americanum Cobb, 1913
Has same general configuration as female. Actually, males of X.
americanum are seldom found.
testes, with one branch anterior and one branch
posterior, around mid body. Connected to
cloaca through seminal
vesicle and vas deferens.
Vulva region and tail region.
Female is diovarial and amphidelphic.
Vulva at 46-54% of body length.
Xiphinema americanum is actually considered to be a
group of some 39 species, which include X. brevicolle and X.
Molecular techniques are further underscoring the
variability within the group and adding to the body of knowledge that
will be required for an eventual taxonomic revision (Vrain,
The group also includes X.
californicum which is probably associated with grape in
California (Lamberti and Ciancio, 1993).
group. Adult stages of this nematode range in length from 1.3 to
2.2 mm. However, the X. americanum sensu stricto
ranges from 1.6 to 1.8 mm in length with an odontostyle
length slightly greater then 100 Âµm .
The morphometrics of
these species tend to overlap (Robbins and Brown, 1991).
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
It is currently suggested that the true X.
americanum is native to, and predominant in, the eastern U.S. whereas the
western U.S. populations are actually X. californicum, X. pacificum
and other species (Lamberti and Bleve-Zacheo, 1979). Although true X. americancum
occurs in California it may not be as common as X. californicum.
Members of the X. americanum
group are common throughout vineyard areas of California, with the notable
exception of the drier and warmer Coachella Valley (Siddiqui et al., 1973).
They are most numerous in vineyards with abundant other vegetation, usually
those in areas with >45 cm annual rainfall.
Migratory root ectoparasite; all stages feed at root tips.
Deep penetration of root tip by stylet; causes hypertrophy of cells, wall
Causes necrosis of feeder roots on strawberries.
Species in this group of nematodes are
difficult to study biologically because they are not readily cultured in
greenhouse or laboratory conditions. They have a wide host range that includes
common weeds and grasses, strawberries, and soybeans, forest trees
(spruce, pine, etc.), perennial orchards, grape. 90% of California pear
orchards (French, 1964).
The breadth of the host range is probably also related to the genetic
diversity within the species complex.
Four larval stages were thought to occur in the soil as there is no molt in
the egg. However, recent studies indicate that some members of the X.
americanum group (including X. americanum sensu
stricto and X. californicum) pass through only three juvenile stages
before becoming adults (Halbrendt and Brown, 1992).
Molting does not occur in the egg and the first stage hatches.
The length of the life cycle has not been experimentally determined;
speculated to be 1 year (Malek, 1969). However, two population peaks are
sometimes observed per year, although not in our (Ferris and McKenry,
1974) studies in
California. Current conventional wisdom is that the
longevity of X. americanum individuals is 3 to 5 years, with
only one generation produced per year (Halbrendt and Brown, 1993).
Research experience and
conventional wisdom has been that X. americanum is difficult to
culture in pots under greenhouse conditions (Cohn and Mordechai, 1969,
Lownsbery and Mitchell, 1965), which may have deterred researchers from
attempting to work with the nematode under controlled conditions. The
earlier work suggested that maintenance of relatively constant moisture
conditions was important (Lownsbery and Mitchell, 1964) and more recent
studies suggest that regulated temperature conditions are favorable for
the nematode and that sorghum and grasses are useful greenhouse hosts
(Diop et al., 2001). The temperature and moisture conclusions are quite
interesting because, under field conditions in California vineyards,
X. americanum is most prevalent in the upper 30-45 cm of soil where
aeration conditions are favorable but soil moisture and temperature
conditions fluctuate the most (Ferris and McKenry, 1974).
Palomeres-Rius et al (2016) screened 124 plant-feeding nematode populations
for the presence of bacterial endosymbionts; that is, bacteria living within the
body of the nematode. Potential bacterial endosymbionts were only
detected in species of Xiphinema, particularly in species of the X.
americanum (sensu lato) group.
One group of 16S rRNA sequences was related to ‘Candidatus Xiphinematobacter’
and a second to the bacterial family Burkholderiaceae, which includes fungal
and plant endosymbionts.
