Xiphinema americanum
Encyclopedia
Xiphinema americanum is a plant pathogenic nematode
. It is one of many species that belongs to the genus Xiphinema
. It was first described by N. A. Cobb
in 1913, who found it on both sides of the United States
on the roots of grass, corn, and citrus trees. Not only is Xiphinema americanum known to vector plant virus
es, but also X. americanum has been referred to as "the most destructive plant parasitic nematode in America", and one of the four major nematode pests in the Southeastern United States.
odontostyle which is used for deep penetration of root
tips with its spear-like stylet. The odontostyle is connected to the lining of the cheilostome by a folded membrane called the "guiding ring". The guiding ring is attached to a flanged odontophore.
Females: The body is usually in an "open C" conformation. The shape of the body tapers towards the extremities. The two rings of the odontophore are located 3 μm apart. The Xiphinema americanum esophagus
is dorylaimoid with an enlarged posterior portion that occupies roughly 1/3 of its total length. The esophagus contains a muscular bulb which is 80 μm long and 20 μm wide. The valve between the esophagus and the intestine is amorphous. The vulva is 46-54% of the total body length, and is located equatorially with a transverse slit shape, with the vagina having a diameter of 1/3 of the body diameter. The ovaries normally occur in pairs, and are amphidelphic and relexed. The prerectum of X. americanum measures 120-140 μm long, with a rectum that is roughly the same length as the body diameter at the anus. The tail contains 2-3 pairs of caudal pores, is conoid, and curves dorsally with a subacute terminus.
Males: The males have a similar overall configuration as the females, but are slightly smaller in length. Males of X. americanum, however, are rarely found in nature. The male has diorchic testes that are connected to the cloaca
, with one anterior branch and one posterior branch. It is common to find more coil in the posterior region. The males also have paired spicules but lack a gubernaculum
and bursa.
stages. The eggs of X. americanum are laid directly into the soil
in water films, and are not associated with an egg mass. No molt occurs within the egg, which means that the first stage juvenile is the stage that enters the soil. Before becoming sexually mature
adults, the X. americanum nematodes undergo three to four juvenile stages with a molt occurring between each.
Measurements of the functional and replacement odontostyles allows for the determination of the current stage in development. Compounding the issue of determining the life cycle of X. americanum is their difficulty with being grown in culture
or greenhouse
conditions. It has been suggested that this is due to X. americanum's sensitivity to moisture tension, temperature fluctuation, physical handling, or oxygen deprivation.
Field evidence taken over a 2 year observation period indicates that X. americanum are most likely k-selected; they most likely have a long life span and a low reproduction rate. Unpublished results have shown greenhouse observations of X. americanum to develop from egg to adult in 7 months. Other results have suggested that X. americanum can live as long as 3-5 years.
Reproduction by fertilization from a male is rare if not nonexistent due to the lack of male X. americanum individuals, and therefore females reproduce parthogenetically
. All of the stages of X. americanum occur in the soil, with no particular stage as an important survival stage. In places with low winter temperatures, however, the egg is the primary survival structure.
. The most common plant hosts infected
by X. americanum are common weeds and grasses, strawberries
, soybeans, forest trees (spruce
, pine
, etc.), perennial orchards, and grapes
. This broad host range is due to the genetic diversity
within the X. americanum species. For a complete list of the host range of X. americanum visit the Nemaplex Host Database.
. The states with the highest population of the American Dagger Nematode are Arkansas
, California
, Pennsylvania
, Rhode Island
and Virginia
. Other countries where X. americanum is found include Australia, Belize, Brazil, Chile, Guatemala, India, Japan, Korea Democratic People's Republic, Korea Republic, Mexico, New Zealand,Pakistan, Panama, South Africa, Sri Lanka, Uruguay, and areas of the Caribbean as well.
This species of nematode is also found to be sensitive to soil pH
, and they are found most frequently in soils with a pH of 6.0 or higher.
. These nematodes are migratory ectoparasites and all of the life stages of the American Dagger Nematode feed at the root tips of plants. Since it is a migratory ectoparasite, they remain outside the root or other feeding areas and feed on epidermal cells
or on cells deeper in the root. This ectoparasitism allows the nematode to move freely to different hosts throughout its life cycle. This nematode is not considered to be an obligate parasite
because it can survive in a saprophytic stage within plant debris.
