Anguina tritici (wheat seed gall nematode)
- Summary of Invasiveness
- Taxonomic Tree
- Distribution Table
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Seedborne Aspects
- Pathway Causes
- Pathway Vectors
- Plant Trade
- Impact Summary
- Risk and Impact Factors
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Anguina tritici (Steinbuch, 1799) Chitwood, 1935
Preferred Common Name
- wheat seed gall nematode
Other Scientific Names
- Anguillula scandens Schneider, 1866
- Anguillula tritici (Steinbuch, 1799) Grube, 1849
- Anguillulina scandens (Schneider) Goodey, 1932
- Anguillulina tritici (Steinbuch, 1799) Gervais & Van Beneden, 1859
- Anguina tritici (Steinbuch, 1799) Gervais & van Beneden, 1859
- Rhabditis tritici (Steinbuch, 1799) Dujardin, 1845
- Tylenchus scandens (Schneider, 1866) Cobb, 1890
- Tylenchus tritici (Steinbuch, 1799) Bastian, 1865
- Vibrio tritici Steinbuch, 1799
International Common Names
- English: cockle wheat; earcockles; eelworm disease; purples; wheat cockle nematode; wheat nematode; wheatgall nematode
- Spanish: anguillado del trigo; anguilulosis del trigo; falso tizon del trigo
- French: anguillule du ble; anguillulose du ble nielle; nielle du ble
Local Common Names
- Denmark: hvedeal; hvedegallnematod
- Germany: Gichtkoerner des Weizens; Kaulbrand; Radekrankheit des Weizens; radenkrankheit; Weizen-Aelchen
- India: tundu
- Italy: Anguillula del frumento
- Japan: Komugi-tubu-sentyu; Tubu-sentyubyo
- Netherlands: Tarweaaltje
- Sweden: froegallnematod pa vete
- Turkey: bugday gal nematodu
- ANGUTR (Anguina tritici)
- RHATTR (Rhabditis tritici)
Summary of InvasivenessTop of page
Anguina tritici, commonly referred to as wheat seed gall nematode, is the cause of ear-cockle disease. It was the first plant-parasitic nematode to be described in the scientific literature in 1743. Its host range includes wheat, triticale, rye, and related grasses; the primary host is wheat. Ear cockle in the past was reported in all major wheat growing areas. However, physical and mechanical methods for separating infected galls from seed have eradicated the nematode from the western hemisphere. It remains a problem in several countries in the Near and Middle East, the Asian Subcontinent and Eastern Europe, most likely due to poor awareness and lack of campaigns for establishing clean seed. A. tritici is on the U.S. Pests of Economic and Environmental Importance List, and on the ‘Harmful Organism Lists’ for Argentina, Brazil, Chile, Colombia, Ecuador, Egypt, Guatemala, Indonesia, Israel, Madagascar, Namibia, Nepal, New Zealand, Paraguay, Peru, South Africa, Taiwan, Thailand, Timor-Leste and Uruguay.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Nematoda
- Class: Secernentea
- Order: Tylenchida
- Family: Anguinidae
- Genus: Anguina
- Species: Anguina tritici
DescriptionTop of page
(After Goodey, 1932):
Females: L = 3-5 mm; a = 25-30; b = 20-25; c = 32-50; V = 90-94.
Males: L = 2-2.5 mm; a = 25-29; b = 12-13; c = 25-28.
Second stage juveniles: L = 0.8-0.95 mm; width = 15-20 µm.
Eggs: 85 x 38 µm (mean).
(After Filipjev and Schuurmans Stekhoven, 1941):
Females: L = 4.1-5.2 mm; a = 21; b = 19; c = 30; V = 88-97; spear = 9-11 µm.
Males: L = 1.9-2.5 mm; a = 30; b = 13; c = 14; spear = 9-11 µm.
First-stage juveniles: L = 0.5-0.6 mm; a = 42; b = 4.5.
Second-stage juveniles: L = 0.8-1.0 mm.
Eggs: 85 x 39 µm (73-140 x 33-63 µm).
(After Swarup and Gupta, 1971):
Eggs (n = 25); L = 75.6-102.3 µm (87.1 ± 7.8 µm). Breadth = 34.9-53.5 µm (43.8 ± 5.3 µm).
