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Stem and Bulb Nematode, an Important Pest of Vegetables and Other Crops | AG1304 |
Motiul Quader and Lila Nambiar, Knoxfield
October 2007
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Common Name: Stem and bulb nematode
Scientific Name: Ditylenchus dipsaci (Kuhn, 1857)
Physical Description
Body shape cylindrical, transparent and straight or slightly curved when dead. Adult about 1.2 mm long ("giant race" in faba beans about 2 mm long). Lip region low, flattened anteriorly. Head skeleton moderately developed, stylet about 10-12 µm long with distinct basal knob. Median esophageal bulb with refractive thickenings; the vulva is about two thirds along the body and oocytes are usually in a single row. Post-vulval sac extending about half-way to the anus. Lateral fields with four incisures; tail terminus sharply pointed. Male and female tails conical, usually 4-7 anal body widths long; tail terminus narrowly rounded to pointed. Male bursa ends just before the tail tip; spicules rather weak.
Hosts
Wide host range, over 450 hosts, but 8-10 host races or biotypes, some with limited host range. | Figure1. Microscopic image (200x) of stem and bulb nematodes |
The common hosts are: Onions, Garlic, Daffodils, Faba beans, Oats, Leeks, Narcissus, Lucerne, Maize, Peas, Potatoes, Rye, Strawberries, Sugar beet, Tobacco, Tulips, Carnations, Celery, Lentils, Rape, Parsley, Sunflowers, Wheat (Herbarium reference collection, DPI Victoria).
There are many races but the most common races are:
| a) | Oat race: Cereals, most grains, rye, corn and oats. |
| b) | Alfalfa race: Mainly specific on certain legumes, but can infest alfalfa, many weeds and clovers. |
| c) | Bulb race: Most bulbs, daffodil and tulip. |
Some of the races can interbreed and their progeny have different host preferences.
Nematode Invasion Symptom on Hosts
| a) | Common symptoms: Restricted growth of plants. In severe cases yellowish, swelling and distorted leaves/bulbs. |
| b) | In onions, garlic: Bloated, twisted, swollen leaves, distorted and cracked bulbs with dark rings. |
| c) | In maize, oats and rye: Extra tillers, swollen leaf bases. |
| d) | In clover and alfalfa: Reduction of inter-node length and swollen stems. |
Pathogenicity
Infested tissues become spongy, distorted and predispose plants to other problems. Infestation in garlic and onion can be epidemic. Infestation can be spread by infected bulbs. Clovers are infected through the centre where leaf primordia, therefore, treatment can be difficult without affecting germination. In some plant species, nematode move to inflorescence and can stay in seeds for long periods. In such case seeds are major source of nematode dispersal e.g. beans, clover, alfalfa. The infestation in alfalfa occurs readily in heavier soils and during high rainfall or in sprinkler-irrigated areas. Affected fields show irregular plant growth. Nematodes can spread around field by equipment or irrigation water. D. depsaci predisposes plants to other disease e.g. Alfalfa to fungus Hytophthora megasperma.
Economic Importance
D. dipsaci is a devastating plant parasitic nematode, especially in temperate regions. It can cause serious problems on onions, garlic, cereals, legumes, strawberries and ornamental plants.
Geographical Distribution
Cosmopolitan, especially in temperate regions
Life Cycle | Figure 2. Stem & bulb nematode infested garlic
Figure 3. Geographical distribution of stem and bulb nematodes (After European and Mediterranean Plant Protection Organisation, EPPO
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D. dipsaci is a migratory endoparasite, which reproduce sexually within 19-23 days at 15 OC. Nematodes can live 45-75 days when sexually mature. A female can produce 200-500 eggs. The first molt stage occurs inside the egg; 2nd and 3rd molt in soil and /or outside tissues or between surfaces of plant tissues. The nematodes can survive in soil for as long as two years without principal host, probably feeding on fungi. Fourth stage juveniles enter into young tissues, especially in seedlings when below the soil surface. Migration to above ground plant parts usually occurs with the rain water or sprinkler irrigation and enters into tissues through stomata or by direct penetration. Fourth stage is the survival stage, which can go cryptobiosis (hidden life) on or below surface of plant tissue and survive 3-5 years (up to 23 years in museum specimens).