Once the nematode arrives at a root tip, it feeds by puncturing several successive layers of the plant's cells with its odontostyle; while penetrating, the nematode secretes enzymes
that result in cell hypertrophy
and thickening. The nematode is then able to begin extracting the cell's cytoplasm
. The feeding period of X. americanum can last anywhere from several hours to several days, with the average being around 36 hours at each feeding site along the plant's roots. While feeding, it is common for the nematodes to remain still with their bodies either outstretched or curled, and following the feeding period they move slowly along the length of the root with their stylet remaining protruded and in search of a new feeding site. Unlike some species of nematodes, the observation of food passing into the gut of X. americanum is not seen. Although the nematodes are non-specific in their Host Range, they generally feed on plants that are in poorer condition for a shorter amount of time.
that plants exhibit in response to the pathogenicity
of Xiphinema americanum are similar to those of other migratory ectoparasitic nematodes of roots. It is common to see poor growth and or stunting
of the plant, yellowing or wilting
of the foliage, and reduced root systems which can include root necrosis
, lack of feeder or secondary roots, and occasional tufts of stubby rootlets.
Young, shortleaved yellow pine trees
with moderate swelling of roots with clusters of short, stubby branches were the first demonstration of X. americanum pathogenicity in 1955. X. americanum can also cause severe effects on foliage, sometimes causing chlorosis and complete defoliation as seen on Guatemalan coffee trees. The dagger nematode causes the devitalization of root tips and overall root death when they feed at the root tips and root sides of strawberry plants. Reddish-brown lesions
that turn black and necrotic with time result on the sites of feeding, and result in reduced root systems and stunted tops.
Xiphinema americanum is listed as a C-rated pest in California due to its wide host range of California crops, according to The California Department of Food and Agriculture. Due to X. americanum's difficulty in maintaining high populations in frequently tilled soils (see Control), the dagger nematode is mainly an economic problem on biennial
and permanent crops rather than annual crops (except for damage to emerging seedlings).
of various plant viruses including tomato ringspot nepovirus
(TomRSV), tobacco ringspot nepovirus
(TRSV), peach rosette mosaic nepovirus
(PRMV), and cherry rasp leaf nepovirus
(CRLV).
TobRSV is a widespread nepovirus
in annual crops in North America that infects tobacco, soybean, blueberry, apple, ash, autumn crocus, blackberry, cherry, dogwood, elderberry, grapevine, spearmint, and in Wisconsin has an economically important impact on cucurbits
.
TomRSV is another nepovirus transmitted by X. americanum, and is generally a problem with perennial plants including tomato, apple, grapevine, raspberry, strawberry, birdsfoot-trefoil, cucumber, dogwood, elderberry, hydrangeas, orchids, and red currants.
Apple, cherry, and peach trees on the Pacific coast states of the United States are infected by CRLV.
PRMV causes substantial damage to Prunus spp., grapevine, and blueberry in the Great Lakes area.
Much like the broad host range of X. americanum, the 4 nepovirus
es transmitted by this nematode do as well. They also have the capability of dissemination in wind-blown seeds as well as remaining harbored in natural reservoirs including weeds.
In parallel tests, TomRSV has been shown to transmit more efficiently than TRSV. Advanced techniques have been used to located where nepoviruses reside in X. americanum individuals. Primarily, the viruses reside in the regions of the stylet extension, the anterior esophageal lumen, and rarely in the esophageal bulb. TRSV has been shown to prefer the areas of the stylet extension and anterior esophageal lumen, whereas the TomRSV is found mainly in the triradiate lumen of the esophageal bulb. The different locations of viral binding sites for TRSV and TomRSV account for the capability of dual transmission of both viruses, because the different viruses aren't competing for binding sites. TRSV particles can be liberated into the plant during feeding by the dorsal and subventral gland secretions. TomRSV is mainly liberated by the secretions of the subventral glands due to its location in the triradiate lumen. These facts may account for the differences in the experimentally determined transformation efficiency between TomRSV (100%), and TRSV (75% or less). Previous work attempting to identify virus binding sites and release was impossible without the development of immunoflourescent labeling.
generally remove up to 95% of the nematodes in soil, however the 5% that remain can reproduce asexually
and the viruses that they carry can still infect the roots of young plants. Therefore, to completely manage the nematodes nematicides should be used, and additionally no plants should be planted within that particular region for at least a 2 year period. At the end of this 2 year period the nematodes should be completely ridden.