Second-stage juveniles: (n = 20): L = 0.75-0.79 mm (0.77 mm); a = 47-59 (54); b = 4.0-6.3 (4.5); c = 23-28 (26); stylet = 10 µm.
Third-stage female (n = 4): L = 1.11-1.55 mm (1.26 mm); a = 28-40 (32); b = 9.3-10.2 (9.8); c = 20.0-22.2 (21.1).
Third-stage male (n = 6): L = 1.10-1.23 mm (1.11 mm); a = 26-42 (36); b = 6.4-8.2 (7.6); c = 10.2-13.4 (12.8).
Fourth-stage female (n=12); L = 1.45-1.92 mm (1.86); a = 21.0-26.5 (22.4); b = 9.6-18.4 (13.2); c = 20.0-35.4 (32.3).
Fourth-stage male (n = 2): L = 1.76, 1.82 mm; a = 25.4, 29.1; b = 7.5, 9.4; c = 15.0, 20.0.
Adult female (n=22); L = 2.64-4.36 mm (3.24 ± 0.37 mm); a = 13.2-22.2 (17.98 ± 8.10); b = 9.8-19.40 (13.98 ± 2.50); c = 24.0-63.0 (36.4 ± 9.12); V = 70.4-89.8 (80.7 ± 6.84).
Adult male (n = 18); L = 2.04-2.40 mm (2.19 ± 0.32 mm); a = 21.2-30.0 (26.58 ± 2.05); b = 6.30-11.0 (9.29 ± 0.91); c = 17.0-23.8 (19.70 ± 1.55); T = 66.70-81.40 (75.40 ± 3.18).
No type specimens extant.
Annules very fine, usually visible only in oesophageal region; lateral fields with four or more fine incisures, in adults visible only on young specimens. Lip region low and flattened, slightly offset; lips visible as six raised, radial ridges. Procorpus of oesophagus swollen but constricted at junction with median bulb. Oesophageal glands forming a roughly pyriform bulb but varying in shape and sometimes showing irregular lobes, not overlapping intestine; cardia small. Tail conoid, tapered to an obtuse or rounded tip.
Chromosomes: 2n = 38 (Triantaphyllou and Hirschmann, 1966).
Female: Body obese, spirally coiled ventrally when relaxed by heat. Isthmus of oesophagus sometimes swollen posteriorly ('storage gland' of Thorne, 1949) then offset from glandular region by a deep constriction. Anterior branch of genital tract greatly developed; ovary usually with two or more flexures, with many oöcytes arranged about a rachis and ending distally in a cap cell (according to Triantaphyllou and Hirschmann (1966) the latter is a terminal epithelial cell). Spermatheca ± pyriform, its broader end separated from oviduct by a sphincter, its narrower end merging into uterus. Posterior genital branch a simple post-vulval sac. Vulval lips prominent. Several eggs may be present in uterus at one time.
Male: Body sometimes curved dorsally when heat relaxed, i.e. ventral surface outermost. Testis with one or two flexures; spermatocytes arranged about a rachis, ending distally in a cap cell. Vas deferens about 200 µm long, separated from testis by a constriction. Spicules paired, stout, arcuate, each having two ventral ridges running from tip to widest part: the head rolled or folded ventrally. Gubernaculum simple, trough-like. Bursa arises just anterior to spicules and ends just short of tail-tip.
DistributionTop of page
There is evidence that this species is becoming extinct or rare in regions where it has been reported in the past. Therefore, older records should be treated with caution.
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.Last updated: 23 Nov 2020
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|-Jammu and Kashmir||Present|
|-Madhya Pradesh||Present, Widespread|
|Israel||Present, Few occurrences|
|Saudi Arabia||Present, Localized|
|-Russian Far East||Present|
|Serbia and Montenegro||Present|
|Slovenia||Present||Original citation: Urek and Širca (2003)|
|United States||Absent, Formerly present||Absent, formerly present - based on changes in agricultural practices|
|-Georgia||Absent, Formerly present|
|-Maryland||Absent, Formerly present|
|-North Carolina||Absent, Formerly present|
|-South Carolina||Absent, Formerly present|
|-Virginia||Absent, Formerly present|
|-West Virginia||Absent, Formerly present|
|Brazil||Absent, Formerly present|
Risk of IntroductionTop of page
Risk Criteria Category
ECONOMIC IMPORTANCE Moderate
SEEDBORNE INCIDENCE Moderate
SEED TRANSMITTED Yes
SEED TREATMENT No
OVERALL RISK Moderate
Notes on Phytosanitary Risk
A. tritici should be considered a low-level risk because it is easy to detect and control and has been eliminated from many grain-growing areas. Selective quarantine should be established in parts of the world where it is not under control.