Management | Figure 4. Life cycle of stem and bulb nematode. After G.N. Agrios, Plant Pathology, Academic Press Inc.) |
A. Control
- Hot-water treatments with different temperature and time combinations are operational and efficient in control. However, this method is dependent on type and state of seed material.
- Systemic nematicides may be effective to some extent.
- Soil fumigation (usually not economical).
- Hand lifting and destroying the affected plants (bulbs) together with a margin of surrounding healthy area of field followed by chemical treatment may sometimes be effective in treating small patches.
- It is also important to eradicate and destroy a small infestation before it spreads.
- The use of tolerant or resistant cultivars can also reduce the damage.
B. Phytosanitary measures
At present, the distribution of D. dipsaci in Australia is limited to areas of Victoria, South Australia and Western Australia. It is certain that D. dipsaci may cause complete failure of host crops without any control measure. The European and Mediterranean Plant Protection Organisation (EPPO) list it as a pest of quarantine significance. The implementation of certification schemes for the production of host plants of D. dipsaci can provide planting material free from the pest. Imports of soil and plants for planting and seeds of host plants from areas/countries where this nematode occurs should be restricted. The following sample size and procedures are recommended for the Phytosanitary measurement.
Plant and soil sampling
Sample sizes
- Visually inspect entire lot of plants prior to sampling.
- Determine sample size based on lot size. A minimum of 5 plants or 5% of the first 200 plants, and an additional 2% of lot size over 200 plants.
Sampling procedures
- Composite samples within a plant species by variety, and/or container size.
- Select plants at random. Do not limit sample to only plants that look “unhealthy”.
- Collect soil and root samples from small pots by carefully inverting and un-potting plants.
- Collect roots and adhering soil mainly from the inner mass of root growth. Avoid collecting only peripheral roots on soil surface and inner perimeter of the container.
- Sample should consist of any root primordia or root nubbins, any aerial roots, or the basal section cut from the cane to include at least one node.
Seed sampling procedure
1. Seed lot and sample sizes
There are a number of recommendations for lot size for seed health test. However, according to ISTA (International Seed Testing Association) the maximum lot sizes would be up to 10 tonnes for small-seeded crops and up to 40 tonnes for large-seeded crops. Examples of seed lot size and seed sample size of various crops have been presented in Table 1.
2. Sampling procedures
It is important to collect a representative sample of a seed lot in order to obtain accurate diagnostic test result. The followings are the guideline to collect a representative sample from bulk or bags:
- Take several sub samples from different horizontal and vertical positions in the lot at random. The weight of sub samples should about four times the weight of the final required sample size. Combine the sub samples and mix thoroughly.
- Spread the combined and well mixed sub samples on a smooth, clean surface and prepare a long mound of seed. Divide the seed mound into two equal portions longitudinally. Continue to halve each portion to obtain two parallel rows of four samples per row.
- Collect first and third sample in one row and the second and fourth sample in the other row and discard the remaining four samples. Combine the four remaining samples.
- Repeat steps 2 and 3 until the required sample weight for submission is obtained.
Table 1. Example of seed lot and sample sizes for nematode testing, including stem and bulb nematode.
Crops | Seed lot size (Kg) | Sample size (g) |
Garlic | 10,000 | 25 |
Oat | 25,000 | 1,000 |
Faba Bean | 25,000 | 1,000 |
Lucerne | 10,000 | 250 |
Basil | 10,000 | 40 |
Beet | 20,000 | 500 |
Celery | 10,000 | 25 |
Cabbage | 10,000 | 200 |
Lentil | 10,000 | 1,000 |
Lettuce | 10,000 | 50 |
Maize | 40,000 | 1,000 |
NB: Seed sample sizes that are not in this list can be estimated based on closest seed size above
C. Sample testing facility in Department of Primary Industries, Victoria:
- By post: Nematology, Private Bag 15, Ferntree Gully DC, VIC 3156.
- By person: Nematology, 621 Burwood HWY, Knoxfield, VIC 3180.
More Information
- Search using scientific name and vernacular names in all the web e.g. Google (external site); Yahoo (external site)
- Search using specialised databases: GenBank; CABI; Current Content
- This Agriculture Note can be accessed through the DPI web site
- General inquiries: contact the DPI Call Centre on 136 186
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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