Agriculture Reference
In-Depth Information
Nematodes
7.3.3.2
Nematodes are small, nonsegmented roundworms that feed on other soil mi-
croorganisms or on plant roots. The latter are parasitic nematodes, of which a
range of species feed on vine roots, causing malformations and necrosis. Infested
vines suffer reduced root function and loss of vigor, without any specific above-
ground symptoms. Nematode damage is more severe in sandy soils. Overall, ne-
matodes are a more serious problem than phylloxera in Australian vineyards. The
most common nematodes in vineyard soils are outlined here.
Root-knot Nematode ( Meloidogyne species). These nematodes have a very
broad host plant range and are widespread in Australia, especially in the sandy
soils of Sunraysia and the Riverland. At least four species— M. incognito . M. ja-
vanica , M. arenaria , and M. hapla —are serious pests of grapevines in different re-
gions of the world. The organism is endoparasitic, with the juveniles hatching
from eggs in the soil and invading just behind the root tip. The cells of the root
cortex swell to form a gall, typically ca. 3 mm in diameter, in which the females
breed and lay eggs. A single gall with a succession of females may survive for sev-
eral years. Cover crop species act as alternate hosts for these nematodes.
Root-lesion Nematode ( Pratylenchus species). Many species of Pratylenchus are
found in vineyards, but the most common is P. vulnus . The organism is en-
doparasitic: It does not produce galls on the roots, but migrates through the tis-
sues and impairs vine growth. The lesions formed can predispose the roots to in-
vasion by fungal pathogens such as Phytophthora (section 7.3.3.4).
Dagger Nematode ( Xiphinema species). These organisms are large and ec-
toparasitic. They migrate through the soil to feed on vine roots, causing swelling
of the root tips. The most common species in vineyards worldwide is X. index ,
but X. americana also occurs. The former also transmits the Grape Fanleaf Virus
(GFLV), which causes problems in vineyards of the North Coast, Napa, and Cen-
tral Valley of California, and in Northeast Victoria. If a vineyard has both the ne-
matode and the virus, the only effective control is to remove the vines and not
replant for 10 years.
Citrus Nematode ( Tylenchulus semipenetrans ). This nematode feeds ec-
toparasitically on root cells. It is restricted to a few plant genera—importantly,
citrus and grapevines—and is common in the Sunraysia and Riverland districts of
southeastern Australia where these two crops are commonly grown in close asso-
ciation.
Use of Rootstocks. Resistant rootstocks are the most effective means of nema-
tode control. The species V. champini has high resistance to root-knot nematodes,
which led to selection of the rootstocks Ramsey and Schwarzmann in Australia.
In California, the rootstocks Dogridge, Harmony, and Freedom are favored for
their nematode resistance, but the phylloxera resistance of the latter two is ques-
tionable.
Muscadinia rotundifolia , a subgenus of Vitis , has strong resistance to root-knot
and dagger nematodes, which has led to the breeding of the VR hybrids ( vinifera
rotundifolia ). However, their use in phylloxera-infested areas is questionable be-
cause of their V. vinifera parentage. Further details on the range of resistant root-
stocks available are given in the review by Nicol et al. (1999).
Apart from the use of resistant rootstocks, nematode damage can be miti-
gated by good nursery hygiene that ensures cuttings and rootlets are nematode-
free (see appendix 13), and any practice that improves root growth and nutrient
 
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