HabitatTop of page
A. tritici thrives in cool conditions in most climates where wheat is grown. The favoured micro-habitat for A. tritici comprises the seed galls where all stages are protected from hostile environmental factors. It also lives in soil, either in or out of galls, and in dry seed storage.
Habitat ListTop of page
|Terrestrial||Managed||Cultivated / agricultural land||Principal habitat||Harmful (pest or invasive)|
Hosts/Species AffectedTop of page
A. tritici is highly specialized with a narrow host range. Significant multiplication only occurs on wheat or closely related plants. Many common grasses have been exposed to A. tritici; most have been shown to be non-hosts (Leukel, 1957).
In addition to the hosts listed in the table, Alopecurus monspeliensis and Lolium temulentum (Dahiya and Bhatti, 1980), Holcus lanatus and Phleum pratensis (Filipjev and Schuurmans Stekhoven, 1941), and Triticum monococcum (Southey, 1972) are also reported as hosts of A. tritici.
Host Plants and Other Plants AffectedTop of page
|Avena sativa (oats)||Poaceae||Other|
|Hordeum vulgare (barley)||Poaceae||Other|
|Secale cereale (rye)||Poaceae||Main|
|Triticum aestivum (wheat)||Poaceae||Main|
|Triticum spelta (spelt)||Poaceae||Main|
|Triticum turgidum (durum wheat)||Poaceae||Other|
Growth StagesTop of page
SymptomsTop of page
The absence of symptoms does not mean absence of A. tritici (Thorne, 1949). Slight elevations occur on the upper leaf surface with indentations on the lower side. Other symptoms include wrinkling, twisting, curling of the margins towards the midrib, distortion, buckling, swelling and bulging. A tight spiral coil evolves, and dwarfing, loss of colour or a mottled, yellowed appearance and stem bending may also occur (Byars, 1920; Leukel, 1924). In severe infection, the entire above-ground plant is distorted to some degree and a disease problem is usually obvious.
Wheat heads are reduced with glumes protruding at an abnormal angle exposing the galls to view. This does not occur in rye heads.
Young galls are short-thick, smooth, light to dark green, turning brown to black with age, 3.5-4.5 mm long and 2-3 mm wide. Rye galls are small, buff-coloured and longer than wide, 2-4.5 mm long by 1-2.5 mm wide (Byars, 1920; Leukel, 1924).
List of Symptoms/SignsTop of page
|Inflorescence / galls|
|Inflorescence / twisting and distortion|
|Leaves / abnormal colours|
|Leaves / abnormal forms|
|Leaves / leaves rolled or folded|
|Seeds / galls|
|Stems / stunting or rosetting|
|Stems / witches broom|
|Whole plant / dwarfing|
Biology and EcologyTop of page
Several weeks elapse in moist soil before the gall is softened enough to release the juveniles. It takes 2-9 days for juveniles to reach a plant (Leukel, 1924); the first plant encountered is invaded. Horizontal and vertical migration do not exceed 20-30 cm (Leukel, 1957) and 7-19 cm (Limber, 1980), respectively. A film of moisture must be present on the invaded plant to allow nematode movement. Juveniles swim up the stem and enter the leaves or leaf sheath; they then migrate to the growing point where they feed ectoparasitically.
When the floral organs appear, the staminate tissue is invaded followed by the carpellate tissue. Juveniles feed ectoparasitically until floral tissue develops, when gall formation is stimulated. Galls arise from undifferentiated carpellate tissue. Juveniles develop into males or females in the gall (fewer than 25 per gall), and thousands of eggs are deposited. One female can deposit up to 2000 eggs (Southey, 1972). Mature females form tight coils, become quiescent, and die following oviposition. Juveniles entering leaves produce a whitish gall and leaf symptoms.
