Root-lesion nematode

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Scientific name: Pratylenchus spp.

Other name: Nematic root rot

Taxonomy

 

Class

Secernentea

Order

Tylenchida

Superfamily

Tylenchoidea

Family

Pratylenchidae

Genus

Pratylenchus

 

Geographical distribution

 

Asia, the Pacific, America, and other tropical and temperate areas where sweetpotato is grown.

 

Economic importance

Pratylenchus is considered second only to Meloidogyne in terms of plant species parasitised and extent of crop damage and loss. The thresholds vary somewhat with species, climate, soil type and host crop but a density of 1-2 nematodes g-1  soil at planting is a reasonable guide; thresholds range from 0.5-1.8 g-1  soil.

In Japan the principal species is P. coffeae,  which caused significant losses, while in the U.S., P. brachyurus, is the most common.

Symptoms

The nematode causes small, necrotic root lesions. Fibrous root necrosis may lead to some stunting of vines and a significant reduction in the quality of fleshy storage roots. Small, brown to black, necrotic lesions are also produced on storage roots, which make the roots unmarketable.

Morphology

Lesion nematodes are small nematodes with adults, being usually less than 1 mm long. The head region is low and flattened, with 2- 4 head annules.  It has distinct head skeleton, continuous with the  body contour. The stylet is 20 Ám or less, and moderately developed with distinct basal knobs. The esophagus has a well developed median bulb, and the posterior gland lobes overlap the intestine ventrally. The female has posterior vulva (V= 70-80%) with a single anterior gonad and a short post vulval sac; It is tall, cylindrical to conoid, and with two to three anal body widths long (?).  The male tail is conical with a distinct bursa that reaches the tail tip.

Life cycle

This genus has the typical nematode life cycle with four juvenile stages, and the adults in some species are parthenogenic and in others amphimictic. The juveniles of P. coffeae mature and differentiate within the root, and adult females deposit eggs singly or in small groups within the tissues of the root. Commonly, the duration of the Pratylenchus life cycle is given as about 35-42 days, but this, considerably varies with species, e.g. P. penetrans can range from 30-86 days (Corbett, 1973) while P. coffeae in sweetpotato is from 30-40 days at 25-30oC to 50-60 days at 20oC. The variability is due partly to the length of the life cycle being temperature dependent (Corbett, 1973; Townshend and Anderson, 1976).

Ecology

Lesion nematodes are migratory root endoparasites. They are also extremely diverse in their adaptive capacity. Individual species show special preferences for temperature. Some are less able than others to tolerate extremes, especially cold, or the extreme drought areas, where vegetable production is less common except under irrigation. The influence of moisture as rain is not as significant. However, P. penetrans moves best when soil water has drained so that 8-12% of the soil volume is air-filled  and survives a shorter time in wet than in dry soil . Preferred soil types include coarse-textured sandy loam, silt loam or occasionally, organic soil (muck). More P. penetrans penetrate roots in a sandy loam than in silt loam or loam. They are less common in clays and similar fine-textured soils; adults and juveniles of P. penetrans move farther in coarse than in fine-textured soil. Pratylenchus may be disseminated by transportation of plant root parts or soil, and by surface or irrigation water.

Management

Cultural control

Crop rotation. Peanut crops resulted in significantly lower population of P. coffeae. Paddy rice or increase fertilization with potassium reduced severity of infection.

Addition of organic amendments. Chicken manure is very effective in reducing the nematode.

Biological control

Paecilomyces lilacinus, a fungal egg parasite was evaluated and found effective against Pratylenchus sp. in corn.

Chemical control

Use of soil fumigants.

References

Clark, C.A. and J. Moyer. 1988. Compendium of Sweet Potato Diseases. APS Press. 74 p.

Corbett, D.C.M. 1973. Pratylenchus penetrans. CIH Descriptions of plant parasitic nematodes. Set 2, No. 25. Commonwealth Institute of Helminthology, St. Albans, UK.

Evans, K, D. L. Trudgill and J. M. Webster. 1993. Plant Parasitic Nematodes in Temperate Agriculture. University Press, Cambridge. 648 p.

Filipjev, I.N. and  Schuurmans Stekhoven, J.H. 1941. A manual of agricultural helminthology.  Leiden : Brill. 878 p.

Gapasin R..M. 1996. Evaluation of Paecilomyces lilacinus (Thom.) Samson for the control of Pratylenchus sp. in corn. Biocontrol 1: 41-49.

Goodey, T. 1933. Plant parasite nematodes and the diseases they cause. London. 306 p.

Yoshida, T. 1985.Correlation between successive yield tests for agronomic characters in sweetpotato. Jpn. J. Breed. 35: 204-208.

Contributed by: Ruben Gapasin

Taxonomy

Economic importance

Geographical distribution

Symptoms

Morphology

Life cycle

Ecology

Management

References


Sunken lesions induced by root-lesion nematode (H. Kawagoe & H. Nakasono, APS).