The spraying of nematicides also causes plants to release allelopathic chemicals. These chemicals then kill the nematodes by active suppression because they are toxic to the nematode. Crop rotation is another form of control for X. americanum and it has been shown that certain host plants may deny the nematode population an adequate food source for reproduction, and thus greatly reduce its population in the soil. This is termed passive suppression.
X. americanum can only travel via run-off
and in damp soil, therefore if soils are kept dry enough the nematodes can be localized and quarantined
.
Additionally, if soil is tilled
frequently, X. americanum will likely not be in high enough of a population density to cause any noticeable symptoms in its hosts. There is also evidence of X. americanum resistance
and "tolerance" seen in certain species of grapes that appeared to be better adapted
to the parasite.
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
. It is one of many species that belongs to the genus Xiphinema
Xiphinema
Xiphinema is a genus of plant-parasitic roundworms.- List of species :* Xiphinema abrantinum Roca & Pereira, 1991.* Xiphinema aceri Chizhov & al., 1986.* Xiphinema aequum Roca & Lamberti, 1988....
. It was first described by N. A. Cobb
Nathan Cobb
Nathan Augustus Cobb is known as "the father of nematology in the United States".He provided the foundations for nematode taxonomy and described over 1000 different nematode species...
in 1913, who found it on both sides of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
on the roots of grass, corn, and citrus trees. Not only is Xiphinema americanum known to vector plant virus
Plant virus
Plant viruses are viruses that affect plants. Like all other viruses, plant viruses are obligate intracellular parasites that do not have the molecular machinery to replicate without a host. Plant viruses are pathogenic to higher plants...
es, but also X. americanum has been referred to as "the most destructive plant parasitic nematode in America", and one of the four major nematode pests in the Southeastern United States.
Morphology and anatomy
The length of the adult Xiphinema americanum ranges from 1.3 to 3.0 millimeters. The dagger nematode is characterized by a 100 μmMicrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
odontostyle which is used for deep penetration of root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
tips with its spear-like stylet. The odontostyle is connected to the lining of the cheilostome by a folded membrane called the "guiding ring". The guiding ring is attached to a flanged odontophore.
Females: The body is usually in an "open C" conformation. The shape of the body tapers towards the extremities. The two rings of the odontophore are located 3 μm apart. The Xiphinema americanum esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
is dorylaimoid with an enlarged posterior portion that occupies roughly 1/3 of its total length. The esophagus contains a muscular bulb which is 80 μm long and 20 μm wide. The valve between the esophagus and the intestine is amorphous. The vulva is 46-54% of the total body length, and is located equatorially with a transverse slit shape, with the vagina having a diameter of 1/3 of the body diameter. The ovaries normally occur in pairs, and are amphidelphic and relexed. The prerectum of X. americanum measures 120-140 μm long, with a rectum that is roughly the same length as the body diameter at the anus. The tail contains 2-3 pairs of caudal pores, is conoid, and curves dorsally with a subacute terminus.
Males: The males have a similar overall configuration as the females, but are slightly smaller in length. Males of X. americanum, however, are rarely found in nature. The male has diorchic testes that are connected to the cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...
, with one anterior branch and one posterior branch. It is common to find more coil in the posterior region. The males also have paired spicules but lack a gubernaculum
Gubernaculum
The paired Gubernacula are embryonic structures which begin as undifferentiated mesenchyme attaching to the caudal end of the gonads .-Function during development:...
and bursa.
Life cycle
Identifying Xiphinema americanum as a separate species has been a difficult task because of overlapping morphological aspects; however, differences in the life cycles of X. americanum may differentiate them from other Xiphinema species. Findings may also suggest that two subgroups of X. americanum should be made due to the finding of either 3 or 4 juvenileJuvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
stages. The eggs of X. americanum are laid directly into the soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
in water films, and are not associated with an egg mass. No molt occurs within the egg, which means that the first stage juvenile is the stage that enters the soil. Before becoming sexually mature
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
adults, the X. americanum nematodes undergo three to four juvenile stages with a molt occurring between each.
Measurements of the functional and replacement odontostyles allows for the determination of the current stage in development. Compounding the issue of determining the life cycle of X. americanum is their difficulty with being grown in culture
Microbiological culture
A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions. Microbial cultures are used to determine the type of organism, its abundance in the sample being tested,...
or greenhouse
Greenhouse
A greenhouse is a building in which plants are grown. These structures range in size from small sheds to very large buildings...
conditions. It has been suggested that this is due to X. americanum's sensitivity to moisture tension, temperature fluctuation, physical handling, or oxygen deprivation.
