|Potato cyst nematode (Eel worms)|
|Nematode cysts on potato roots|
|Genus:|| 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 cause growth retardation and, at very high population densities, damage to the roots and early senescence of plants. The nematode is not indigenous to Europe but originates from the Andes. Fields are free from PCN until an introduction occurs, after which the typical patches, or hotspots, occur on the farmland. These patches can become full field infestations when unchecked. Yield reductions can average up to 60% at high population densities.
The eggs hatch in the presence of Solanoeclepine A, a substance secreted by the roots of host plants otherwise known as root exudates. The nematodes hatch when they grow into a second-stage juvenile (J2). At this stage, the J2 nematodes find host cells to feed off of. The potato cyst nematodes are endoparasites meaning they go completely into the root to feed. Access to the root cells is gained through piercing through the cell wall using the nematode’s stylet. After a feeding tube has been established, a syncytium begins to form through the breakdown of multiple cell walls adjacent to each other. J2 nematodes continue to feed until they grow into third-stage juveniles (J3), then fourth-stage juveniles (J4), and finally reach the adult stage. The shape of the J3 females begins to appear more like a sac as the female grows into a J4 nematode. At the J4 stage, the body of the female nematode lies outside of the root while the head remains inside the cell. During this stage, the male nematodes become motile again and are then able to fertilize the female nematodes leading to embryos developing inside the female body. Once the female is fertilized, the female dies and leaves a protective cyst containing 200-500 eggs. [ citation needed ]Once the cysts detach from the original hosts, they remain in the soil until they find another suitable host beginning the cycle again. Cyst nematodes are monocyclic because they have one life cycle per season. Potato cyst nematodes can be detected by their patchy distribution in the field. The specific distribution is caused by the limited spread of these nematodes. Most potato cyst nematodes don’t migrate very far across a field because of their feeding patterns. Both susceptible and resistant potato varieties will suffer from growth retardation at low and medium populations densities. At very high population densities mechanical damage of the root system will occur. The female individuals swell up and appear as cysts on the surface of the roots, each containing up to 400 eggs. In temperate zones only one generation per year will occur. In the Mediterranean countries sometimes a second generation is reported. Cysts can then also be found on the skin of the tubers. Each year without host a certain fraction of the eggs will hatch (spontaneous hatch). The eggs can survive for up to 20 years inside these cysts.
The speed of spread of the nematodes from field to field can be reduced by cleaning equipment of possibly infested soil before changing location and by using only certified PCN-free seed tubers. If possible, ask for seed potatoes grown on fields which were declared free of the potato cyst nematode using an AMI-intensive soil sampling scheme (currently only available in The Netherlands). Pesticides can be used, but they will not get a field free of nematodes. They will increase yields and are only profitable at high population densities, when the financial profit of the extra yield will surpass the cost of the pesticide application. Crop rotation with at least 6 years between planting of a susceptible crop is an effective means to reduce nematode population densities to below damage threshold. However, the best way to manage potato cyst nematodes is the use of (partial) resistant potato varieties. During the last 10 years[ when? ] a number of varieties have been developed which can keep both potato cyst nematode species below damage and detection threshold, without the use of pesticides. Other methods of pest control include nematicides such as fosthiazate. Fosthiazate is applied directly to the soil in specific time intervals. The level of toxicity is important to consider when applying and depends on the manufacturer and the specific instructions of application. The use of certified disease free seed will also assure that potato cyst nematodes are not present due to planting infected tubers. Soil testing for potato cyst nematodes is also crucial in keeping track of the prevalence of the nematodes. Controlling the quantity of the nematodes allows the prevention of an epidemic. Lastly, resistance to potato cyst nematode has been found in Solanum acaule . The downside is that Solanum acaule is a wild potato species containing high glycoalkaloid content making it toxic for consumers.
Potato cyst nematodes have the ability to cause a large scale devastation in crops due to the massive amounts of nematode embryos in each cyst. Many continents across the world such as Australia, North America, Asia, Europe, and Africa have had many epidemics of potato cyst nematodes that continue to persist year after year.Potato cyst nematodes are important economically due to the fact that they reduce the crop yield exceedingly. A species of potato cyst nematodes called pale cyst nematodes (Globodera pallida) are able to cause 80% yield loss in a potato field if left untreated. On a more global scale, the Australian potato industry is worth about AUD$500 million yearly which equates to $340 million U.S. dollars. Other countries that are mass producers of potatoes are China with 88.9 million metric tons produced annually, India with 45.34 million metric tons produced annually, and Russia with 30.20 million metric tons produced annually. The continual spread of potato cyst nematodes alludes more economical depression in many major potato producing countries.
The official recommendations and requirements for crop rotation vary between countries.
Northern root-knot nematode is a species of vegetable pathogens which produces tiny galls on around 550 crop and weed species. They invade root tissue after birth. Females are able to lay up to 1,000 eggs at a time in a large egg mass. By surviving harsh winters, they can survive in cold climates.
