Impacts on Plant Pathogens - Climate Resilient Agriculture for Ensuring Food Security - page 158

predicted changes in climate, viral diseases of
plants are expected to increase in importance.
Potentially of greater importance will be the
effects of diseases caused by newly introduced
viruses that, because of the changed climate, will
be able to persist. A warmer climate might also
allow viruses that are present in greenhouses,
such as Pepino mosaic virus (PepMV), to estab-
lish infection in the fi eld. The main effect of tem-
perature in temperate regions is to infl uence
winter survival of vectors. Natural spread of vec-
tors, pests, and diseases is accelerated towards
the north, as former climate barriers are no longer
effective. This results in more severe outbreaks of
plant disease vectors like aphids, whitefl ies,
thrips, or beetles, an extension of the period of
disease infection further into the growing season
and also introduction and establishment of new
vector species. The described effects on vectors
can have severe negative effects on food produc-
tion or result in an increased use of plant protec-
tion products to control the vectors.

spheric water vapor concentrations with increased
temperature that would also favor pathogen and
disease development.
Bacteria are spread to their host plants mainly
by water, usually in the form of rain splash and
insects. In humid, wet conditions, infected plant
tissues can exude masses of bacteria that are
spread from host to host by rain splash and insects.
Therefore, the warmer drier summers expected
with climate change should limit bacterial dis-
eases. However, bacteria often enter hosts through
wounds, and the expected increase in frequency
and intensity of summer storms with high winds,
rain, and hail will increase wounding of plants
and provide moisture for the spread of bacteria.

8.6 Expansion of Geographical

Distribution

With changes in climate, plants will migrate to
new areas, and their pathogens will follow.
How quickly pathogens migrate to follow host
plants will depend on factors such as their dis-
persal mechanisms, suitability of the environ-
ment for dispersal to occur, survival between
seasons, and changes in host physiology and
ecology in the new environment. If a host is
chronically stressed due to less than optimum
conditions, its health would deteriorate and its
susceptibility to disease would increase, par-
ticularly in perennials (Chakraborty et al.
1998 ). New diseases may establish in a region,
while some established diseases may cease to
be economically important. Although climate
changes may reduce the suitability of a crop for
a region, it may continue to be grown for agro-
ecological or economic reasons.
The northward expansion of the soybean sud-
den death syndrome (a soilborne fungal disease
caused by Fusarium solani f. sp. glycines ) is an
example (Roy et al. 1997 ). The disease was fi rst
reported in Arkansas in 1971; in the early 1980s,
it was found in southern Missouri, Illinois, and
Indiana; by the early 1990s, it was also found in
southern Iowa, northern Illinois, and northern
Indiana; and in 1998 it was found in Ontario,
Wisconsin, and Ohio.

8.5 Varying Precipitation

Patterns

Moisture can impact both host plants and patho-
gen organisms in various ways. Some pathogens
such as apple scab, late blight, and several vege-
table root pathogens are more likely to infect
plants with increased moisture - forecast models
for these diseases are based on leaf wetness, rela-
tive humidity, and precipitation measurements.
Other pathogens like the powdery mildew spe-
cies tend to thrive in conditions with lower (but
not low) moisture.
More frequent and extreme precipitation
events that are predicted by some climate change
models could result in more and longer periods
with favorable pathogen environments. Host
crops with canopy size limited by lack of mois-
ture might no longer be so limited and may pro-
duce canopies that hold moisture in the form of
leaf wetness or high canopy relative humidity for
longer periods, thus increasing the risk from
pathogen infection (Coakley et al. 1999 ). Some
climate change models predict higher atmo-