Length, female: 0.40-0.78 mm; length, male: 0.53-0.61
Female: Annules retrorse (200 or fewer, usually
100-150) and visible at low magnification, with smooth or
slightly rough posterior margins, especially towards
tail. Anastomoses rare.
Head broad, first annule entire or emarginated
laterally, sometimes deeply. Submedian lobes well
developed. Lip region conspicuous, elevated. Typically
there are four distinct and well separated labial plates
alternating with the submedian lobes, but this
arrangement varies greatly, fusion between plates
occurring or reduction in their size or number.
Vulva distinctly "open" with lips separated, anterior
lip bearing two protruberances variable in form and
visible only in ventral view. Vagina always sigmoid in
Tail broadly rounded to more
generally a simple rounded or lobed button.
Male: Stylet absent; esophagus indistinct, incapable of
field with four incisures.
Spicules straight to slightly
A large anal tubercle with process is present. Tail
Males often absent.
Juveniles: Posterior margins of annules crenated.
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
Mesocriconema xenoplax has been reported from North and South America, Europe, Africa, India, Australia, and Japan.
This species is found in 38% of California prune orchards and in all of the
four important prune-growing districts and throughout grape-growing regions.
This slow-moving nematode can build
to its highest population levels in highly porous soils, including coarse sands
and well-aggregated silt or clay soils.
Extraction of this nematode from soil is best
accomplished with sugar flotation and centrifugation techniques (Jenkins, 1964).
It is poorly extracted by methods that are useful for other Tylenchida.
Consequently, until development of appropriate extraction techniques, ring
nematode populations were often not detected.
can be expected in any sandy soil where a woody perennial has grown.
However it has a wide host range that includes certain grasses and legumes. In contrast, other ring nematode species of similar size may feed only on grasses
and not on the roots of woody perennials.
All Prunus species, including peach, almond, apricot, cherry,
and plum; also lettuce, carnation, and pine.
Type host - Thompson Seedless grapevine on 1613 rootstock from Fresno
County (Raski 1952).
Vitis vinifera cultivars,
including 'Grenache' and 'Flame Seedless', are among its favored hosts. It is
also hosted well by '3309C' (V. riparia x V. rupestris)
(McKenry and Kretsch, 1994).
The female produces 3-5 eggs/day. The first molt occurs inside the egg.
Observations of egg maturity in 10-12 days at 20-22ÃƒÆ’Ã‚Â¯Ãƒâ€šÃ‚Â¿Ãƒâ€šÃ‚Â½C (Seshadri, 1965) and
hatch in 15 days at 20 C
(Thomas, 1959) are in reasonable accordance with an estimate of 154 + 5
degree days (base 9 C) measured for a South Carolina population (Wescott and
All stages feed and the life cycle is complete in 24 to 30 days.
This nematode has the ability to increase rapidly. It is adversely affected by
low moisture and high soil temperature. Highest population levels are observed
in upper soil in fall-winter with lower populations near the soil surface in
summer. Most of these observations emerge from studies of the nematode on
Population increases at a greater rate on Nemaguard than on Lovell
peach rootstock - (Livingston, California - Ferris et al., 2004).
Nematode is adversely affected by low moisture and high soil
temperatures. Highest population observed in upper soil in fall and
winter; lower population observed near surface of soil in summer.
Damage by this nematode has been most extensively studied on Prunus
spp. and Juglans spp.. It causes pruning and necrosis of fine feeder
roots, especially on young plants, but also feeds on older parts of the root.
predisposes some Prunus spp. and Malus spp. to infection by Pseudomonas
syringae pv syringae, resulting in tree mortality due
(BC) and to winter frost damage. The combined effect of the nematode,
bacterium and cold injury result in enhanced tree mortality in the southeastern
U.S., a condition known as peach tree short-life (PTSL).
Feeding by the nematode results in:
through which M. xenoplax and other stresses predispose Prunus
trees to BC and PTSL remain uncertain; however, evidence is accumulating.
Speculated mechanisms include:
It is important to note that Pseudomonas
syringae (the bacterium) is not in the soil and does not interact
directly with the nematode. It apparently invades the above-ground parts
of the tree at pruning wounds and leaf scars.
In grape, the nematodes feed on young roots, usually
near the root tip, often in large numbers. The feeding results in
local darkening and destruction of the root tissue, and leads to breakdown
of the roots. The root systems of plants attacked by these nematodes
are visibly smaller than those of nematode-free plants. Significant
reductions in top growth can occure (Klingler, 1975).