The study suggests a highly specific symbiotic relationship and a high degree
of phylogenetic congruence and long-term evolutionary association between hosts
The bacterial endosymbionts are transmitted vertically to progeny. They
are observed to colonize the ovary wall of females of Xiphinema
species, they apparently invade developin oocytes and are seen in
uninucleate eggs in the uterus. They become associated with intestinal
epithelium during nemattode development and then with the overy in adult females
(Palomares-Rius, 2016; Vandekerckhove et al., 2002; Brown et al., 2015).
Endosymbionts may have effects that range from parasitism (harmful to the
host), through commensalism (neutral effects) to mutualism (beneficial to host
and enosymbiont). The effects of the realtionships between the
endosymbionts and Xiphinema spp. is unknown at this time)s. In
the latter case, both host and endosymbiont would benefit from the
realtionship.Although the nat
There are other examples of bacterial endosymbionts in nematodes. In
many cases their roles in the biology of the nematode are unknown
(Palomares-Rius et al, 2016), for example:
Associations between the insect-pathogenic bacteria
Photorhabdus and Xenorhabdus is necessary for completion of the life cycle
of Heterorhabditis and Stienernema (Ruby. 2008).
Detection of Wolbachia in the burrowing nematode
Radopholus similis and R. arabocoffeae (Haegeman, et al.
Verrucomicrobia has been detected in theXiphinema
americanum group (Vandekerckhove et al., 2002).
Bacteroidetes has been detected in populations
of Heterodera glycines and Globodera rostochiensis (Noel &
Nematode causes root stunting and tip galling.
It causes necrosis on strawberry roots. It is also common in declining
vineyards at high population densities. Marked growth response in
grapevines were obtained after applications of DBCP.
From field observations, certain
populations identified as X. californicum can build to 4-5 times
the population level of a typical X. americanum sensu stricto.
Population levels of X. americanum sensu lato in excess of
500 actual individuals/250 cm3 in non-weedy sites should be suspected as a
probable cause for vine damage (McKenry, 1992).
Xiphinema americanum is a NEPO virus
vector - polyhedral particles.
Xiphinema americanum sensu lato vectors:
Populations within the X. americanum
group are capable of transmitting various strains of tomato ringspot virus (TRSV):
However, some populations keyed to the
same species may not be able to transmit the virus (Brown et al., 1993).
Virus particles can be acquired within 24 hours of exposure to root.
They occur in the esophageal lumen near stylet extension and in the glandular
region of the esophagus.
In California, TRSV strains have not posed serious production problems in
grape vineyards like those due to grapevine fanleaf virus. This could be a
direct result of quarantines on virus infected grape cultivars. Vine damage
attributable to the nematode alone is not great. At high inoculum levels, there
was significant damage to newly planted 'French Colombard' in one experiment
but not in others. Damage may occur when other factors also reduce root systems
or force a shallow root system (Ferris and McKenry, 1975).
Some conventional grape rootstocks
tested by McKenry
in California have shown some resistance
to X. americanum
sensu stricto include 'VR-O39-16', 'Freedom', 'Dog Ridge', and 'Schwarzmann'
(McKenry and Kretsch, 1994).
contrast, V. vinifera and '1613C' are good hosts. In vineyards,
'VR-O39-16' and 'Freedom' do build-up populations of X. americanum
sensu lato, however.
Host Plant Resistance, Non-hosts
CIH Descriptions of Plant-parasitic Nematodes,
Set 2, No. 29 (1973).
Cohn E., and Mordechai, M. 1969.
Investigations on the life cycles and host preference of some species of
Xiphinema and Longidorus under controlled conditions. Nematologica
Diop, M.T., DiÃƒÂ©mÃƒÂ©, J-H., Mountport, D. and Baujard,
P. 2001. Laboratory culture of two Xiphinema americanum-group
species (Nematoda: Longidoridae) from Senegal. Nematology 3:411-415.
Ferris, H. and M. V. McKenry. 1974.
Seasonal fluctuations in the spatial distribution of nematode populations
in a California vineyard. Journal of Nematology 6:203-210.
Lownsbery, B.F. and Mitchell, J.T. 1965. Some effects of
chemical amendments and cultural conditions on population levels of Xiphinema
americanum. Pl. Dis. Reptr 49, 994-998.