The entire life cycle of A. tritici is completed in about 113 days; however, the life cycle has been reported to last up to 164 days in India (Swarup and Gupta, 1971). It is not uncommon for juveniles to leave the gall in autumn and seek new plants for overwintering or to overwinter in soil (Maggenti, 1981). Some juveniles leave galls in the autumn and overwinter in the leaf sheaths of host plants (Leukel, 1957). Juveniles enter a state of anhydrobiosis in dry storage. The water content in the nematodes is reduced from the normal level of 45-50% to 5%, lipid droplets become crinkled and indented and the body becomes tightly coiled (Bird and Buttrose, 1974).
The nematodes invade the leaves and leaf sheaths of emergent seedlings and also the developing floral parts. In the final stages of attack, they modify the seed into nematode-infected galls in the floral tissue.
Juveniles in the gall range in number from 3600-32,400 in India (Thorne, 1961). The number of females and males in galls ranged from 3-37 and 1-41, respectively (Christie, 1959). A minimum population of 10,000 juveniles/kg soil is essential for development of ear-cockle. Disease intensity is greatest when nematode galls are placed in soil at a depth of 2-6 cm than when placed deeper (Luc et al., 2005).
A. tritici has survived up to 35 years in dry storage (Thorne, 1961). Juveniles do not survive more than 1 year in field soil (Norton, 1978). Some juveniles survive in the faeces of rodents, sheep, frogs, salamanders and goldfish (Norton, 1978).
Spores of a pathogen, such as Dilophosphora alopecuri, may be carried into the floral tissue on the cuticle of A. tritici. However, in most cases the disease organism is detected inside the gall with A. tritici.
When the entire gall is filled with pathogen spores, the nematodes are eliminated by competition. One disease is traded for another with no real economic gain.
The following diseases are associated with A. tritici: Corynebacterium michiganense pv. tritici [Rathayibacter tritici] on Polypogon monspeliensis (Paruthi et al., 1989); Clavibacter tritici [R. tritici] on barley (Bhatti et al., 1978) and wheat (Swarup and Singh, 1962); and Dilophosphora alopecuri (Poinar, 1983), D. graminus (Filipjev and Schuurmans Stekhoven, 1941), Neovossia indica [Tilletia indica] (Paruthi and Bhatti, 1980), Sclerophthora macrospora (Paruthi et al., 1992), Tilletia foetida [T. laevis] (Mathur and Misra, 1961), Ustilago nuda [U. segetum var. nuda] (Beniwal et al., 1991), Sitophilus oryzae, Tribolium castaneum and T. confusum on wheat (Nath et al., 1984).
Yellow ear-rot, or 'tundu', is a nematode-vectored bacterial disease commonly associated with ear-cockle. The disease is caused by the association of A. tritici with R. tritici.
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
Notes on Natural EnemiesTop of page
There are few reports concerning natural enemies of A. tritici. The nematodes, Arthrobotrys oligospora (Filipjev and Schuurmans Stekhoven, 1941), Mononchoides fortidens and M. longicaudatus (Bilgrami and Jairajpur, 1989) all reduce numbers of A. tritici. The fungi, Dilophosphora graminis (Filipjev and Schuurmans Stekhoven, 1941) and Tilletia tritici (Thorne, 1961) cause the nematodes in galls to die as a result of competition rather than by attack.
Means of Movement and DispersalTop of page
The principal means of dispersion is by wheat seed containing infected galls in commerce and by sowing infected galls in fields. In a survey of grain markets in Haryana, India, 34.17% of wheat samples were found to be contaminated with seed galls caused by A. tritici; the incidence of ear-cockle and tundu disease (caused by association with Rathayibacter tritici) on wheat earheads was 2.85%. Maximum contamination (63.2%) was found in wheat variety C306 and minimum (12.3%) in the dwarf variety WL711 (Paruthi and Bhatti, 1985). The level of R. tritici infection of A. tritici galls has been reported at 20.4% (Paruthi et al., 1989).
Other means of spread include straw from an infected crop, rainfall and flooding, natural migration (20-30 cm), and cow, sheep, sparrow, pigeon and goldfinch manure. A. tritici is also spread by animal feet; farm implements and machines; and by wind (Leukel, 1957).
