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2003 Plant Management Network.
Accepted for publication 4 April 2003. Published 13 May 2003.


Diagnosis of Peltamigratus christiei, a Plant-Parasitic Nematode Associated with Warm-Season Turgrasses in the Southern United States


W. T. Crow, Entomology and Nematology Department, University of Florida, Gainesville 32611; and N. R. Walker, Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater 74078


Corresponding author: W. T. Crow. wtcr@ifas.ufl.edu


Florida Agricultural Experiment Station Journal Series No. R-09182.


Crow, W. T., and Walker, N. R. 2003. Diagnosis of Peltamigratus christiei, a plant-parasitic nematode associated with warm-season turfgrasses in the southern United States. Online. Plant Health Progress doi:10.1094/PHP-2003-0513-01-DG.


Introduction

Various turfgrass species are used as ground cover for residential, commercial, right-of-way, and recreational purposes in the southern United States. Increases in population density and urbanization in the South have led to an increase in both warm-season turfgrass use and its importance as a horticultural commodity. In many southern states, turfgrass and related industries are significant contributors to local and regional economies. The increasing importance of turfgrass has led to greater emphasis on diagnosis and management of turfgrass pests, including plant-parasitic nematodes. Turfgrass samples comprise more than 90% of the diagnostic samples evaluated in the University of Florida Nematode Assay Laboratory.

Plant-parasitic nematodes are common and destructive pests of both warm- and cool-season turfgrasses. The most common warm-season grasses in the southern United States include bermudagrass (Cynodon dactylon), St. Augustinegrass (Stenotaphrum secundatum), bahiagrass (Paspalum notatum), centipedegrass (Eremochloa ophiuroides), and zoysiagrass (Zoysia spp.). These grasses are often found growing on sandy soils favoring damaging populations of plant-parasitic nematodes. The population diversity and distribution of plant-parasitic nematodes in numerous turfgrass ecosystems have been characterized (5,8,13,15,16). In these studies, nematodes from the genera Belonolaimus, Mesocriconema, Helicotylenchus, Hemicycliophora, Hoplolaimus, Paratrichodorus, Pratylenchus, Meloidogyne, Trichodorus, and Tylenchorhynchus were associated with both warm- and cool-season grasses. Belonolaimus longicaudatus and Hoplolaimus spp. are among the most destructive turfgrass nematodes. In addition, Meloidogyne spp. can be destructive to various warm-season turfgrasses, such as bermudagrass, when grown on sandy soils.

Peltamigratus christiei (Fig. 1A and 1B) has been reported from Florida turfgrass ecosystems for many years (4) and is the only species of Peltamigratus reported parasitizing warm-season turfgrasses. Originally thought to be confined to tropical climates, the authors have recently identified P. christiei associated with bermudagrass in California, Mississippi, and Oklahoma. On some crops, Peltamigratus spp. can be easily mistaken for nematodes in the genera Scutellonema or Aorolaimus. However, on turf P. christiei is most often confused with the common turf parasites Hoplolaimus spp. and Helicotylenchus spp.


 
A


B
 
  Fig. 1. Female (A) and male (B) of Peltamigratus christiei.  

When viewed under low magnification, P. christiei may be confused with other plant-parasitic nematodes, including Hoplolaimus spp. and Helicotylenchus spp. Correct diagnosis of this nematode is important, as its virulence is most likely different from nematodes in these other genera. Depending on the type of nematode for which it is mistaken, misidentification could result in an unnecessary nematicide application or lack of a nematicide application where it would be beneficial. The objective of this report is to describe P. christiei and the characteristics which can be used to readily distinguish it from Hoplolaimus spp. and Helicotylenchus spp. when examining nematode populations from warm-season turfgrasses. This article emphasizes features that can be observed with a dissecting, or low-magnification inverted microscope rather than those requiring the use of high resolution microscopy.


Hosts

Bermudagrass (Cynodon dactylon), St. Augustinegrass (Stenotaphrum secundatum), bahiagrass (Paspalum notatum).