Field evidence taken over a 2 year observation period indicates that X. americanum are most likely k-selected; they most likely have a long life span and a low reproduction rate. Unpublished results have shown greenhouse observations of X. americanum to develop from egg to adult in 7 months. Other results have suggested that X. americanum can live as long as 3-5 years.
Reproduction by fertilization from a male is rare if not nonexistent due to the lack of male X. americanum individuals, and therefore females reproduce parthogenetically
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...
. All of the stages of X. americanum occur in the soil, with no particular stage as an important survival stage. In places with low winter temperatures, however, the egg is the primary survival structure.
Host range
X. americanum is a virtually non-specific plant nematode, causing it to have over one hundred different plant hostsHost (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
. The most common plant hosts infected
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
by X. americanum are common weeds and grasses, strawberries
Strawberry
Fragaria is a genus of flowering plants in the rose family, Rosaceae, commonly known as strawberries for their edible fruits. Although it is commonly thought that strawberries get their name from straw being used as a mulch in cultivating the plants, the etymology of the word is uncertain. There...
, soybeans, forest trees (spruce
Spruce
A spruce is a tree of the genus Picea , a genus of about 35 species of coniferous evergreen trees in the Family Pinaceae, found in the northern temperate and boreal regions of the earth. Spruces are large trees, from tall when mature, and can be distinguished by their whorled branches and conical...
, pine
Pine
Pines are trees in the genus Pinus ,in the family Pinaceae. They make up the monotypic subfamily Pinoideae. There are about 115 species of pine, although different authorities accept between 105 and 125 species.-Etymology:...
, etc.), perennial orchards, and grapes
Grape
A grape is a non-climacteric fruit, specifically a berry, that grows on the perennial and deciduous woody vines of the genus Vitis. Grapes can be eaten raw or they can be used for making jam, juice, jelly, vinegar, wine, grape seed extracts, raisins, molasses and grape seed oil. Grapes are also...
. This broad host range is due to the genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....
within the X. americanum species. For a complete list of the host range of X. americanum visit the Nemaplex Host Database.
Distribution
X. americanum are found widely throughout most of the world and are found on all of the continents, except for Antarctica. The region with the most predominant amount of X. americanum is thought to be the Eastern United StatesEastern United States
The Eastern United States, the American East, or simply the East is traditionally defined as the states east of the Mississippi River. The first two tiers of states west of the Mississippi have traditionally been considered part of the West, but can be included in the East today; usually in...
. The states with the highest population of the American Dagger Nematode are Arkansas
Arkansas
Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, Pennsylvania
Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...
, Rhode Island
Rhode Island
The state of Rhode Island and Providence Plantations, more commonly referred to as Rhode Island , is a state in the New England region of the United States. It is the smallest U.S. state by area...
and Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
. Other countries where X. americanum is found include Australia, Belize, Brazil, Chile, Guatemala, India, Japan, Korea Democratic People's Republic, Korea Republic, Mexico, New Zealand,Pakistan, Panama, South Africa, Sri Lanka, Uruguay, and areas of the Caribbean as well.
This species of nematode is also found to be sensitive to soil pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
, and they are found most frequently in soils with a pH of 6.0 or higher.
Feeding habits
X. americanum are plant parasites that live entirely in the soil and are attracted to young, growing roots due to source-sink dynamicsSource-sink dynamics
Source-sink dynamics is a theoretical model used by ecologists to describe how variation in habitat quality may affect the population growth or decline of organisms....
. These nematodes are migratory ectoparasites and all of the life stages of the American Dagger Nematode feed at the root tips of plants. Since it is a migratory ectoparasite, they remain outside the root or other feeding areas and feed on epidermal cells
Epidermis (botany)
The epidermis is a single-layered group of cells that covers plants' leaves, flowers, roots and stems. It forms a boundary between the plant and the external environment. The epidermis serves several functions, it protects against water loss, regulates gas exchange, secretes metabolic compounds,...
or on cells deeper in the root. This ectoparasitism allows the nematode to move freely to different hosts throughout its life cycle. This nematode is not considered to be an obligate parasite
Obligate parasite
An obligate parasite is a parasitic organism that cannot complete its life cycle without dependence on its host.-See also:*Obligate intracellular parasite*Parasitism*Parasitic plant*Facultative parasite...
because it can survive in a saprophytic stage within plant debris.
