Agriculture Reference
In-Depth Information
not long-lasting, especially if vine planting material is not initially free of nema-
todes or vineyard hygiene is poor. Rootstocks provide the most effective long-term
control of nematodes, although resistance may break down over time. For exam-
ple, in sandy soils in the United States, resistance-breaking strains of
Meloidogyne
species have evolved from the resident soil population some 10 to 20 years after
replanting (Walker and Stirling, 2008).
Table 5.8 summarizes the resistance of common rootstocks to the more
problematic nematode species and strains. Because
V. champini
has a high resis-
tance to the root knot nematode, the rootstock Ramsey became popular in the
Murray-Darling region of Australia.
Muscadinia rotundifolia
, a subgenus of
Vitis
, also has strong resistance to root knot and dagger nematodes, which led to
the breeding of the VR hybrids (vinifera
×
rotundifolia). However, their use in
phylloxera-infested areas is questionable because of their vinifera parentage.
Apart from the use of rootstocks, nematode damage can be mitigated by
good nursery hygiene that ensures cuttings and rootlets are nematode-free and
floor management practices that encourage beneficial nematodes and depress the
population of pest nematodes. In some Australian vineyards a permanent cover
crop has, over time, increased the numbers of predator and omnivore nema-
todes and suppressed pest nematodes (Rahman et al., 2009). Similarly, species of
Brassica
(
B. napus
and
B. juncea
cv Nemfix, known as Indian mustard) produce
compounds called glucosinolates that inhibit pest nematodes. These plants can
be grown as cover crops and slashed before flowering, when the glucosinolate con-
centration is maximal, or cultivated in as green manure. Lowering the pest nema-
tode numbers below the damage threshold, which is about 500 per kg soil for
M. javanica
, may take at least three years of such treatment (Rahman et al., 2012).
Other Rootstock Attributes
■
Salt, Drought, and pH Tolerance
Tolerance of salt and drought has become increasingly important in the choice
of rootstocks, especially as competition for water to grow vines, and hence the
price of water have increased in many inland regions. The threshold salinity
in the root zone above which most
V. vinifera
varieties are affected is electrical
conductivity (
EC
) of 1.8 dS/m, measured as the saturation extract value
EC
e
(see “Soil Testing for Salinity,” chapter 3). As discussed in box 4.11 (chapter 4),
an
EC
e
of 1.8 dS/m is approximately equal to an
EC
dw
of 3.6 dS/m, the latter
being measurable in root-zone solutions obtained with a SoluSAMPLER (see
figure 4.24). Monitoring root-zone salinity is important because wine imported
into the European Union must not contain more than 394 and 606 mg/L of Na
and Cl, respectively. Table 5.9 shows rootstocks that provide varying degrees of
salinity tolerance, essentially through a mechanism of salt exclusion.