Pathogen

Peltamigratus christiei (Golden and Taylor, 1956) Sher, 1964 (Nematoda: Hoplolaimidae);

syn. Rotylenchus christiei (Golden and Taylor, 1956),

Scutellonema christiei (Golden and Taylor) Andrassey, 1958,

Aorolaimus christiei (Golden and Taylor) Fortuner, 1987.


Taxonomy

Peltamigratus christiei was first described by Golden and Taylor (4) as Rotylenchus christiei. Sher (10) later placed R. christiei in a new genus Peltamigratus. Fortuner (2) synonymized the genus Peltamigratus with Aorolaimus. However, Siddiqi (12) resurrected the genus Peltamigratus. In this paper, we retain the genus name Peltamigratus as in Siddiqi (12).


Symptoms

No symptoms specific to P. christiei on turfgrasses have been described, but are probably typical to those caused by other ectoparasitic nematodes on turfgrasses. These include irregular patches of declining turf that exhibit wilting, chlorosis, thinning, or death (14). These symptoms have been observed in areas with high populations of P. christiei in the field (Fig. 2). Affected roots may appear abbreviated, darkened, or exhibit rotting.


 

Fig. 2. Irregular patches of declining turf in a St. Augustinegrass lawn associated with high (> 300/100 cm3 of soil) population densities of Peltamigratus christiei.

 

Host Range

Cerothamnus sp. (wax myrtle), Crinum americanum (swamp lily), Cynodon dactylon (bermudagrass), Hibiscus cannabinus (Indian hemp), Paspalum notatum (bahiagrass), Paspalum vaginatum (seashore paspalumgrass), Quercus sp. (oak), Sabal spp., Stenotaphrum secundatum (St. Augustinegrass), Theobroma cacao (cacoa).


Geographic Distribution

California, Florida, Mississippi, and Oklahoma in the United States. Peltamigratus christiei has also been reported in Brazil (3).


Pathogen Isolation

Peltamigratus christiei is primarily an ectoparasite of roots. Therefore, any of the common methods of extracting nematodes from soil (7) should be adequate for isolating P. christiei. The most common methods used by nematode diagnostic services are variations of sugar-flotation with centrifugation or Baermann funnel methods.


Pathogen Identification

On turf, P. christiei is most commonly mistaken for nematodes in the genera Hoplolaimus and Helicotylenchus, which are widespread turfgrass parasites (Fig. 3). The most easily identifiable morphological features that distinguish P. christiei from nematodes in these genera are body size, body position when dead, vulval position, tail shape, and the presence of epiptygmata.


 

Fig. 3. Peltamigratus christiei (a), Hoplolaimus galeatus (b), and Helicotylenchus pseudorobustus (c).

 

The female body length of P. christiei is 0.67 to 0.87 mm (10). The female body length of Hoplolaimus galeatus, the most common species of lance nematode associated with turf, is 1.24 to 1.94 mm (9). The female body lengths of the two most commonly encountered Helicotylenchus spp. associated with turf in Florida, H. pseudorobustus and H. dihystera, are 0.60 to 0.82 mm, and 0.59 to 0.79 mm, respectively (11). Therefore, P. christiei is shorter than Hoplolaimus spp., but its range overlaps that of Helicotylenchus spp. (Fig. 3).

The vulval position of P. christiei is 53 to 58% of the body length from the anterior (4,10). The vulval position of H. galeatus is 52 to 60% from the anterior (9). Helicotylenchus pseudorobustus and H. dihystera have vulval positions of 59 to 64%, and 60 to 65%, respectively (11). Therefore, the vulval position of P. christiei is anterior to that of the Helicotylenchus spp. commonly found on turf, but not different from that of H. galeatus.

Death position can be very useful for distinguishing P. christiei from common Hoplolaimus spp. and Helicotylenchus spp. on turf. In death, the body position of P. christiei is usually a loose spiral or C shape (Fig. 4A). The head seldom overlaps the tail to form a complete spiral. In contrast, the death position of H. pseudorobustus and H. dihystera is usually a tight spiral, with the head generally overlapping the tail (Fig. 4B). The death position of Hoplolaimus spp. is more or less straight or slightly curved (Fig. 4C).