Once the nematode arrives at a root tip, it feeds by puncturing several successive layers of the plant's cells with its odontostyle; while penetrating, the nematode secretes enzymes
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
that result in cell hypertrophy
Hypertrophy
Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It should be distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number...
and thickening. The nematode is then able to begin extracting the cell's cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
. The feeding period of X. americanum can last anywhere from several hours to several days, with the average being around 36 hours at each feeding site along the plant's roots. While feeding, it is common for the nematodes to remain still with their bodies either outstretched or curled, and following the feeding period they move slowly along the length of the root with their stylet remaining protruded and in search of a new feeding site. Unlike some species of nematodes, the observation of food passing into the gut of X. americanum is not seen. Although the nematodes are non-specific in their Host Range, they generally feed on plants that are in poorer condition for a shorter amount of time.
Symptoms and economic importance
The symptomsSymptom
A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality...
that plants exhibit in response to the pathogenicity
Pathogenicity
Pathogenicity is the ability of a pathogen to produce an infectious disease in an organism.It is often used interchangeably with the term "virulence", although virulence is used more specifically to describe the relative degree of damage done by a pathogen, or the degree of pathogenicity caused by...
of Xiphinema americanum are similar to those of other migratory ectoparasitic nematodes of roots. It is common to see poor growth and or stunting
Stunt (botany)
In botany and agriculture, stunting describes a plant disease that results in dwarfing and loss of vigor. It may be caused by infectious or noninfectious means.-Infectious:A stunt caused by infectious means usually is too late to cure.* Nematodes...
of the plant, yellowing or wilting
Wilting
Wilting refers to the loss of rigidity of non-woody parts of plants. This occurs when the turgor pressure in non-lignified plant cells falls towards zero, as a result of diminished water in the cells...
of the foliage, and reduced root systems which can include root necrosis
Necrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...
, lack of feeder or secondary roots, and occasional tufts of stubby rootlets.
Young, shortleaved yellow pine trees
Yellow pine
Yellow pine may refer to the following:*Certain pines in the subgenus Pinus subgenus Pinus:**In American forestry, a term for several closely related species of pine with yellow tinted wood, including the Southern Yellow Pines , and the non-Southern yellow pines and several others...
with moderate swelling of roots with clusters of short, stubby branches were the first demonstration of X. americanum pathogenicity in 1955. X. americanum can also cause severe effects on foliage, sometimes causing chlorosis and complete defoliation as seen on Guatemalan coffee trees. The dagger nematode causes the devitalization of root tips and overall root death when they feed at the root tips and root sides of strawberry plants. Reddish-brown lesions
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
that turn black and necrotic with time result on the sites of feeding, and result in reduced root systems and stunted tops.
Xiphinema americanum is listed as a C-rated pest in California due to its wide host range of California crops, according to The California Department of Food and Agriculture. Due to X. americanum's difficulty in maintaining high populations in frequently tilled soils (see Control), the dagger nematode is mainly an economic problem on biennial
Biennial plant
A biennial plant is a flowering plant that takes two years to complete its biological lifecycle. In the first year the plant grows leaves, stems, and roots , then it enters a period of dormancy over the colder months. Usually the stem remains very short and the leaves are low to the ground, forming...
and permanent crops rather than annual crops (except for damage to emerging seedlings).
Viral transmission
The nematode Xiphinema americanum is an important transmitterTransmission of plant viruses
-Problems associated with viral transmission:Viruses are known to infect both plant cells and animal cells. Since viruses are obligate intracellular parasites they must develop direct methods of transmission, between hosts, in order to survive...
of various plant viruses including tomato ringspot nepovirus
Tomato ringspot virus
Tomato ringspot virus is a plant pathogenic virus of the family Comoviridae. It affects tomatoes.-External links:* Descriptions of Plant Viruses: **...
(TomRSV), tobacco ringspot nepovirus
Tobacco ringspot virus
Tobacco ringspot virus is a plant pathogenic virus in the plant virus family Comoviridae. It is the type species of the Comoviridae Genus Nepovirus. Nepoviruses are be transmitted between plants by nematodes...
(TRSV), peach rosette mosaic nepovirus
Peach rosette mosaic virus
Peach rosette mosaic virus is a plant pathogenic virus of the family Comoviridae.-External links:**...
(PRMV), and cherry rasp leaf nepovirus
Cherry rasp leaf virus
Cherry rasp leaf virus is a plant pathogenic virus of the order Picornavirales, family Secoviridae, subfamily Comovirinae, genus Cheravirus.- Symptoms :...
(CRLV).
