Impacts on Crop Protection - Climate Resilient Agriculture for Ensuring Food Security - page 110

changes in population growth rates, increases in
the number of generations, extension of the
development season, changes in crop-pest syn-
chrony, changes in interspecifi c interactions, and
increased risk of invasion by migrant pests (Bale
et al. 2002 ).
Under elevated CO 2 , population densities of
chewing insects are unaffected or decrease, but
do not increase while sap sucker (phloem feeder)
population densities might increase.
A meta-analysis of studies on elevated tem-
perature and elevated CO 2 suggests that insect
herbivore performance is adversely affected by
elevated CO 2 , favored by elevated temperature,
and not modifi ed when both parameters (temper-
ature and CO 2 combined) were elevated.

Climate change due to increased emission of
greenhouse gases is posing a serious challenge to
sustainability of crop production by interfering
with biotic and abiotic components and their
interactions with each other. Global warming
resulting in elevated carbon dioxide (CO 2 ) and
temperature in the atmosphere may infl uence
plant pathogenic nematodes directly by interfer-
ing with their developmental rate and survival
strategies and indirectly by altering host plant
physiology. Severe droughts resulting in a reduc-
tion of soil water will most likely negatively
affect soil nematodes.
Nematode developmental rate is directly infl u-
enced by the temperature with slower develop-
ment at cooler and faster growth rate at warmer
soil temperatures. Therefore, increase in atmo-
spheric temperature due to global warming is
expected to result in more number of generations
per season and expansion of their geographical
distribution range. Other potential effects of ele-
vated temperature on parasitic nematodes include
altered sex ratio, host defense responses, and
interference in their survival strategies like dauer
juveniles or egg diapauses in extreme
environments.
Herbivorous nematodes showed neutral or
positive response to CO 2 enrichment effects with
some species showing the potential to build up
rapidly and interfere with plant's response to
global warming. The number of herbivore, bacte-
rivore, and fungivore nematodes was signifi -
cantly higher under winter wheat and sugar beets
grown under elevated CO 2 (550 ppm), while the
number of carnivore was not changed. The total
numbers of herbivore, bacterivore, and fungivore
nematodes were higher under elevated CO 2 wheat
than under elevated CO 2 sugar beet, most likely
due to the very different root system of both plant
species (Sticht et al. 2009 ).

6.3 Plant Diseases

Climate factors that infl uence the growth, spread,
and survival of crop diseases include tempera-
ture, precipitation, humidity, dew, radiation, wind
speed, circulation patterns, and the occurrence of
extreme events. Higher temperature and humid-
ity and greater precipitation result in the spread
of plant diseases, as wet vegetation promotes the
germination of spores and the proliferation of
fungi and bacteria and infl uences the lifecycle of
soil nematodes. In regions that suffer aridity,
however, disease infestation lessens, although
some diseases (such as the powdery mildews)
thrive in hot, dry conditions, as long as there is
dew formation at night.
Under the warmer-but-drier conditions pro-
jected for North America, crop losses due to plant
diseases are expected to decline as much as 30 %.
However, under the wetter conditions projected
for Africa, losses from diseases will increase by
more than 100 % for some crops.

6.4 Nematodes 6.5 Adaptation and Mitigation

Herbivore nematodes feed on plant parts mostly
on roots. It is estimated that nematodes cause
crop losses worth US$ 125 billion annually in
agriculture (Chitwood 2003 ).

Adaptation refers to an adjustment in natural or
human systems in response to actual or expected
climatic stimuli or their effects that moderate,
harm, or exploit benefi cial opportunities.