Pratylenchus vulnus		Contents		Rev 10/10/2006
		Classification		Hosts
		Morphology and Anatomy		Life Cycle
Return to Pratylenchus Menu		Economic Importance		Damage
		Distribution		Management
Return to Pratylenchidae Menu		Feeding		References
Access P. vulnus Theme Music		Go to Nemaplex Home Page

Classification:

      Tylenchida
       Tylenchina
        Tylenchoidea
         Pratylenchidae
          Pratylenchinae
           Pratylenchus vulnus

Root Lesion Nematode

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Morphology and Anatomy:

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Distribution:

California.

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Economic Importance:

C-rated pests in California.

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Feeding:

Migratory endoparasite.

Feeds mainly in cortex; may penetrate xylem, but rarely the phloem.    

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Hosts:

Over 80 hosts, including fruits, nuts, peaches, grapevines, soybeans and others.

Many hosts are woody perennials.

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Life Cycle:

Males and females are present.

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Damage:

Smaller roots may be killed by nematode feeding.
	Carignane grape roots grown in soil from a walnut orchard infested with P. vulnus (left); in same soil treated with 1,3-D nematicide (right).

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Management:

Nematicides:  Preplant treatment of 1,3-Dichloropropene (1,3-D) followed by 2.5 gal/acre DBCP annually in tree crops was very effective, however DBCP is no longer available. Postplant treatments with Nemacur (phenamiphos) can be effective.

Hot water treatments: (5 min at 51.7 C) eradicates this species from grapevine roots.

Tolerant Rootstocks:  Some walnut rootstocks are reputed to show tolerance. e.g., hybrids of Juglans hindsii and Juglans regia - cv Paradox.  

Myrobalan 29C plum rootstock appears more tolerant to P. vulnus than Lovell peach rootstock.	Plum on Myrobalan 29C rootstock (left) and on Lovell rootstock (right) in soil infested with P. vulnus.   Experiment by M.V. McKenry at Kearney Agricultural Center, Parlier, California.

Resistant Rootstocks: There is a large rootstock screening and development program at the USDA Fresno station for resistance and tolerance to P. vulnus (Dr. Craig Ledbetter).

The Paradox diversity study recognizes that Paradox hybrids (J. regia x J. hindsii hybrids are all genetically different seedlings.  Some may be more resistant or tolerant than others to P. vulnus.  The hybrids are sterile, so if useful rootstocks are found in the project, the development of vegetative propagation will be critical.

Consider transgenic options with rootstocks:
Mycogen corp. (San Diego) reportedly isolated Bacillus thuringiensis (Bt) strains effective against Pratylenchus spp. and later transferred the rights to Monsanto Corporation.  The Bt gene responsible for toxin production effective against certain insect pests has been transgenically inserted into the genome of some plants; a similar strategy would probably work against nematodes with the nematode-effective Bt gene.  The toxic crystal molecules coded by the Bt gene are large; they range in molecular mass from 40 to >70 kDa (Wei et al, 2003).  Crystals would need to be ingested by the plant-feeding nematode and there has been some speculation that stylet-aperture exclusion would be a problem.  However, Meloidogyne incognita, Globodera rostochiensis and Rotylenchulus reniformis are able to ingest green flourescent protein molecules of >28 kDa size from plant cells (Goverse et al, 1998; Urwin et al, 1997; Urwin et al, 2000).  The size of the Bt crystal is 40-70 kDa and there is currently no evidence to suggest that crystals of that size would be excluded by the stylet aperture. The inability of Heterodera schachtii to digest proteins >40 kDa has been attributed to the a zone of exclusion established in the cytoplasm when these nematodes feed in plant cells (Bockenhoff and Grundler, 1994; Urwin, et al, 1997).

Researchers at the University of California attempted to obtain the nematode-effective Bt gene from Monsanto for development of transgenic walnut rootstocks.  However, the walnut nursery market was considered too small by industry to justify costs of development.  Research efforts have been focused on large-acreage crops but the Monsanto Corp. abandoned this approach for lesion nematodes in cotton in the late 1990s.

Other potential transgenic approaches:  Chitinase genes (only effective against eggs?)- Dr. Gale McGranahan, (Pomology, UC Davis).
Snowdrop lectin - Dr. Dandekar (Pomology, UC Davis)
Studies with trichosanthin (ribosome inhibiting protein).

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References:

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Copyright © 1999 by Howard Ferris.
Revised: October 10, 2006.