Agriculture Reference
In-Depth Information
Table 9.4
Effect of temperature on root growth and infestation of grapevine rootstocks by
Meloidogyne javanica
Jacquez
143 B Mgt
Treatment
Galling
1
Egg sacs
2
Egg
3
Galling
1
Egg sacs
2
Eggs
3
A. 23 °C/44 days
(572DD
1O
)
16.2 a
5.2 a
460 a
1.2 a
0.0 a
0 a
B. 23 °C/178 days
(1014DD
1O
)
62.6 ab
22.2 a
560 a
2.0 a
2.0 a
75 a
C. 33 °C/44 days
(1012DD
1O
)
41.2 ab
14.6 a
464 a
66.6 ab
16.6 a
396 b
D. 33 °C178 days
(1794DD
1O
)
613.2 b
613.2 b
855 b
230.6 b
220.6 b
825 b
Treatments which differ signifi cantly (P
0.05) are marked vertically with different letters
DD
1O
Physiological time expressed as degree days above a predetermined threshold of 10 °C
1
Galling is expressed by the number of galls visible per 5 g of new roots under 20× magnifi cation
2
Egg sacs are expressed by the number visible per 5 g new roots under 20× magnifi cation
3
Eggs are the average number calculated per egg sac
≤
higher temperature. Chitambar and Raski (
1984
)
also found that the grapevine rootstock cultivars
Harmony and Couderc 1613 lost their resistance
at 36 °C.
Various stages in the soybean cyst nematode
(SCN) disease cycle are affected differentially
by temperature and moisture. The highest win-
ter survival of SCN eggs occurs in the colder
areas of the continent. Thus, spring inoculum
levels may be highest in the northern range of
soybean culture. Optimal soil temperatures for
egg hatch, root penetration, and juvenile and
adult development are 24 °C, 28 °C, and
28-32 °C, respectively; below 15 °C and above
35 °C, little development occurs. Thus, temper-
ature can affect the number of SCN generations
per growing season. In theory, with fewer gen-
erations, new races will develop less quickly.
The more moderate winter temperatures will
reduce egg survival, while the higher tempera-
tures in the growing season will increase egg
hatch, the rate of nematode development, and,
perhaps, the number of generations per season.
Soil water is important for SCN movement and
development, but water is unlikely to be a limit-
ing factor early in the season. More importantly,
the drier growing conditions of summer will
increase the yield loss due to SCN because of
reduced root surface.
While the exact cause of the recent alfalfa
stem nematode outbreak in Yolo County is
unclear, an increase in winter temperatures is
likely to be an important contributing factor.
Stem nematodes do not actively reproduce below
41 °F. In Yolo County, average minimum winter
temperatures have increased 3 °F since 1983 and
are currently approaching the lower reproductive
threshold (Fig.
9.3
). Higher temperatures allow
the nematode to complete a larger number of
breeding cycles during the winter and thus impact
the severity of the infestation. If climate change
causes winter temperatures to rise further, out-
breaks of alfalfa stem nematode may become
more frequent in the region. Additionally, the use
of organophosphates and carbamate in alfalfa
crops has decreased 50 % since 2005. These
pesticides are known to suppress stem nematode
populations, but are being replaced by pyre-
throids, which do not affect the stem nematodes.
Consequently, the decreased use of these pesti-
cides may have also played a role in the recent
outbreak.
9.5
Expansion of Geographical
Distribution
Boag et al. (
1991
) used data from soil samples
collected during the European plant-parasitic
nematode survey to assess the possible impacts
of climate warming on the geographical range of
virus-vector nematodes. Initial analyses of nema-
tode presence-absence data suggested a close
association between mean July soil temperature
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