Pratylenchus Alleni
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''Pratylenchus alleni'' is a migratory endoparasitic nematode, living inside of plant roots and feeding on parenchyma cells in the root cortex. ''P. alleni'' is an obligate biotroph, meaning it must have a living host in order to survive. Due to their incredibly broad host range, ''
Pratylenchus ''Pratylenchus'' is a genus of nematodes known commonly as lesion nematodes.Crow, W. TAmaryllis lesion nematode, ''Pratylenchus hippeastri''.EENY-546. University of Florida IFAS. 2012. They are parasitism, parasitic on plants and are responsible ...
'' species fall third in total economic impact, finishing just behind cyst nematodes (''
Heterodera ''Heterodera'' is a genus of nematodes in the family Heteroderidae. Members of the genus are obligate parasites and different species attack different crops, often causing great economic damage. The genus is unique among nematode genera because ...
&
Globodera Potato root nematodes or potato cyst nematodes (PCN) are 1-mm long roundworms belonging to the genus ''Globodera'', which comprises around 12 species. They live on the roots of plants of the family Solanaceae, such as potatoes and tomatoes. PCN c ...
'') and root knot nematodes (''
Meloidogyne Root-knot nematodes are plant-parasitic nematodes from the genus ''Meloidogyne''. They exist in soil in areas with hot climates or short winters. About 2000 species of plants worldwide are susceptible to infection by root-knot nematodes and they ...
)''. In
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 ...
, it was isolated for the first time in 2011 in a
soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean. Soy is a staple crop, the world's most grown legume, and an important animal feed. Soy is a key source o ...
field.


History

''Pratylenchus alleni'', also referred to as the Root Lesion Nematode, was initially found in the U.S. while infesting nine different varieties of soybeans within a single field in El Dorado,
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 ...
.


Distribution

''Pratylenchus alleni'' has been found all across the globe in almost every cool, temperate and tropical climates and growing conditions. Although it is more frequently found in
Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
,
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 ...
, and
North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating Direction (geometry), direction or geography. Etymology T ...
, Central and
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.


Morphology

Male and female Root Lesion Nematodes have the same stylet length of about 14 μm long with well-developed basal knobs. Body length of adult males and females ranges from .33mm - .44mm. Also, they have two annuli, a round spermatheca and this species has both males and females present. Female ovaries have a short single row of oocytes on each end with two rows of oocytes in the middle. Their vulval body diam is slightly shorter than their post-vulval uterine sac with their vulva to anus difference measuring 3 times that of their tail length. Males are very similar to female morphology, with an arrangement of spermatocytes in double or triple rows. Distinguishing characteristics of ''P. alleni'' include a bluntly rounded labial region, lateral fields with four lines, subcylindrical tail with a terminus that is smooth and rounded. Their matrix code is: A1, B2, C2, D2, E3, F2, G2, H1, I3, J1, K1 which is determine using tabular and dichotomous keys based on their morphological characters. Their lateral fields, stylet length, excretory pore and vulva position, post-vulval uterine sac length and number of annuli on tail all serve as distinguishing factors between ''P. alleni'' and other closely related species ''P. flakkensis, P. neobrachyurus''.


Life cycle & reproduction

Similar to all
nematodes The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (he ...
who are parasitic to plants, ''P. alleni'' have 6 stages within their life cycle: egg, juvenile 1–4, and adult. Both males and females are required for reproduction to occur. Adult females lay eggs within the root, or in the soil near the root surface. These eggs can be laid singularly or in small groups. The first molt happens within the egg, so at the time of hatching, ''P. alleni'' juveniles are in their second juvenile stage (J2). They are able to enter the root and infect throughout all of their life stages, minus the egg and J1 stages, as they are not yet mobile. As a migratory endoparasite, these pests move freely throughout the root to feed and reproduce, destroying host cells and tissue as they move intracellularly. They remain vermiform throughout their life cycle, and can be found within the roots, or within soil after their host dies and can no longer support them. From egg to adult, the cycle is anywhere from 3–8 weeks, depending on temperature, moisture and other environmental conditions.