     
 

Fig. 4A. In death the body of female Peltamigratus christiei (a) is curved, but usually does not form a full spiral. Males (b) are often not curved when dead.

 

Fig. 4B. In death the bodies of the Helicotylenchus spp. common on turf usually form a full spiral with the head overlapping the tail at least once.

 

 

Fig. 4C. In death the body of Hoplolaimus spp. is usually straight or slightly curved.

 

Tail shape is also useful in distinguishing P. christiei from Hoplolaimus spp. and Helicotylenchus spp. on turf. The female tail of P. christiei is rounded and may be slightly asymmetrical (Fig. 5A). The female tail of H. galeatus is short and symmetrical (Fig. 5B). The female tails of H. pseudorobustus and H. dihystera are distinctly asymmetrical, being curved ventrally and often having a short terminal projection (Fig. 5C).


     
 

Fig. 5A. The female tail of Peltamigratus christiei is slightly asymmetrical and curved ventrally.

 

Fig. 5B. The female tail of Hoplolaimus spp. is symmetrical and bluntly rounded.

 

 

Fig. 5C. The female tail of the Helicotylenchus spp. common on turf is asymmetrical and curved ventrally, and often a terminal projection is present.

 

The most useful diagnostic tool for separating P. christiei from Hoplolaimus spp. and Helicotylenchus spp. on turf is the presence of epiptygmata. Epiptygmata are sclerotized projections surrounding the vulva of certain species of nematodes (Fig. 6). Peltamigratus christiei has two prominent epiptygmata that are easily observed with most microscopes (Fig. 7A). Some other species of Peltamigratus have only a single epiptygma. Epiptygmata are not present in Hoplolaimus spp. (Fig. 7B) or Helicotylenchus spp. (Fig. 7C).


 

Fig. 6. Scanning electron micrograph of epiptygmata, sclerotized vulval projections, on a female Peltamigratus christiei. Peltamigratus christiei has two epiptygmata, some other species of Peltamigratus have only a single epiptygma (Photo courtesy of K. B. Nguyen).

 

 

Fig. 7A. Epiptygmata are easily seen surrounding the vulva of Peltamigratus christiei.

 

Fig. 7B. The vulva of Hoplolaimus spp. lacks epiptygmata.


 

Fig. 7C. The vulva of Helicotylenchus spp. lacks epiptygmata.

 

The intent of this paper is to help identify P. christiei from common nematodes found in turfgrass samples in the southern United States. On occasion, other nematodes also may be confused with P. christiei. Scutellonema spp. and Aorolaimus spp. very much resemble P. christiei, and females may be indistinguishable using low resolution microscopy. While there are no published reports of Scutellonema spp. parasitizing warm-season turfgrasses, they are occasionally found in turf samples submitted to the University of Florida Nematode Assay Laboratory. Since males are abundant in populations of P. christiei, the shape of the bursa (caudal alae) is a useful feature to separate it from species of Scutellonema. The bursa of P. christiei extends beyond the tail tip when seen in lateral view (Fig. 8A). In many Scutellonema spp. males are rare. When Scutellonema males are present, the bursa does not extend beyond the tail tip when seen in lateral view (Fig. 8B). If observation at high magnification using oil immersion is possible, scutella (large phasmid) location is the primary feature used to separate the genera Peltamigratus, Scutellonema, and Aorolaimus. The scutella of Scutellonema are located near the anus and are nearly opposite each other on the nematode body. In Peltamigratus and Aorolaimus the scutella are anterior to the anus and not opposite each other. Aorolaimus has one scutella anterior and the other posterior to the vulva. Peltamigratus has both scutella posterior to the vulva. See Sher (9,10,11) for a detailed description of each genus.


     
 

Fig. 8A. The bursa of P. christiei extends beyond the tail tip in lateral view.

