Dagger Nematode

                    Dagger Nematode (Xiphinema spp.)

             

INTODUCTION

Nematodes of the genus Xiphinema, commonly called dagger nematodes, parasitize plants. Many of these nematodes, the majority of them belonging to the Xiphinema americanum-group, can transfer viruses to plants during feeding (Taylor and Brown 1997, Gozel et al. 2006). Dagger nematodes can cause economic damage and death of host crops through feeding on the roots and also by spreading viral mosaic and wilting diseases (van Zyl et al. 2012, Jones et al. 2013). From a practical standpoint, it is a major challenge to control viral diseases in susceptible crops, partly because of a lack of resistant cultivars that should reduce populations of the virus vectors, Xiphinema spp. However, field studies have shown that some control measures, such as biofumigation and rotation of crops, targeting reduction in population of virus vectors, dagger nematodes, can be effective to some extent (Evans et al. 2007). Field surveys are required in order to implement appropriate and timely nematode management decisions that will minimize crop losses.

DISTRIBUTION AND HOSTS

Species of the genus Xiphinema are widely distributed in both temperate and tropical areas. They occur in South America, North America, Europe, Asia, Australia, New Zealand and Africa. In the U.S., Xiphinema spp. are classified as moderate pests on turfgrasses in landscapes in Massachusetts, Arkansas, California, the Carolinas (Robbins 1993, Ye et al. 2012) and Florida. Five species belonging to the Xiphinema americanum-group have been detected on tomato, grape, oak, sea grape, pines, hackberry, Brazilian pepper and citrus in Florida and Morocco (Gozel et al. 2006, Mokrini et al. 2014). Other hosts include Sudangrass (sorghum), cotton, pearl millet, turfgrasses (Wick 2012, Ye et al. 2012), legumes, sugarcane, chili pepper, banana, sugar beet, corn (Shurtleff 1980), weeds, cassava (Rosa et al. 2014) and many more.

LIFE CYCLE 

Dagger nematodes have six life cycle stages. Parthenogenesis, a form of reproduction that does not require males, is common in many, but not all species. Females lay eggs in soil. The life cycle of a dagger nematode is similar to other ectoparasitic, vermiform nematodes. Juveniles hatch from eggs and molt four times, increasing in size with each molt until they become adults. As vector-capable juveniles feed on virus-infected plants and mature into adults, they can acquire plant pathogenic viruses, commonly known as nepoviruses (nematode polyhedral viruses). The viruses form a lining in the pharynx-stylet tube and are injected into root tissues during feeding (Lamberti and Roca 1987).Dagger nematodes are ectoparasitic, which means that all stages, except eggs, attack and feed on the roots of the host plants. The nematode inserts its long stylet deep into the root while the body remains outside the root, in the soil. The stylet punctures cell walls as it penetrates plant tissues. During feeding, enzymes are secreted to digest plant cell contents. Plant parasitic nematodes produce enzymes such as cellulases, pectinases, hemi-cellulases, and chitinases, which are similar to those produced by bacteria and fungi (Jones et al. 2005, 2013), that digest and destroy root cells resulting in malformed root tissues . Root cells eventually collapse due to feeding.Species of Xiphinema are sensitive to changes in soil temperature and moisture (Malek 1969) and will migrate vertically away from desiccating conditions in topsoil; most dagger nematodes can live and survive deep in soil (Feil et al. 1997)

SYMPTOMS

The damage dagger nematodes cause to root systems is similar to that of other plant ectoparasitic nematodes. The feeding at the meristematic root-tips destroys root cells (Figure 3) and reduces root volume. Terminal galling of roots of woody plants is common (Figure 4). The above-ground effects of damaged roots are stunted growth of crops and patchy fields.Dagger nematodes transmit numerous viruses to plants. Cherry rasp leaf virus, Tomato ringspot virus, and Tobacco ringspot virus are some of the viruses transmitted by dagger nematodes during feeding. According to van Zyl et al. 2012, bermudagrass is a potential reservoir for GFLV (Grapevine fanleaf virus), which is transmitted by dagger nematodes.

MANAGEMENT

Some of the major management strategies include the following:

1. Deep plouging and solarization
2. Crop rotation: Rotation with legumes, soybean, sunflower and paddy is effective rotation with trap/antagonistic crop like sunhemp (Crololaria juncea), marigold (Tague app.), mustard (Brassica rapa), gingelly etc. can minimize the nematode population in soil.
3. Chemical: Aldicarb, carbofuron, ethoprop have been reported to be effective agains: sugarcane nematode at varied sosages. However, 1.5 kg a.i/ha seems to be moderate dose.