Meloidogyne incognita

Taxonomy, Common Name, Disease

Hosts

Very broad host range. More than 700 hosts. These include most cultivated crops and ornamentals.

Distribution

Worldwide but more common in temperate, subtropical and tropical areas. The cosmopolitan distribution of some species is the result of the movement of rooted plants in commerce and at the local level through movement of water, soil and equipment and rooted seedlings of crop plants and ornamentals.

Life Cycle

Sedentary endoparasite, parthenogenic. Second-stage infective juveniles hatch from the eggs. These invade roots in the region of elongation near the root cap. They migrate between and through cells and position themselves with the head in the vascular tissues. Cell damage occurs as a result of the migration and if several juveniles enter the root tip cell division stops and there is no root elongation. As feeding continues several cells near the head begin to enlarge and become multinucleate. These are called giant cells and there are usually 3 to 6 associated with each nematode. The formation of giant cells and galls is the result of cell enlargement and of increased numbers of cells. These changes are induced by substances (salivary secretions) introduced into cells and surrounding tissues during the feeding of the nematode. During this process the xylem vessels become disrupted and the roots cannot function normally with respect to water and nutrients. During the process of gall formation the nematodes undergo the second, third and fourth molts to reach the adult stages. Mature females are saccate (pear-shaped) and lay eggs into a gelatinous matrix. This matrix may protrude from the surface of small roots or may be entirely within the gall. Eggs hatch in about 7 days. The entire life cycle is completed in 20-25 days at 70F. Males are vermiform. Males are not required in reproduction.

Symptoms-Pathogenicity

Reduced root systems and galling. There is poor top growth and the foliage is frequently chlorotic (yellow) because essential elements are not taken in and transported by the impaired root system. Severe infections cause wilting of the foliage and the plants require more frequent irrigations.

Management

Preplant nematicides. Postplant nematicides on some perennials. Some resistant or immune varieties and rootstocks are available in tomato, bean, sweet potato, peach, almond, walnut and grape. Hot water treatment of rooted grape cuttings 125F for 5 minutes will give 100 percent control. Because of broad host range, crop rotation is frequently not feasible.

Characteristics

Sexually dimorphic. Female saccate to globose, 0.4-1.3 mm long, usually embedded in root tissue which is often swollen or galled; body soft, pearl-white in color and does not form a cyst; the neck protrudes anteriorly and the excretory pore is anterior to the median bulb often near the stylet base; the vulva and anus are terminal, flush with or slightly raised from the body contour; the cuticle of the terminal region forms a characteristic pattern, the perineal pattern, which is made up of the stunted tail terminus, phasmids, lateral lines, vulva and anus surrounded by cuticular striae; the pattern is often characteristic for individual species. The female stylet is shorter, 10-24 um usually 14-15 um, and more delicate than in Heterodera with small basal knobs which are of a characteristic shape for some species. The paired gonads have extensive convuluted ovaries that fill most of the swollen body cavity. There are six large unicellular rectal glands in the posterior body which produce a gelatinous matrix which is excreted via the rectum to form an egg sac in which the many eggs are deposited. Males vermiform, similar to Heterodera, but the lip region has a distinct head cap which includes a labial disc surrounded by lateral and medial lips. The head skeleton is usually weaker than Heterodera and the stylet less robust and shorter, 18-24 um long for many species. Infective second stage juveniles, often free in the soil, are usually 0.3-9.5 mm long; they are less robust than Heterodera juveniles, the stylet is delicate with small basal knobs, under 20 um long, and the head skeleton weak. The median esophageal bulb is well developed and the esophageal glands are extensive, overlapping the intestine for several body widths mainly ventrally; the tail is conoid often ending in a narrow rounded terminus but tail length variable, 1.5-7 anal body widths, between species, it often ends in a clear hyaline region the extent of which can help to distinguish species.

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. Orton Williams, K.J.1973. Meloidogyne incognita. C.I.H. Descriptions of Plant-parasitic Nematodes. Set 2, No. 18. Commonwealth Institute of Parasitology. C.A.B. International. 4 pages.
  3. Nickle, W.R. 1984. Plant and Insect Nematodes. Ma-215).ekker, Inc. New York. 925 pages.
  4. Radewald, J.D. 1978. Nematode diseases of Food and Fiber Crops of the Southwestern United States. University of California, Division of Agricultural Sciences Priced Publication 4083. 64 pages.
  5. Nickle, W.R. 1991. Manual of Agricultural Nematology. Marcel Dekker, Inc., New York. 1035 pages.