TobRSV is a widespread nepovirus
Nepovirus
Nepoviruses or nematode transmitted polyhedral viruses, are a genus of plant viruses of the family Secoviridae and subfamily Comovirinae...
in annual crops in North America that infects tobacco, soybean, blueberry, apple, ash, autumn crocus, blackberry, cherry, dogwood, elderberry, grapevine, spearmint, and in Wisconsin has an economically important impact on cucurbits
Cucurbitaceae
The plant family Cucurbitaceae consists of various squashes, melons, and gourds, including crops such as cucumber, pumpkins, luffas, and watermelons...
.
TomRSV is another nepovirus transmitted by X. americanum, and is generally a problem with perennial plants including tomato, apple, grapevine, raspberry, strawberry, birdsfoot-trefoil, cucumber, dogwood, elderberry, hydrangeas, orchids, and red currants.
Apple, cherry, and peach trees on the Pacific coast states of the United States are infected by CRLV.
PRMV causes substantial damage to Prunus spp., grapevine, and blueberry in the Great Lakes area.
Much like the broad host range of X. americanum, the 4 nepovirus
Nepovirus
Nepoviruses or nematode transmitted polyhedral viruses, are a genus of plant viruses of the family Secoviridae and subfamily Comovirinae...
es transmitted by this nematode do as well. They also have the capability of dissemination in wind-blown seeds as well as remaining harbored in natural reservoirs including weeds.
In parallel tests, TomRSV has been shown to transmit more efficiently than TRSV. Advanced techniques have been used to located where nepoviruses reside in X. americanum individuals. Primarily, the viruses reside in the regions of the stylet extension, the anterior esophageal lumen, and rarely in the esophageal bulb. TRSV has been shown to prefer the areas of the stylet extension and anterior esophageal lumen, whereas the TomRSV is found mainly in the triradiate lumen of the esophageal bulb. The different locations of viral binding sites for TRSV and TomRSV account for the capability of dual transmission of both viruses, because the different viruses aren't competing for binding sites. TRSV particles can be liberated into the plant during feeding by the dorsal and subventral gland secretions. TomRSV is mainly liberated by the secretions of the subventral glands due to its location in the triradiate lumen. These facts may account for the differences in the experimentally determined transformation efficiency between TomRSV (100%), and TRSV (75% or less). Previous work attempting to identify virus binding sites and release was impossible without the development of immunoflourescent labeling.
Control
Control of the American Dagger Nematode presents problems because, as a vector for viruses, X. americanum is hard to completely remove. NematicidesNematicide
A nematicide is a type of chemical pesticide used to kill parasitic nematodes.One common nematicide is obtained from neem cake, the residue obtained after cold-pressing the fruit and kernels of the neem tree. Known by several names in the world, the tree was first cultivated in India in ancient...
generally remove up to 95% of the nematodes in soil, however the 5% that remain can reproduce asexually
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
and the viruses that they carry can still infect the roots of young plants. Therefore, to completely manage the nematodes nematicides should be used, and additionally no plants should be planted within that particular region for at least a 2 year period. At the end of this 2 year period the nematodes should be completely ridden.
The spraying of nematicides also causes plants to release allelopathic chemicals. These chemicals then kill the nematodes by active suppression because they are toxic to the nematode. Crop rotation is another form of control for X. americanum and it has been shown that certain host plants may deny the nematode population an adequate food source for reproduction, and thus greatly reduce its population in the soil. This is termed passive suppression.
X. americanum can only travel via run-off
Surface runoff
Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...
and in damp soil, therefore if soils are kept dry enough the nematodes can be localized and quarantined
Quarantine
Quarantine is compulsory isolation, typically to contain the spread of something considered dangerous, often but not always disease. The word comes from the Italian quarantena, meaning forty-day period....
.
Additionally, if soil is tilled
Tillage
Tillage is the agricultural preparation of the soil by mechanical agitation of various types, such as digging, stirring, and overturning. Examples of human-powered tilling methods using hand tools include shovelling, picking, mattock work, hoeing, and raking...
frequently, X. americanum will likely not be in high enough of a population density to cause any noticeable symptoms in its hosts. There is also evidence of X. americanum resistance
Plant disease resistance
Plant disease resistance is crucial to the reliable production of food, and it provides significant reductions in agricultural use of fuel, land, water and other inputs. There are numerous examples of devastating plant disease impacts , as well as recurrent severe plant disease issues...
and "tolerance" seen in certain species of grapes that appeared to be better adapted
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
to the parasite.