 

Fig. 8B. The bursa of Scutellonema spp. does not extend beyond tail tip in lateral view.

 

A general key to genera of plant-parasitic can be very helpful in diagnosing plant-parasitic nematodes. Mai et al. (6) has both pictorial and non-pictorial keys and is an excellent resource for nematode diagnostic laboratories. Keys specific to the Hoplolaiminae, the suborder containing all the genera dealt with in this paper (Aorolaimus, Helicotylenchus, Hoplolaimus, Peltamigratus, and Scutellonema), are found in Siddiqi (12). The most current key to species in the genera Peltamigratus and Aorolaimus is Baujard et al. (1).


Literature Cited

1. Baujard, P., Castillo, P., Doucet, M., Martiny, B., and Mountport, D. 1994. Taxonomic studies on the genus Aorolaimus Sher, 1963 (Nemata: Hoplolaimidae). 1. Bibliographic analysis and tentative key to species. Fundam. Appl. Nematol. 17:103-115.

2. Fortuner, R. 1987. A reappraisal of Tylenchina (Nemata). 8. The Family Hoplolaimidae Filip'ev, 1934. Rev. Nematol. 10:219-232.

3. Friere F. C. O., and Montiero, A. R. 1978. Nematodes of Amazonia. II. Parasitic and free-living nematodes associated with black pepper (Piper nigrum L.) and cocoa (Theobroma cacao). Acta Amazonica 8:561-564.

4. Golden, M. A., and Taylor, A. L. 1956. Rotylenchus christiei, n. sp., a new spiral nematode species associated with roots of turf. Proc. Helminthol. Soc. Wash. 23:109-112.

5. Lucas, L. T., Blake, C. T., and Barker, K. R. 1974. Nematodes associated with bentgrass and bermudagrass golf greens in North Carolina. Plant Dis. Rep. 58:822-824.

6. Mai, W. F., and Mullin, P. G. 1996. Plant-Parasitic Nematodes: A Pictorial Key to Genera. Cornell University Press. Ithaca, NY.

7. McSorley, R. 1987. Extraction of nematodes and sampling methods. Pages 13-47 in: R. H. Brown and B. R. Kerry, eds. Principles and Practice of Nematode Control in Crops. Academic Press Australia, Marrickville, Australia.

8. Murdoch, C. L., Tashiro, H., and Harrison, M. B. 1978. Plant-parasitic nematodes associated with golf putting-green turf in New York. Plant Dis. Rep. 62:85-87.

9. Sher, S. A. 1963. Revision of the Hoplolaiminae (Nematoda). II. Hoplolaimus Daday, 1905 and Aorolaimus n. gen. Nematologica 9:267-295 9:455-467.

10. Sher, S. A. 1963. Revision of the Hoplolaiminae (Nematoda). IV. Peltamigratus n. gen. Nematologica 9:455-467 9:267-295.

11. Sher, S. A. 1966. Revision of the Hoplolaiminae (Nematoda). II. Helicotylenchus (Steiner, 1945). Nematologica 12:1-56.

12. Siddiqi, M. R. 2000. Tylenchida: Parasites of plants and insects. CABI Publishing, New York, NY.

13. Sikora, E. J., Geurtal, E. A., and Bowen, K. L. 2001. Plant-parasitic nematodes associated with hybrid bermudagrass and creeping bentgrass putting greens in Alabama. Nematropica 31(2):301-305.

14. Smiley, R. W., Dernoeden, P. H., and Clarke, B. B. 1992. Compendium of Turfgrass Diseases. 2nd ed., The American Phytopathological Society, St. Paul, MN.

15. Todd, T. C., and Tisserat, N. A. 1990. Occurrence, spatial distribution, and pathogenicity of some phytoparasitic nematodes on creeping bentgrass putting greens in Kansas. Plant Dis. 74:660-663.

16. Walker, N. R., Goad, C., Zhang, H., and Martin, D. L. 2002. Factors associated with populations of plant parasitic nematodes in bentgrass putting greens. Plant Dis. 86:764-768.