Seedborne AspectsTop of page
In a survey of grain markets in Haryana, India, 34.17% of wheat samples were found to be contaminated with seed galls caused by A. tritici; the incidence of ear-cockle and tundu disease (caused in association with Rathayibacter tritici) on wheat earheads was 2.85%. Maximum contamination (63.2%) was found in wheat variety C306 and minimum (12.3%) in the dwarf variety WL711 (Paruthi and Bhatti, 1985). The level of R. tritici infection of A. tritici galls has been reported at 20.4% (Paruthi et al., 1989). In surveyed regions in Iran (Ahmadi and Akhiyani, 2001), 21.71% of fields were infested with A. tritici. The mean of infected heads was 5.82% and crop loss was 0.3% of the total yield (1444 tonnes of wheat). The range in size of the nematode galls and the population of A. tritici secondary juveniles in collected wheat samples were determined for each area. The nematode galls ranged from 2.4-5.3 x 1.5-4.2 mm. The maximum and minimum numbers of second stage juveniles were 40,250 and 4625, respectively. A survey of head sterility in Syria during the harvest of 1996 included 120 samples representing 30 barley fields in northern Syria (Khatib et al., 2000). Incidence of head sterility varied in the surveyed fields between 9.6 and 57% (average 23.4%). Estimated grain losses ranged from 0.1 to 43.2% (average loss of 11.2%). Preliminary results showed that head sterility prevails in short, normal and tall plants at rather similar levels, i.e. 21.9, 23.3 and 31.1%, respectively. Furthermore, the results showed a correlation between head sterility and the presence of seed gall nematodes.
The life cycle of A. tritici is fully synchronized with the wheat plant. The second-stage larvae take a few days to reach the embryonic growing point of the wheat seed. They continue to increase in numbers at the growing point until 45 days after inoculation. The larvae start penetrating the flower primordia from the 68th day and the developmental stages are discernible from the 70th day onwards. The total life cycle (from second stage to second stage) takes 103 days (Gokte and Swarup, 1987).
The relationship between A. tritici and R. tritici has been shown in inoculation experiments. Symptoms of ear-cockle and tundu were produced by inoculations with nematode seed galls or unsterilized larvae. The bacterial disease, however, did not appear when R. tritici was inoculated alone in the soil or on the wheat growing point (Gupta and Swarup, 1972).
Effect on Seed Quality
Ears of wheat completely infected with tundu (R. tritici) or ear-cockle (A. tritici) showed 100% loss in grain formation. Partially cockled ears resulted in 53.4 and 51.0% grain loss on the basis of number and weight, respectively, whereas ears partially attacked with tundu had grain losses of 68.7 and 77.2%. Other quality characters (colour, appearance and degree of acceptability) of grains obtained from ears partially attacked with tundu were also inferior to those from cockled and healthy ears (Paruthi et al., 1987).
The size of the galls caused by A. tritici on wheat is directly correlated with the number of adult nematodes inside the galls. A maximum of 283 were recorded from a single gall, but the usual number is 10 to 80/gall (Midha and Swarup, 1974).
Ear-cockles are the only source of perpetuation of the disease. The principal means of dispersion of the nematode is by wheat seed containing infected galls and by planting infected galls in fields (Luc et al., 2005). Secondary stage juveniles of A. tritici emerge from the galls, penetrate the shoots of the emerging seedling and then migrate upwards between the leaf sheaves. Larvae around the growing point are mechanically carried to the developing ears as culms elongate, where they enter into the flowers (Neergaard, 1977).
In Syria, an experiment was conducted in pots under field conditions to investigate the relationship between inoculum density and infection level of seed-gall nematode and barley yield losses. Inoculation was done at sowing with 125, 250, 500 and 1000 juveniles/100 g soil. A non-inoculated system was used as a control. Two cultivars of the six-rowed barley (Rihan 3 and Furat 1), and two of the two-rowed barley (Tadmor and Zanbaka) were used. The lowest inoculum density of the nematode (125 juveniles/100 g soil) influenced infection level and grain loss. Severity of infection increased with every increase in inoculum density. However, yield reduction slightly increased with increases in inoculum density (26.1, 27.5, 31.6 and 36.8% for 125, 250, 500 and 1000 juveniles/100 g soil), respectively. Results also showed that incidence of infection varied significantly among the cultivars tested, but Rihan 3 was less affected (22.8%) compared to Furat 1, Tadmor and Zanbaka (36.7, 41 and 47.7%, respectively) (Al-Zainab et al., 2001).
Early investigations of the disinfection of contaminated seed produced varying results. Marcinowski (1909), Byars (1919) and Sommerville (1919) reported that contaminated seed could not be thoroughly disinfested without injuring the wheat seed. Chu (1945) obtained good results with corrosive sublimate.
