
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
to burn off the foliage. Eliminating infected foliage reduces the likelihood of tuber infection.


Historical impact

The first recorded instances of the disease were in the United States, in
Philadelphia Philadelphia ( ), colloquially referred to as Philly, is the List of municipalities in Pennsylvania, most populous city in the U.S. state of Pennsylvania and the List of United States cities by population, sixth-most populous city in the Unit ...
and
New York City New York, often called New York City (NYC), is the most populous city in the United States, located at the southern tip of New York State on one of the world's largest natural harbors. The city comprises five boroughs, each coextensive w ...
in early 1843. Winds then spread the spores, and in 1845 it was found from
Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...
to
Nova Scotia Nova Scotia is a Provinces and territories of Canada, province of Canada, located on its east coast. It is one of the three Maritime Canada, Maritime provinces and Population of Canada by province and territory, most populous province in Atlan ...
, and from
Virginia Virginia, officially the Commonwealth of Virginia, is a U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...
to
Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...
. It crossed the
Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...
with a shipment of seed potatoes for Belgian farmers in 1845. The disease being first identified in Europe around
Kortrijk Kortrijk ( , ; or ''Kortrik''; ), sometimes known in English as Courtrai or Courtray ( ), is a Belgian City status in Belgium, city and Municipalities in Belgium, municipality in the Flemish Region, Flemish Provinces of Belgium, province of We ...
, 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. 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 and forced another two million to emigrate. Most commonly referenced is the
Great Irish Famine The Great Famine, also known as the Great Hunger ( ), the Famine and the Irish Potato Famine, was a period of mass starvation and disease in Ireland lasting from 1845 to 1852 that constituted a historical social crisis and had a major impact o ...
, 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 Irish Lumper is a varietal white potato of historic interest. It has been identified as the variety of potato whose widespread cultivation throughout Ireland, prior to the 1840s, is implicated in the Great Famine (Ireland), Irish Great Famin ...
. The lack of
genetic variability Genetic variability is either the presence of, or the generation of, genetic differences. It is defined as "the formation of individuals differing in genotype, or the presence of genotypically different individuals, in contrast to environmentally ...
created a susceptible host population for the organism after the blight strains originating in Chiloé Archipelago replaced earlier potatoes of Peruvian origin in Europe. 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. Since 1941, Eastern Africa has been suffering potato production losses because of strains of ''P. infestans'' from Europe.
France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
,
Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
, the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
, and the
Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
researched ''P. infestans'' as a
biological weapon Biological agents, also known as biological weapons or bioweapons, are pathogens used as weapons. In addition to these living or replicating pathogens, toxins and Toxin#Biotoxins, biotoxins are also included among the bio-agents. More than 1,2 ...
in the 1940s and 1950s. 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.Chemical and Biological Weapons: Possession and Programs Past and Present
, ''James Martin Center for Nonproliferation Studies'',
Middlebury College Middlebury College is a Private university, private Liberal arts colleges in the United States, liberal arts college in Middlebury, Vermont, United States. Founded in 1800 by Congregationalism in the United States, Congregationalists, Middlebury w ...
, 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. 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. 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".()


References


Further reading

* * * * * * * * * * * * *


External links


USAblight A National Web Portal on Late Blight

International Potato Center



EuroBlight a potato blight network in Europe



Organic Alternatives for Late Blight Control in Potatoes, from ATTRA

Google Map of Tomato Potato Blight Daily Risk across NE USA

Species Profile – Late Blight (''Phytophthora infestans'')
National Invasive Species Information Center,
United States National Agricultural Library The United States National Agricultural Library (NAL) is one of the world's largest agricultural research libraries, and serves as a national library of the United States and as the library of the United States Department of Agriculture. Locate ...
. Lists general information and resources for Late Blight.
Continuing education lesson
created by The American Phytopathological Society
entry on Late Blight
by PlantVillage {{Authority control infestans Water mould plant pathogens and diseases Potato diseases Biological agents