| Xiphinema index | |
|---|---|
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Nematoda |
| Class: | Enoplea |
| Order: | Dorylaimida |
| Family: | Longidoridae |
| Genus: | Xiphinema |
| Species: | X. index |
| Binomial name | |
| Xiphinema index Thorne & Allen, 1950 | |
Xiphinema index, the California dagger nematode, is a species of plant-parasitic nematodes.
A major pest of grapes, the California dagger nematode provided the first example of a nematode acting as a vector for a viral plant disease. It has spread to multiple continents where there is viticulture production. [1]
Xiphinema index is a migratory ectoparasite that primarily feeds on the root tips of grapes (Vitis vinifera). The body of a female is around 3 mm long, and the odontostyle is approximately 126 um long. There is a thick cuticle with thin striations across the body. The female has one or two ovaries that are typically paired. Males and females both have dorsally rounded tails that are short. [2] Feeding on a susceptible host causes the root stunting and tip galling. Furthermore, it is a vector of the grapevine fanleaf virus. Other hosts of this parasite include fig, apple, rose, pistachio, as well as several others. [3]
The females of this species lay their eggs in the soil near potential hosts. The first molt does not occur until 24–48 hours after hatching. The following molts occur in six-day intervals after, and complete a life-cycle within 22–27 days. However, a life cycle of several months has also been reported. [3] The nematode can reproduce by parthenogenesis, and thus one female can reproduce an entire population. The nematode survives primarily in the egg stage, although other stages can survive in the soil for up to three years. Xiphinema index causes both mechanical and physiological damage, and may cause terminal swelling and necrosis on the roots of its susceptible hosts. [4]
Xiphinema index has been found to in the following regions: Argentina, Australia, Chile, France, Germany, Greece, Hungary, Iran, Iraq, Italy, North Africa, Portugal, South Africa, Spain, Turkey and USA. In California, it is typically found in the north but can sometimes reach as far south as Kern County. [5] Dagger nematodes can be found in most soil types, and their numbers typically decrease with soil depth. This nematode can be found as deep as 360 cm in the soil. Favorable soil conditions for this nematode are light to medium soil, a pH between 6.5 and 7.5, and relatively warm soil temperatures. [2] California dagger nematode can survive soil temperatures of -11 °C to 35 °C but long term exposure to cold kills the nematode. [6]
Grapevine fanleaf virus (GFLV), the cause of fanleaf degradation, is the most destructive viral disease of grapes worldwide. Xiphinema index was discovered to be a vector of this disease in the 1950s. It causes yellow mosaic and bands on the leaves, and may result in an 80% reduction in fruit set, causing huge economic losses. It is spread by contaminated seed and the grafting of infected rootstocks. [7] [8] In an early experiment, it was shown that California dagger nematodes inoculated with GFLV were still infective after eight months. It is speculated that the two pathogens evolved together, since there is evidence that the presence of GFLV gives a survival advantage to X. index and not other species of nematodes. [9] In a more recent study, it was shown that GFLV persists in juveniles of X. index for over four years, as determined by RT-PCR. [10]
Infected roots should be removed from the vineyard, and a non-host should be grown for several years, if possible. Historically, this pest has been managed by the use of chemical fumigants, such as 1,3-Dichloropropene and Methyl Bromide. There are few post-plant chemical options to manage this pest. These fumigants must be applied deeply in the soil to be effective, as the nematode can reside deeply in the soil and thus resist attempts to eradicate it completely. Rootstocks that are bred for resistance to both GFLV and X. index have proven to be effective at managing the disease. An effective rootstock must be resistant to both the virus and the nematode. Hot water treatments of rootstocks to be planted ensures there will be little chance of the introducing the disease into the field. Preventing the introduction of infected plant or soil material is essential to manage both X. index and GFLV. [2] [3]
Radopholus similis is a species of nematode known commonly as the burrowing nematode. It is a parasite of plants, and it is a pest of many agricultural crops. It is an especially important pest of bananas and citrus, and it can be found on coconut, avocado, coffee, sugarcane, other grasses, and ornamentals. It is a migratory endoparasite of roots, causing lesions that form cankers. Infected plants experience malnutrition.
Xiphinema is a genus of ectoparasitic root nematodes commonly known as dagger nematodes. The genus is of economic importance on grape, strawberry, hops and a few other crops. Major species include X.americanum, X.diversicaudatum, X.index, X.italiae and X.pachtaicum. They can be easily recognized by their long bodies and stylets which are long enough to reach the vascular tissue of plants. Different members of the genus have been shown to induce moderate to large amounts of root damage through root penetration, which in some species results in the formation of galls. They are of agricultural concern because they are vectors of nepoviruses, transferring them during feeding. Efforts to study these nematodes in more detail have proved problematic in some species due to difficulties in maintaining populations in a greenhouse environment.
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.
Aphelenchoides ritzemabosi is a plant pathogenic nematode. It was first scientifically described in 1890 in England. This nematode has a wide host range. Among the most important species affected are Chrysanthemums and strawberries. A. ritzemabosi is a migratory foliar feeding nematode. It can feed both ectoparasitically and endoparasitically, with the later causing the most significant damage. When adequate moisture is present, this nematode enters the leaves and feeds from inside the tissue. Typical damage is characterized by necrotic zones between the veins of the leaves. Its lifecycle is short; only ten days from egg to mature adult. A single female can lay as many as 3,500 eggs. This pest can be difficult to control. Host plant resistance, hot water treatments, and predatory mites are recommended.
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.