Mae Nofsinger (former museum scientist, UC Davis) inspects the
Symptoms of bacterial canker include death of shoots and limbs; vascular
discoloration, gummosis, "sour sap," and reduced flower
production. [Note Livingston experiment - no effects of high nematode
population levels on photosynthesis, some vigor decrease, root decrease, - McKenry
observations on pruning of feeder roots].
Plant death does not occur in grapevines, but reductions in vine growth
are observed in sandy areas. On Concord grape (V. labrusca) in
Washington, M. xenoplax stunts vines and causes stunting and
necrosis of feeder roots (Santo and Bolander, 1977). Effects on 'Thompson
Seedless' have been less notable (Raski and Radewald, 1958) but 'Grenache' in
sandy areas appears damaged (McKenry, unpublished data).
Nematode control can be achieved with nematicides (Nemacur -
spp., preplant and postplant nematicides have been important for management of
BC and PTSL. Historically, the postplant nematicide of choice was
1,2-dibromo-3-chloropropane (DBCP) but, following withdrawal of that chemical
from the market, there have been some successes with phenamiphos (Nemacur 3).
In North Carolina, annual fall applications of phenamiphos reduced ring nematode
populations and tree death due to P. syringae (Ritchie, 1984; Ritchie,
1989; Ritchie and Clayton, 1981). Nematicides have been more effective in
reducing PTSL in orchards on Nemaguard rootstock than on the more tolerant
Lovell rootstock (Zehr et al., 1976).
Ferris et al (2004)
found that spring and fall nematicide applications to orchards on both Lovell
and Nemaguard rootstock reduced the the nematode degree-days experienced by the
trees by about 70%. Spring and summer applications of phenamiphos appeared to be
most effective in moderating the rate of increase of M. xenoplax dosage.
That conclusion agrees with observations from many other orchards (M. V. McKenry,
unpublished) and is consistent with reports from the southeast U.S. that
applications of phenamiphos in the spring and fall are more effective in
reducing ring nematode populations than applications in the fall alone (Ritchie,
Host plant resistance has been difficult to find for this
nematode in grapevines. Small
plot work with one population of M. xenoplax indicated that
'Freedom', 'Harmony' and 'Schwarzmann' rootstocks population levels only half as
high as those on V. vinifera cultivars; however, in a field trial
in northern California, 'Freedom' was among the best hosts while 'Harmony' was
Host Plant Resistance, Non-hosts
Attention to soil fertility and irrigation to reduce additional
stresses on plants. Careful pruning to avoid crop overload stress and
prolonged pruning wounds. Avoidance of root injury during
cultivation. Drip irrigation may help to relieve or remove plant stress,
thus increasing plant tolerance of nematode feeding.
The following management plan is a modification of a 10-point plan used
in peach production in the southeastern US. The objectives of such plans
are to integrate stress relief and nematode management components.
Before planting, it is necessary to evaluate the crop history of the
site to determine whether hosts of nematode species of concern (including Meloidogyne spp., Mesocriconema xenoplax, Pratylenchus vulnus and Xiphinema americanum)
have been grown there. Since many of these nematodes have a wide host
range, it is unlikely that all can be avoided, but it may be possible to avoid
several. It would also be important to know of any growth patterns in
previous crops that indicate distribution characteristics of the nematodes or of
their damage. Additional clues to nematode distribution or potential
damage will be provided by assessing soil texture uniformity and patterns in the
field, soil pH, profile characteristics, and nutrient status.
To the greatest extent possible, roots
remaining from a previous crop should be removed from the soil to reduce
nematode and virus reservoirs. The soil should be prepared to reduce
stress on the plants to a minimum, which may enhance their ability to tolerate
any subsequent nematode stress that develops. This process may
include subsoiling or deep plowing to disrupt restrictive layers. Based
upon the site evaluations mentioned above, an irrigation system should be
designed to ensure uniformity and control of delivery, since minimizing moisture
stress on trees may affect their tolerance of nematode stress. From
information on the susceptibility of trees to diseases, such as bacterial canker
in the presence of ring nematodes under certain environmental conditions, it may
be necessary to prepare the site through several of the following procedures:
adjust nutrient and micronutrient status based on soil analysis; raise the soil
pH above 6.5 throughout the soil profile; increase levels of organic matter in
sandy soils; and improve soil structure.
