Agriculture Reference
In-Depth Information
Table 8.2 Possible effects of climate change on plant-pathogen survival
Common types of
pathogens
Survival mode of pathogen
Effects of climate change
Disease organisms that survive
in soil
Introduced diseases
Thick-walled spores and other survival structures produced
by these pathogens should not be greatly affected by
climate change
Disease organisms that survive
in plants or plant debris
Introduced diseases
Milder winters could increase survival of pathogens that
overwinter on living and dead plants
Disease organisms that are
transferred by vectors
Viruses and fungi
Milder winters could increase survival of insect vectors;
milder summers could result in increased development and
reproductive rates
Introduced diseases
Introduced diseases
Pathogens that do not presently survive winters may do so
if winters become milder
• Increases in pathogen development rate, trans-
mission, and generations per year
• Increases in overwintering of pathogens
• Changes in host susceptibility to infection
Furthermore, they suggested that the most
severe and unpredictable consequences would
occur if populations of pathogen and host, which
were formerly geographically separated due to
climate constraints, converged.
Long and cold winters have reduced survival
of organisms that cause disease, restricted the
number of disease generations per year, and lim-
ited disease activity during the growing season. If
the climate warms, these issues of disease sur-
vival, growth, and activity will change. For dis-
ease survival, climate change effects will depend
on the way in which the pathogen presently sur-
vives adverse conditions (Table 8.2 ).
Increases in temperature can modify host
physiology and resistance. Both temperature and
the length of exposure are important in determin-
ing the effect of climate change on disease sever-
ity. Even if the temperature change may be well
within the limits of current climatic variability, a
modest warming can cause a signifi cant increase
in cumulative temperature above a critical tem-
perature threshold to affect crop physiology and
resistance to a disease. Temperature change
might lead to appearance of different races of the
pathogens hitherto not active but might cause
sudden epidemic. Change in temperature will
directly infl uence infection, reproduction, disper-
sal, and survival between seasons and other criti-
cal stages in the life cycle of a pathogen.
At higher temperature, lignifi cation of cell
walls increased in forage species and enhanced
resistance to fungal pathogens. Impact would,
therefore, depend on the nature of the host-
pathogen interactions and mechanism of resis-
tance. A rise in temperature above 20 °C can
inactivate temperature-sensitive resistance to
stem rust in oat cultivars. Increase in temperature
with suffi cient soil moisture may increase evapo-
transpiration, resulting in humid microclimate in
crop canopy, and may lead to incidence of dis-
eases favored under warm and humid conditions.
Some of the soilborne diseases may increase at
the rise of soil temperature. If climate change
causes a gradual shift of cropping regions,
pathogens will follow their host. Analysis of
long-term data of wheat and rice diseases in
China has shown trends of an increase in mini-
mum temperatures in association with the abun-
dance of rice blast or wheat scab. In most
locations, temperature changes had signifi cant
effects on disease development. However, these
effects varied between different agroecological
zones. In cool subtropical zones such as Japan
and northern China, elevation of ambient tem-
perature resulted in greater risk of blast epidem-
ics. Situations in the humid tropics and warm
humid subtropics were opposite to those in cool
areas. A lower temperature resulted in greater
risk of blast epidemics.
Temperature has potential impacts on plant
disease through both the host crop plant and the
pathogen. Research has shown that host plants
such as wheat and oats become more susceptible
 
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