Ditylenchus dipsaci

Taxonomy, Common Name, Disease

Historical

Genus described in 1934, but includes one of oldest known plant parasites (Anguillula dipsaci . Kuhn 1857).

Hosts

Wide host range. Over 450 hosts complicated by there being 8-10 host races or biotypes, some with limited host range. Oat race: polyphagous, most grains, rye, corn, and oats. Alfalfa race: rather specific, but alfalfa, many weeds, clovers. Bulb race: most bulbs, daffodil, narcissus, and tulip. Other hosts include onion, garlic, carrots, peas, potatoes, strawberry, sugarbeets; apples and peaches in nurseries; weeds.

Distribution

Cosmopolitan, especially in temperate regions.

Life Cycle

Sexually reproducing; life cycle is 19-23 days at 15 C. First molt within the egg. Nematodes live 45-75 days when sexually mature; females each produce 200-500 eggs. Fourth stage juvenile (J4) is survival stage; can go into cryptobiosis (literally "hidden life") on or below surface of plant tissue - eelworm wool - 3-5 years survival (up to 23 years in museum specimens). Nematode is a migratory endoparasite. At the beginning of the crop season, 4th-stage juvenile enters young tissues, especially seedlings when below the soil surface. Feeding breaks down middle lamellae; nematode probably secretes a pectinase enzyme; plant parts become "crisp" and are easily broken. Migration on plant parts above ground requires free water, and may occur after rain or sprinkler irrigation in alfalfa. Nematode enters through stomata or by direct penetration. Survives in soil without host for as long as 2 years, probably feeding on fungi.

Symptoms-Pathogenicity

Plants become distorted and stunted; infected tissues are spongy; damage can predispose plants to other problems. Alfalfa - infestation occurs readily in heavier soils and during times of high rainfall or in sprinkler-irrigated areas. Field shows irregular areas of sparse growth. Clover and alfalfa show reduction of internode length and swollen stems. Nematode is spread around field by equipment, irrigation; spreads readily in tail water. Stand reductions up to 50% following high fall populations. Predisposes alfalfa to Phytophthora megasperma. Onions, garlic - bloated, twisted, swollen leaves, distorted and cracked bulbs. On garlic, infestation can become epidemic; nematode introduced into Venezuela in Mexican varieties of garlic; up to 90% crop loss can occur. Cloves are infected through to the center where leaf primordia are located; therefore, treatment is difficult without affecting germination. Oats and rye - extra tillers, swollen leaf bases. Narcissus: leaves distorted, yellowish swelling (Dutch call it "Spikkels"), bulbs with dark rings. In some plant species, inflorescence becomes infested, and pests are spread in the seed, e.g., beans, clover, and alfalfa; infestation can also be spread by infected bulbs.

Management

For many years planting stock of daffodils and garlic was treated with a mixture of hot-water and formalin. The formalin label is no longer supported but stock on hand can be used up. Systemic insecticides (none registered in CA) are effective. In California, fenamiphos (Nemacur 3) and oxamyl are registered for use on garlic. Resistant alfalfa strains (cv. Lahontan) can be used, but this cv. is winter dormant, and is not suitable for the desert southwest. Resistant cereal varieties. Soil fumigation is usually not economical.

Importance

Causes serious problems on daffodils, garlic and alfalfa.

Characteristics

Ditylenchus - Slender nematodes, straight or slightly curved when killed by heat. Lip region low, flattened anteriorly, more or less continuous with the body contour. Head skeleton and stylet similar to Anguina. Median esophageal bulb with refractive thickenings; the vulva is about two thirds along the body and oocytes are usually in a single row. 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.

References

  1. Evans, K., D.L. Trudgill, and J.M. Webster. 1993. Chapter 1. Extraction, Identification and Control of Plant Parasitic Nematodes. in Plant Parasitic Nematodes in Temperate Agriculture. CAB International, UK. 648 pages.
  2. Hooper, D.J. 1972. Ditylenchus dipsaci. C.I.H. Descriptions of Plant-parasitic Nematodes. Set 1, No. 14. Commonwealth Institute of Parasitology. C.A.B. International. 3 pages.
  3. Agrios, G.N. 1969. Plant Pathology. Academic Press, New York. 629 pages. (page 538).
  4. Nickle, W.R. 1984. Plant and Insect Nematodes. Marcel Dekker, Inc. New York. 925 pages. (page 348).
  5. Nickle, W.R. 1991. Manual of Agricultural Nematology. Marcel Dekker, Inc., New York. 1035 pages. (page 438).