If populations of potentially damaging plant-parasitic nematodes are
found during the site evaluation process, it may be necessary to select another
site. Alternatively, combinations of tactics will be assembled to reduce
population levels of plant parasites, preferably while conserving beneficial
species. One tactic, often costly, is to allow the passage of time with
the field in a fallow condition
since nematode populations decline in the absence of food. Another
approach is to implement a rotations system before planting the orchard and to
avoid planting after crops which may have supported damaging species. In
addition, antagonistic plants and residues, may be used so that nematode populations are suppressed by "allelochemicals."
Several cultural approaches provide some degree of control for certain
nematodes: populations may be suppressed in anoxic conditions created by flooding
the field, and physical disturbance
of soil by repeated cultivation suppresses some
nematode species. Where beneficial organisms are reduced by these
approaches, it may be necessary to re-introduce or augment them prior to
In perennial crops, it is sometimes possible to select a rootstock that
provides desired characteristics without requiring genetic manipulation of the
scion cultivar. Currently, rootstocks such as Nemaguard are available for
stone fruits that confer resistance to root-knot nematodes; however, these
rootstocks appear particularly sensitive to the ring nematode and associated
bacterial canker complex, so they should be selected and used carefully based
upon evaluation of the
site. Rootstocks are not yet available for resistance to the ring or
lesion nematodes, although some sources show promise (Culver et al., 1989;
Another approach would be to select planting stock that is tolerant of the
presence of certain nematodes. For example, the rootstock
"Lovell" appears to confer some tolerance of the ring nematode and
bacterial canker complex, although it is susceptible to root-knot
nematodes. Often, tolerance is determined by prolonged observational
experience; it is difficult to determine experimentally, except in very long and
As technology advances, it may become possible to create transgenic rootstocks
in which genes for resistance to nematodes are derived from other plant
species. An example of potential in this area is with the Mi gene from
tomatoes, although such transgenic plants have not yet been successfully
created. Also interesting is the possibility of introducing a microtoxin
gene into a rootstock.
Having established the orchard, using strategies developed appropriate
for the site, it will be necessary to employ site-specific orchard management
practices that create a superior environment for the trees and, where possible,
an inferior environment for plant-parasitic nematode species. Orchard
management should attempt to maintain adequate soil moisture for the trees and
avoid extreme fluctuations in soil moisture. Avoidance of major and minor
nutrient stress on the trees appears important in boosting their tolerance of
nematode stress and associated problems; foliar and tissue analyses may be used
as a basis for nutrient management. Management of the soil environment to
the advantage of the trees, to the advantage of nematode antagonists, and to the
disadvantage of nematodes, may include monitoring and adjustment of soil
pH and additions of organic matter to the soil. Crop load should be
adjusted in accordance with the age and vigor of the trees by appropriate crop
thinning and pruning practices. Also, there is considerable evidence to
suggest that pruning wounds heal slowly in trees infected with ring nematodes,
thereby exposing the trees to bacterial canker infection. Selection of
pruning times so that wounds will heal rapidly may be important in some
In the established orchard, it will be
important to monitor and manage the status of the plant-parasitic nematode
community. Depending on the expected severity or risk of a nematode
the site, it will be necessary to assess nematode population levels and spatial
pattern, and their probable impact on tree vigor and productivity. As our
understanding of rhizosphere biology improves, it may be very important to
create and maintain an unfavorable biotic environment for plant-parasitic
nematodes by conserving and augmenting biological antagonists in the soil that
exploit nematodes as
a food source, such as fungi and bacteria, or other nematodes of lower
pathogenicity that compete with them, or organisms such as rhizosphere bacteria
that have an antibiotic effect. At present, we only have formative
ideas about how such an antagonist-conducive environment might be created.
Another important emerging area in management of nematode species in orchards is
the use of antagonistic cover crops and their residues. Plants such as
marigolds, and other members of the Compositae, are known to release compounds
into the soil that are toxic to certain nematodes. Studies by McKenry
(1988) suggest that the effect can be enhanced by incorporating the above-ground
parts of these plants into the soil and following with an irrigation to move the
compounds to the nematode target. However, in many cases such plants are
not sufficiently competitive to be grown as cover crops in orchards. Other
plant species show promise but, again, further research is necessary.
Finally, as the development of biorational pesticides continues, it is
important that we encourage the development of materials that may allow
effective nematode management in valuable perennial plantings while constituting
minimal environmental and health hazards. With any such materials, it will
be advantageous to maintain a balanced and buffered soil environment.
Monitoring for, and reintroduction of,
beneficial organisms may also be crucial.
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