Pratylenchus penetrans

Considered most economic important plant-parasitic nematode in northeastern U.S. Readily spread in bulbs and rooted nursery stock via irrigation water.

An example that characterizes some of the issues regarding migratory endoparasitic nematodes is provided by the root lesion (Pratylenchus penetrans) nematode problem of Easter lily bulbs in a relatively small acreage of northwestern California and southwestern Oregon. Bulblets, usually picked from a previous crop, are field-grown for 2 to 4 years until the bulbs are large enough to sell to greenhouse operations for production of flowering plants. Feeding by Pratylenchus penetrans on the roots retards the rate of growth of bulbs and extends the time necessary for them to achieve the 20-cm circumference used as a basis for marketing. If bulbs have not reached 20 cm circumference in two years, they are replanted for one or two more years (Hawkins, 1991; Westerdahl et al., 2003). Further, nematodes in root tissues attached to bulbs are readily distributed throughout the state.

Avoidance of the lesion nematode problem in Easter lilies by crop rotation or planting site selection is difficult. The nematode has a very wide host range and is supported by the pasture grasses that are commonly grown as an alternative to bulb production. Many nematicides have been tested for nematode control in the region and several have resulted in groundwater contamination. The current standard soil treatment for management of P. penetrans in the region is a preplant application of 1,3-dichloropropane (Telone II) at 428 kg/ha and 9 kg/ha of Phorate applied at planting. Preplant drip applications of metam sodium or emulsifiable 1,3-dichloropropene in combination with oxamyl or metalaxyl show promise as a means of reducing the total amount of chemical applied to soil and reducing the risk of groundwater contamination (Westerdahl, et al. 2003).

Potato Early Dying Disease is caused by Verticiliiunm dahliae and exacerbated through interaction with P. penetrans. The effect of the nematode may be to:

Although Verticillium and Pratylenchus are considered the main causal agents in some potato growing areas of North America, other pathogens such as the bacterium Erwinia and the fungus Colletotrichum coccodes are associated with symptoms similar to Potato Early Dying Disease.

Feeding:

Migratory endoparasite, mainly in root cortex but may enter vascular tissues in later stages of infection.

Hosts:

Pest of lily bulbs (grown on 300 acres for bulb production) in Del Norte County, CA.

For an extensive list of host plant species and their susceptibility, copy the name

Life Cycle:

Damage:

Necrotic lesions on peach roots after 24 hours. Symptoms of debilitation above ground, including chlorosis and twig die-back. Damage is increased by interaction with fungi.

Peach roots contain amygdalin (a cyanophoric ß-glucoside - essentially a complex sugar with a cyanide molecule attached). Amygdalin is a common constituent of Prunus spp., and is thought to be hydrolyzed during a series of molecular events initiated by the plant in response to invasion. The hydrolysis products of amygdalin are hydrogen cyanide and benzaldehyde which are phytotoxic and result in cell death.

In a classical study, Mountain and Patrick (1959) found no amygdalin in root lesions associated with P. penetrans; they concluded that it is hydralyzed as either the plant invokes the defense mechanism against P. penetrans or that the nematode initiates the hydrolysis. They also found that necrosis and cell death in the root tissue occurs rapidly following root invasion by the nematode and that it occurs in advance of the invading nematode. An interpretation of thes observations in light of current understanding of plant defense mechanisms is that the plant is recognizing damage associated moleccular patterns (DAMPs) or parasite/pathogen-associated molecular patterns (PAMPs) and initiating defenses that result in cell death in advance of the invading nematode. In their studies, Mountain and Patrick (1959) found that the necrosis could be initiated by the nematode alone and did not require the presence of fungi or bacteria, but that an imprtant contributor to peach replant problems by the nematode was that root degeneration was accelerated by the infection courts for fungi and bacteria that were provided by the damage.

Effect of different population densities of Pratylenchus penetrans on growth of onions (0, 666, 2,000, 6,000, 18,000 nematodes/Kg soil) (Canada).

Damage to lily bulb in Del Norte County is a reduction in the rate of growth. Consequently, bulbs require two years to reach marketable size rather than one year. Further, harvested bulbs are infested with the endoparasitic nematode and will be transported to new sites.

Management:

Nematicides are effective on soil populations, but have resulted in groundwater pollution in the sandy soils of Del Norte County.

Hot water treatment at 45.5 C for 15 to 20 min kills the nematode in apple roots, 48 C for 10 min in strawberry roots. Hot water dips are also used to treat harvested lily bulbs, but the difference between temperatures that kill nematodes an temperatures that cause damage to flower bud primordia is quite small. Temperature regulation is critical.

Crop residues and organic amendments reduce populations in apple orchards, either by breakdown products or by encouraging growth of nematode-trapping fungi.

Treatment Thresholds. Severity of Potato Early Dying is related to the inoculum levels of fungus and nematode prior to planting. Damage threshold levels are Verticillium > 4 propagules /gm of dry soil in the absence of P. penetrans and 2 propagules/gm dry soil in the presence of P. penetrans

For a list of plant species or cultivars (if any) reported to be immune or to have some level of resistance to this nematode species, copy the name

References:

Hawkins, L. 1991. IPM options for Easter lily bulb production: An overview. California Department of Food and Agriculture. PM91-2.

Mountain, W.B. and Patrick, Z.A. 1959. The peach replant problem in Ontario: VII Pathogenticity of Pratylenchus penetrans (Cobb, 1917) Filip. & Stek. 1941. Canadian Journal of Botany 37:459-470.

Westerdahl, B.B., D. Giraud, S. Etter, L.J. Riddle, J.D. Radewald, C.A. Anderson, and J. Darso. 2003. Management options for Pratylenchus penetrans in Easter lily. Journal of Nematology 35:443-449.

Pratylenchus penetrans	Contents	Rev 12/06/2012
	Classification	Hosts
	Morphology and Anatomy	Life Cycle
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