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 plants worldwide are susceptible to infection by root-knot nematodes and they cause approximately 5% of global crop loss. Root-knot nematode larvae infect plant roots, causing the development of root-knot galls that drain the plant's photosynthate and nutrients. Infection of young plants may be lethal, while infection of mature plants causes decreased yield.
The soybean cyst nematode (SCN), Heterodera glycines, is the most devastating pest to soybean crop yields in the U.S., targeting the roots of soybean and other legume plants. When infection is severe SCNs cause stunting, yellowing, impaired canopy development, and yield loss. The symptoms caused by SCNs can go easily unrecognized by farmers - in some cases there are no warning symptoms before a loss of 40% of the yield. Due to the slight stunting and yellowing, many farmers may mistake these symptoms as environmental problems when in fact they are SCNs. Due to the fact that soybean cyst nematodes can only move a few centimeters in the soil by themselves, they mostly are spread via tillage or plant transplants. This area of infection will look patchy and nonuniform making diagnosis more difficult for farmers. They can be seen in the roots of summer soybean plants if the roots are taken out very carefully and gently washed with water. The egg masses should be seen as bright white or yellow "pearls" on the roots. The later the roots are pulled the harder it will be to diagnose due to the SCNs female dying and turning a much darker color, forming a "cyst". The best way to know if a field is infected by soybean cyst nematodes is to take a soil sample to a nematologist.
Rotylenchulus reniformis, the reniform nematode, is a species of parasitic nematode of plants with a worldwide distribution in the tropical and subtropical regions.
Meloidogyne arenaria is a species of plant pathogenic nematodes. This nematode is also known as the peanut root knot nematode. The word "Meloidogyne" is derived from two Greek words that mean "apple-shaped" and "female". The peanut root knot nematode, M. arenaria is one of the "major" Meloidogyne species because of its worldwide economic importance. M. arenaria is a predominant nematode species in the United States attacking peanut in Alabama, Florida, Georgia, and Texas. The most damaging nematode species for peanut in the USA is M. arenaria race 1 and losses can exceed 50% in severely infested fields. Among the several Meloidogyne species that have been characterized, M. arenaria is the most variable both morphologically and cytologically. In 1949, two races of this nematode had been identified, race 1 which reproduces on peanut and race 2 which cannot do so. However, in a recent study, three races were described. López-Pérez et al (2011) had also studied populations of M. arenaria race 2, which reproduces on tomato plants carrying the Mi gene and race 3, which reproduces on both resistant pepper and tomato.
Pratylenchus penetrans is a species of nematode in the genus Pratylenchus, the lesion nematodes. It occurs in temperate regions worldwide, regions between the subtropics and the polar circles. It is an animal that inhabits the roots of a wide variety of plants and results in necrotic lesions on the roots. Symptoms of P. penetrans make it hard to distinguish from other plant pathogens; only an assay of soil can conclusively diagnose a nematode problem in the field. P. penetrans is physically very similar to other nematode species, but is characterized by its highly distinctive mouthpiece. P. penetrans uses its highly modified mouth organs to rupture the outer surface of subterranean plant root structures. It will then enter into the root interior and feed on the plant tissue inside. P. penetrans is considered to be a crop parasite and farmers will often treat their soil with various pesticides in an attempt to eliminate the damage caused by an infestation. In doing this, farmers will also eliminate many of the beneficial soil fauna, which will lead to an overall degradation of soil quality in the future. Alternative, more environmentally sustainable methods to control P. penetrans populations may be possible in certain regions.
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Globodera pallida is a species of nematode in the family Heteroderidae. It is well known as a plant pathogen, especially of potatoes. It is "one of the most economically important plant parasitic nematodes," causing major crop losses, and is a model organism used to study the biology of cyst nematodes. Its common names include potato cyst nematode, white potato cyst nematode, pale potato cyst nematode, potato root eelworm, golden nematode, and pale cyst nematode.
Globodera rostochiensis, commonly known as the golden nematode, golden eelworm or yellow potato cyst nematode, is a plant pathogenic nematode. It is a pest of plants in the family Solanaceae, primarily infesting potatoes and tomatoes, as well as a variety of other root crops.
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Heterodera sacchari, the sugarcane cyst nematode, mitotic parthenogenic sedentary endoparasitic nematode. This plant-parasitic nematode infects the roots of sugarcane, and the female nematode eventually becomes a thick-walled cyst filled with eggs. Aboveground symptoms are species specific and are similar to those caused by other Heterodera species. Symptoms include: stunted and chlorotic plants, and reduced root growth. Seedlings may be killed in heavily infested soils.
Tobacco rattle virus (TRV) is a pathogenic plant virus. Over 400 species of plants from 50 families are susceptible to infection.
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Pratylenchus is a genus of nematodes known commonly as lesion nematodes. They are parasitic on plants and are responsible for root lesion disease on many taxa of host plants in temperate regions around the world. Lesion nematodes are migratory endoparasites that feed and reproduce in the root and move around, unlike the cyst or root-knot nematodes, which may stay in one place. They usually only feed on the cortex of the root. Species are distinguished primarily by the morphology of the stylets.
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