Various methods have been used to separate nematode galls from seed lots including fanning, screening and flotation in water. However, none of these methods are as effective as a brine treatment in which sound wheat kernels sink while galls, light kernels and debris float (Suryanarayana and Mukhopadhaya, 1971).
Hot-water treatment of contaminated wheat seed is also effective in the removal of nematode galls from seed lots (Suryanarayana and Mukhopadhaya, 1971). Marcinowski (1909) demonstrated that galls in a seed lot could be destroyed by keeping the mixture in water at 54-56°C for 10-12 minutes. Pre-soaking seeds before the hot-water treatment has also been advocated (Byars, 1919; Chu, 1945).
Jones et al. (1938) developed an indented cylinder machine which separated oval wheat seeds from globular nematode galls; the device was claimed to be 98% effective in removing seed galls. Chu (1945) also designed a machine to separate nematode galls from healthy grain.
Microwave irradiation significantly decreased the mycoflora of soaked (from 8 and 10 seconds onwards) and unsoaked (from 10 and 12 seconds onwards), healthy and cockled seeds, respectively. Mortality of A. tritici juveniles inside soaked and unsoaked cockles was significantly greater from 10- and 14-second-long treatments, respectively. The seed germination decreased (P = 0.05) from 16 seconds onwards (Khan and Hayat, 1999).
Seed Health Test
Examine seed lots for the presence of nematode galls that are brown-black and lack the brush and embryo marking of normal kernels. They can be distinguished from ergots or sclerotia by the release of motile larvae when wetted (Wiese, 1987).
Pathway CausesTop of page
Pathway VectorsTop of page
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Bulbs/Tubers/Corms/Rhizomes||adults; eggs; juveniles||Yes||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Flowers/Inflorescences/Cones/Calyx||adults; eggs; juveniles||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Leaves||adults; eggs; juveniles||Yes||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Seedlings/Micropropagated plants||adults; eggs; juveniles||Yes||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Stems (above ground)/Shoots/Trunks/Branches||adults; eggs; juveniles||Yes||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|True seeds (inc. grain)||adults; eggs; juveniles||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Plant parts not known to carry the pest in trade/transport|
|Fruits (inc. pods)|
|Growing medium accompanying plants|
Impact SummaryTop of page
ImpactTop of page
A. tritici has been practically eliminated from grainfields in Europe by using clean seed and crop rotation. Up to 100% losses have been reported in wheat, with wheat grain ears totally infected (Paruthi et al., 1987). Reddy (1983) also reported high losses (90%) in wheat seedlings; and 8.5% of sowed wheat seeds galled, resulting in 69% loss. In China, A. tritici causes an annual market reduction in wheat (Chu, 1945). The conversion of wheat grains to galls caused losses of 6.54 million rupees in India (Sakhuja et al., 1990). Paruthi and Bhatti (1988) reported 23-48% losses and a market price reduction when 5% of wheat seed were galled and flour which contained 2% seed galls was also unacceptable. Losses of 50 and 65% were reported in wheat and rye, respectively (Leukel, 1957), and 52% losses occurred through infestation of the inoculated wheat field market (Paruthi and Bhatti, 1981). These losses were recorded in the absence of control measures, before the introduction of phytosanitary programmes.
Risk and Impact FactorsTop of page
- Invasive in its native range
- Proved invasive outside its native range
- Has a broad native range
- Long lived
- Has propagules that can remain viable for more than one year
- Host damage
- Negatively impacts agriculture
- Negatively impacts animal health
- Negatively impacts livelihoods
- Damages animal/plant products
- Negatively impacts trade/international relations
- Pest and disease transmission
- Interaction with other invasive species
- Parasitism (incl. parasitoid)
DiagnosisTop of page
A. tritici was detected in cereal seed by direct visual inspection as well as wash-filter, freezing-blotter, embryo, seed-gall nematode and growing-on tests (Asaad and Abang, 2009).
Three assay methods are used to detect the presence of A. tritici.
Dissection: a scalpel and tweezers are used to dissect seeds and release nematodes in water.
Salt: this is used to assay dry lots of seed for A. tritici. Seeds are poured into a 20% salt solution, stirred vigorously, and the debris skimmed from the surface and examined under the microscope for galls.