Ditylenchus dipsaci is a plant pathogenic nematode that primarily infects onion and garlic. It is commonly known as the stem nematode, the stem and bulb eelworm, or onion bloat. Symptoms of infection include stunted growth, discoloration of bulbs, and swollen stems. D. dipsaci is a migratory endoparasite that has a five-stage lifecycle and the ability to enter into a dormancy stage. D. dipsaci enters through stomata or plant wounds and creates galls or malformations in plant growth. This allows for the entrance of secondary pathogens such as fungi and bacteria. Management of disease is maintained through seed sanitation, heat treatment, crop rotation, and fumigation of fields. D. dipsaci is economically detrimental because infected crops are unmarketable.
Paratylenchus hamatus, the fig pin nematode, is a species of migratory plant endoparasites, that causes lesions on plant roots resulting in symptoms of chlorosis, wilting and ultimately yield losses. They move and feed on different parts of host tissue throughout their life cycle in order to find enough susceptible host tissue to survive and reproduce. A wide range of host plant species are susceptible to the fig pin nematode, including many valuable fruit and vegetable crops such as figs, carrots and celery. They are also commonly found associated with woody perennials in California. P. hamatus inhabits soils in both Europe and North America, and was originally isolated from fig in central California in 1950.
Xiphinema americanum, the American dagger nematode, is a species of plant pathogenic nematodes. 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 viruses, 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.
Xiphinema diversicaudatum is an amphimictic ectoparasitic nematode species. This species has a characteristically long stylet capable of penetrating into a host’s vascular tissue. They have a wide host range with some of the extensively studied ones being strawberry, hops and raspberry, due to their economic importance. The direct root damage caused through penetration near the root tip and formation of galls is a secondary concern when compared with the damage caused by vectoring the arabis mosaic virus. The virus attaches to the interior cuticle lining and can be transferred from infected to uninfected root tissue as the nematode feeds and sheds. Management of this particular nematode relies on nematicides such as 1,3-Dichloropropene (Telone) at 40 gpa.or methyl bromide at 1000 lb/ac to control to 28 in deep.
Tylenchulus semipenetrans is a species of plant pathogenic nematodes and the causal agent of slow decline of citrus. T. semipenetrans is found in most citrus production areas and diverse soil textures worldwide. Their feeding strategy is semi-endoparasitic and has a very narrow host range among commonly grown crops. These nematodes are considered as major plant-parasitic nematode because they can cause 10-30% losses reported on citrus trees. They also parasitize other hosts such as olive, grape, persimmon and lilac. The citrus nematode was first discovered in California in 1913 by J.R. Hodges and was later described and named by Nathan Cobb that year.
Mesocriconema xenoplax is a species of plant parasitic nematodes. Nematodes of this particular species are collectively called ring nematodes.
Arabis mosaic virus is a viral plant pathogen that is known to infect multiple hosts. The pathogen, commonly referred to as ArMV, is from the family Secoviridae, and it causes yellow dwarf of raspberry and is one of the causes of mosaic of rhubarb. Arabis mosaic virus infects multiple hosts, including strawberries, hops, hemp, grape, geraniums, raspberries, sugar beets, celery, horseradish, lilac, peach, and lettuces.
Grapevine fanleaf virus (GFLV) is a plant pathogenic virus of the family Secoviridae. It infects grapevines, causing chlorosis of the leaves and lowering the fruit quality. Because of its effect on grape yield, GFLV is a pathogen of commercial importance. It is transmitted via a nematode vector, Xiphinema index. This nematode acquires the virus through feeding on roots of an infected plant, and passes it on in the same manner.
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.
Strawberry foliar nematode, or strawberry crimp nematode, is a disease caused by Aphelenchoides fragariae, a plant pathogenic nematode. it is common in strawberries and ornamental plants and can greatly affect plant yield and appearance, resulting in a loss of millions of dollars of revenue. Symptoms used to diagnose the disease are angular, water soaked lesions and necrotic blotches. Aphelenchoides fragariae is the nematode pathogen that causes the disease. Its biological cycle includes four life stages, three of which are juvenile. The nematode can undergo multiple life cycles in one growing season when favorable conditions are present. They can infect the crowns, runners, foliage, and new buds of the plant via stylet penetration or through the stomata. The best management practices for this disease are sanitation, prevention of induction of the pathogen to the environment, and planting clean seed or starter plants.
Grapevine yellows (GY) are diseases associated to phytoplasmas that occur in many grape growing areas worldwide and are of still increasing significance. The most important grapevine yellows is flavescence dorée.
Grapevine virus A (GVA) is a moderately common genetic virus that affects Vitis vinifera and American Vitis grapevine species throughout the world and can be fatal if not treated. Grapevine virus A is in the family Betaflexiviridae and genus Vitivirus. The common name for this virus is grapevine closterovirus. Common symptoms in infected grapevines include stem pitting. Although there is a treatment available to cure infected grapevines, it is not one hundred percent effective, so preventative measures are the best solution to the virus. Every inhabited continent on the globe has had breakouts of grapevine closterovirus due to the complex genetic makeup of the virus. Grapevine virus A has a single-stranded RNA genome, which is similar to that of Grapevine virus B. There are multiple strains of the virus that vary both molecularly and biologically which account for the slightly different symptoms exhibited by infected plants.
Planococcus ficus, commonly known as the vine mealybug, is a species of mealybug, belonging to the family Pseudococcidae, native to tropical and subtropical regions. The vine mealybug is found in Europe, Northern Africa, Southern Africa, the Americas, and the Middle East. The vine mealybug is invasive to weedy plants in many different regions of the world.