Plant­Parasitic Nematodes

Gary W. Lawrence

One of the most serious pests associated with kenaf production in Mississippi and practically every country where the crop has been produced is the plant­parasitic nematode. Plant­parasitic nematodes are multicellular, microscopic worm­like animals that feed primarily on the root systems of plants. These animals use a specialized mouth part (a stylet) to puncture the cells of the root and withdraw the cellular contents.

Typically, plant­parasitic nematodes feed either from the outside of the root as an ectoparasite or inside the root tissue as an endoparasite. The ectoparasitic nematodes will damage the plant by feeding on the epidermal root cells. The endoparasitic nematodes will enter the root and establish a permanent residency by altering the plants physiology. The nematode will induce the plant to produce specialized nurse cells inside enlarged roots or root galls. The nurse cells act as a sink to divert the natural flow of nutrients produced by the plant to the feeding site of the nematode. The reduction in available nutrients for plant growth and development generally results in plants that may appear stunted, have yellow leaves, and have root systems which are galled, inefficient, and reduced in size.

Kenaf is parasitized by a number of species of plant­parasitic nematodes. Early research conducted in Florida identified nine species of nematodes associated with kenaf production. In Mississippi, 13 species of plant­parasitic nematodes are commonly found in the state's soils (Table 1). Sixspecies may have the potential to reduce the growth and development of kenaf.

The root­knot nematodes are the most frequently associated species on kenaf. The southern root­knot nematode is the predominant root­knot species in Mississippi and the southern United States. The nematode is also pathogenic on soybeans and is the primary root­knot species affecting cotton. The nematode has the potential to become a serious problem to kenaf production in Mississippi since both soybean and cotton are widely grown.

The major research emphasis at Mississippi State University has been directed at the southern root­knot nematode. Preliminary research has shown that this nematode will significantly reduce kenaf growth and yield. When nematodenumbers are high, plant death may result. In populations studies, it was determined that an at­plant population density of100 nematodes/cm3 soil would reduce kenaf yield by 32%. If nematode numbers are as high as 500/cm3 soil, a producer could expect reductions in yield as high as 67%. Therefore, it is recommended that a nematode analysis be conducted on all fields scheduled for use in kenaf production. If the root­knot nematode is present, options for nematode management include resistant varieties, crop rotation and the use of chemical nematicides.

We initiated a study to screen the available kenaf varieties for resistance to the root­knot nematode. Although we have not identified any varieties with resistance, the varieties do vary in the total number of nematodes that are produced. Nematode reproduction has consistently been lower on kenaf varieties

Tainung 1 and Tainung 2. A lower nematode population at harvest will result in fewer nematodes the following year.

If kenaf must be grown in a field with a previous history of root­knot infestation, reductions in total yield should be expected. To reduce nematode populations at planting, chemical nematicides have been shown to reduce nematode populations and improve kenaf yields. Currently the only nematicide that is labeled for use on kenaf is Telone II*.

The use of crop rotations are effective means of managing root­knot nematode populations. Tests are currently in progress to determine the most economical rotation crop to reduce nematode populations. Both soybeans and cotton are susceptible to the root­knot nematode; therefore, care must be taken when a variety is selected to be included in the rotation.

Although plant­parasitic nematodes have the potential to reduce kenaf growth and yields, kenaf can be successfully cultivated as an alternative crop in Mississippi. This can be accomplished by developing a plan to manage the nematode populations. A knowledge of the nematode species and populationnumbers prior to planting will allow the kenaf producer to selecta management tactic or a combination of tactics that will suit the particular needs at each location. This will ensure the production of a crop that will be profitable to the producer.

Table 1.  Nematodes common to the Mississippi Delta.            

Common Name                    Scientific Name                 



*Southern root­knot            Meloidogyne incognita (Races 1­4)

*Javanese root­knot            Meloidogyne javanica

*Peanut root­knot              Meloidogyne arenaria

 Stubby root                    Trichodorus sp.

*Stunt                          Tylenchorhynchus sp.

 Stunt                          Quinisulcius sp.

 Ring                           Criconema sp.

 Spiral                         Helicotylenchus sp.

 Lesion                         Pratylenchus sp.

 Dagger                         Xiphinema sp.

*Reniform                       Rotylenchulus reniformis

*Lance                          Hoplolaimus magnistylus

 Soybean cyst                   Heterodera glycines

 Yam                           Scutellonema sp.                 

*Nematode species considered to be a potential threat to kenaf.

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Gary W. Lawrence is an Assistant Professor, Nematology Department of Entomology and Plant Pathology, Mississippi State University.