Baermann funnel method: a 9 cm coarse wire screen disc is placed into a 15 cm funnel. Water is added to the funnel just above the support disc and a paper tissue is added to the funnel. The seed subsample is poured to just below the rim of the funnel and water is added until the funnel is full. The funnel is left undisturbed for 24 hours. Water from the funnel is drawn into a 50 ml centrifuge tube and the residue from the tube is pipetted onto a microscope slide after 30 minutes for diagnosis.
Detection and InspectionTop of page
Similarities to Other Species/ConditionsTop of page
Symptoms of A. tritici attack are similar to aphid, drought and Hessian fly [Mayetiola destructor] damage. Some plant disease galls resemble nematode galls and may erroneously indicate the presence of A. tritici. Smutted galls crush easily into a black powder, ergot sclerotia (caused by Claviceps purpurea) produce elongated fungal bodies and Clavibacter tritici [Rathayibacter tritici] produces bright yellow, slimy exudations on the spike (Thorne, 1949). Cockle seed is black and hairy.
A. tritici is closely related to A. funesta and Subanguina wevelli. The morphological separation of these three species is difficult (Society of Nematologists, undated). PCR-RFLP diagnostic techniques have facilitated the separation of these three species (Powers et al., 2001). Highly sensitive real-time PCR techniques have been developed to simultaneously identify and distinguish A. tritici, A. funesta, A. agrostis and A. pacificae (Li et al., 2015).
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Ear-cockles are the only source for perpetuation of the disease and their removal from contaminated seed lots can completely eradicate the disease (Luc et al., 2005). A. tritici has been eliminated, or reduced to a minimal number of infestations, in Europe and the USA by seed cleaning, crop rotation and fallow (Brown, 1987).
Cultural Control and Sanitary Methods
Salt brine method (Byars, 1920; Leukel, 1957): seed (1 peck per treatment) is poured into a salt solution (8 lbs salt in 5 gallons water) and stirred vigorously. Sound galls sink, and debris and galls float to the surface. The galls and debris are skimmed from the surface and steamed, boiled or chemically treated to kill the nematodes. The salt solution is drained into another container and the cleaned seed is rinsed several times in fresh water to remove salt and then spread in thin layers on a clean surface to dry. The cleaned seed is ready to sow when dry. It is important that the seed is washed two or three times in plain water after brine treatment to remove salt particles which may impair germination.
Crop rotation or fallow:
A. tritici cannot survive in soil for more than 1 year if the soil is left fallow or planted to a non-host crop. The pest will be eliminated in more than a year.
Hot-water treatments may be used to eradicate A. tritici from seed lots (Suryanarayana and Mukhopadhaya, 1971). Marcinowski (1909) demonstrated that nematode galls in a seed lot could be destroyed by keeping the mixture in water at 54-56°C for 10-12 minutes. Pre-soaking the seeds before the hot-water treatment has also been advocated (Byars, 1919; Chu, 1945).
Another hot-water treatment involves pre-soaking the seed at 21-27°C for 2-4 hours, then placing them in water for 30 minutes at 50°C. The seeds are rinsed in tap water, then spread in thin layers on a clean surface till dry (Byars, 1920; Leukel, 1924).
Jones et al. (1938) developed an indented cylinder machine which separated oval wheat seeds from globular nematode galls; the device was claimed to be 98% effective in removing the seed galls. Chu (1945) also designed a machine to separate nematode galls from healthy grain.
Nematicidal plants are not as effective as the clean seed or fallow method and offer little hope as an effective method of controlling A. tritici.
There are few reports concerning biological control of A. tritici.
A large number of plants have been evaluated for resistance to A. tritici over a period of more than 60 years. A few resistant plants have been found, such as the wheat cultivar Kanred (Leukel, 1924); however, resistance does not appear to be a viable solution to the problem of seed gall nematodes.
Many chemicals have been used to control A. tritici; they were not highly effective and most are no longer available. Early investigations of the disinfection of contaminated seed produced varying results. Marcinowski (1909), Byars (1919), and Sommerville (1919) reported that contaminated seed could not be thoroughly disinfected without injuring the wheat seed. Chu (1945) obtained good results with corrosive sublimate.
ReferencesTop of page
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ContributorsTop of page
06/07/18 Updated by:
Andrea M Skantar, Mycology and Nematology Genetic Diversity and Biology Laboratory, USDA-ARS, Beltsville, Maryland, USA
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