Host parasite relationship

As an obligate biotroph, ''P. alleni'' needs a living host in order to survive. It can feed on and impact several different plants, all with different economic value – some food production crops and others of aesthetic appeal. For example, it has been recorded on
Chrysanthemum Chrysanthemums ( ), sometimes called mums or chrysanths, are flowering plants in the Asteraceae family. They are native to East Asia and northeastern Europe. Most species originate from East Asia, and the center of diversity is in China. Co ...
in
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
;
raspberry The raspberry is the edible fruit of several plant species in the genus ''Rubus'' of the Rosaceae, rose family, most of which are in the subgenus ''Rubus#Modern classification, Idaeobatus''. The name also applies to these plants themselves. Ras ...
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Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...
;
vetch ''Vicia'' is a genus of over 240 species of flowering plants that are part of the legume family (Fabaceae), and which are commonly known as vetches. Member species are native to Europe, North America, South America, Asia and Africa. Some other g ...
and
chickpea The chickpea or chick pea (''Cicer arietinum'') is an annual plant, annual legume of the family (biology), family Fabaceae, subfamily Faboideae, cultivated for its edible seeds. Its different types are variously known as gram," Bengal gram, ga ...
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Turkey Turkey, officially the Republic of Türkiye, is a country mainly located in Anatolia in West Asia, with a relatively small part called East Thrace in Southeast Europe. It borders the Black Sea to the north; Georgia (country), Georgia, Armen ...
; and soybean,
cotton Cotton (), first recorded in ancient India, is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure ...
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wheat Wheat is a group of wild and crop domestication, domesticated Poaceae, grasses of the genus ''Triticum'' (). They are Agriculture, cultivated for their cereal grains, which are staple foods around the world. Well-known Taxonomy of wheat, whe ...
in
Arkansas Arkansas ( ) is a landlocked state in the West South Central region of the Southern United States. It borders Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, Texas to the southwest, and Oklahoma ...
, USA. It has a very broad host range and can be found on several additional hosts including
corn Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout Poaceae, grass that produces cereal grain. It was domesticated by indigenous peoples of Mexico, indigenous peoples in southern Mexico about 9,000 years ago ...
,
tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...
, haricot bean,
potatoes 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 ...
,
legumes Legumes are plants in the pea family Fabaceae (or Leguminosae), or the fruit or seeds of such plants. When used as a dry grain for human consumption, the seeds are also called pulses. Legumes are grown agriculturally, primarily for human consu ...
,
bananas A banana is an elongated, edible fruit – berry (botany), botanically a berry – produced by several kinds of large treelike herbaceous flowering plants in the genus ''Musa (genus), Musa''. In some countries, cooking bananas are called pla ...
, etc. Some plants are impacted more than others, for instance, the damage threshold of ''P. alleni'' on soybeans is 14 nematodes/100cc or 1 cm³ soil. Their vermiform shape and mobility allow them to enter the root and move freely throughout, feeding on the parenchyma tissue of the root cortex. This feeding causes a reduction of plant growth, less lateral roots, loss of cytoplasm in infected cells, redish brown necrotized lesions, as well as predisposing the damaged roots to fungi and bacteria that can initiate a secondary infection. Using their stylet, ''Pratylenchus'' nematodes secrete wall degrading enzymes that help to break down cell walls and allow for more ease of movement. Their movement intracellularly breaks down the tissue, losing turgor pressure, increasing nucleus size and eventually destroying cells along their path of movement. This wounding also allows for other secondary pathogens, such as bacteria and fungi, to invade and cause additional infection.


Management

Many management strategies are used for most ''Pratylenchus'' species, not just ''P. alleni.'' Chemically based
nematicide A nematicide is a type of chemical pesticide used to kill plant- parasitic nematodes. Nematicides have tended to be broad-spectrum toxicants possessing high volatility or other properties promoting migration through the soil. Aldicarb (Temik), a ...
s were traditionally the most commonly used, but over time some have been pulled from the market due to environmental restrictions and concerns, as well as the cost of re-registration of a product. Crop rotation, cover crops, resistant plant varieties, nematicidal plants, soil amendments, fallow periods, soil solarization, thermotherapy, irrigation management and others are all commonly used to suppress reproduction, reduce nematode populations, and minimize their damage. Biological solutions, such as predatory fungi and bacteria have also been studied, and in many cases have been used commercially through seed treatments and other nematicides. Sanitation and chemical nematicides are some of the most widely used, but the best control method is to prevent their initial infestation and plant non-host crops. Complete eradication is not very attainable, and control of populations can be very difficult when most commonly used agricultural practices can assist in movement of the nematode between fields through the movement of infested soil and plants.


References

{{Taxonbar, from=Q7238808 alleni Agricultural pest nematodes Soybean diseases Endoparasites Nematodes described in 1961