Impact of Climate Change on Plant-Associated Fungi
89
disease on a wide range of host plants whereas other pathogens can only infect a
narrow range of closely related plant species. Likewise, host defense responses can
range from non-specific stress-induced responses to very specific reactions based on
the presence of specific genes in both the host and pathogen.
Concentrations of CO 2 and O 3 have increased since the initiation of the industrial revolution, and they will continue to increase in the 21st century. It is well
known that both elevated CO 2 and O 3 change plant function like photosynthetic
capacity, water-use capacity and growth of the crop. These parameters are increasing
with increasing CO 2 , but are reduced by increasing O 3 . These responses of plants
to climate change also affect the host-pathogen interactions. Improved photosynthetic proficiency under increased CO 2 provides additional carbohydrate that results
in increasing starch and sugar levels in leaf tissue. Under elevated O 3 , levels of
starch and sugar decrease. Enrichment of sugar content of leaves of plants enhances
the sugar-dependent pathogens. The negative effects of increased O 3 on plant physiology, growth and yield lead to decreased photosynthetic capacity that results in
visible lesions, decreased leaf durability and premature leaf [23].
CO 2 concentrations affect several rust diseases of cereal crops. Infections by
Puccinia coronata on oats, Puccinia dispersa on rye, and Puccinia graminis f.sp.
tritici and Puccinia recondita f.sp. tritici on wheat were all enriched by concentrations
of CO 2 in the 0.5–0.75% average [24]. Interestingly, soybean downy mildew, caused
by Peronospora manshurica, another biotroph, decreased under increased CO 2 level
than on those grown with ambient levels of CO 2 [23]. As this pathogen infects
through stomata, increased CO 2 levels decreased the number of stomates per unit
leaf area thereby providing less infection sites. Higher CO 2 levels also reduced the
time that stomata were open, which lead to a reduction of the degree of infection.
Increased CO 2 levels. However, lead to increased colony formation of the powdery
mildew pathogen. These suggest that there are different mechanisms through which
CO 2 levels regulate plant infections caused by biotrophic pathogens.
Soybean plants under elevated CO 2 grew faster than those in the ambient CO 2 and
were infected by the necrotroph, Septoria glycines, the causal agent of the brown
spot over the growing season [23]. Rice plants grown under increased CO 2 conditions showed an increased susceptibility of the leaf to the sheath blight disease.
Wheat plants under elevated CO 2 levels demonstrated increased plant biomass as
well as increased biomass of the fungal pathogen, Fusarium pseudograminearum,
that causes crown rot in plants [13, 12]. These studies all support the idea that
increased CO 2 levels enhance greater plant growth, which in turn, lead to increased
disease levels of necrotrophic pathogens.
Increased CO 2 level reduced leaf necrosis in potato (late blight of potato) caused
by Phytophthora infestans infection [23]. This was attributed to increased β-1,3glucanase activity under increased CO 2 levels, this enzyme plays a role in disease
resistance. The greatest levels of resistance were observed when CO 2 was significantly higher, and O 3 concentration was significantly lower than the ambient concentration. As O 3 levels increased to one or two times the ambient level, the positive
effects of CO 2 decreased. Starch and soluble sugars increased in the leaves, and
89
disease on a wide range of host plants whereas other pathogens can only infect a
narrow range of closely related plant species. Likewise, host defense responses can
range from non-specific stress-induced responses to very specific reactions based on
the presence of specific genes in both the host and pathogen.
Concentrations of CO 2 and O 3 have increased since the initiation of the industrial revolution, and they will continue to increase in the 21st century. It is well
known that both elevated CO 2 and O 3 change plant function like photosynthetic
capacity, water-use capacity and growth of the crop. These parameters are increasing
with increasing CO 2 , but are reduced by increasing O 3 . These responses of plants
to climate change also affect the host-pathogen interactions. Improved photosynthetic proficiency under increased CO 2 provides additional carbohydrate that results
in increasing starch and sugar levels in leaf tissue. Under elevated O 3 , levels of
starch and sugar decrease. Enrichment of sugar content of leaves of plants enhances
the sugar-dependent pathogens. The negative effects of increased O 3 on plant physiology, growth and yield lead to decreased photosynthetic capacity that results in
visible lesions, decreased leaf durability and premature leaf [23].
CO 2 concentrations affect several rust diseases of cereal crops. Infections by
Puccinia coronata on oats, Puccinia dispersa on rye, and Puccinia graminis f.sp.
tritici and Puccinia recondita f.sp. tritici on wheat were all enriched by concentrations
of CO 2 in the 0.5–0.75% average [24]. Interestingly, soybean downy mildew, caused
by Peronospora manshurica, another biotroph, decreased under increased CO 2 level
than on those grown with ambient levels of CO 2 [23]. As this pathogen infects
through stomata, increased CO 2 levels decreased the number of stomates per unit
leaf area thereby providing less infection sites. Higher CO 2 levels also reduced the
time that stomata were open, which lead to a reduction of the degree of infection.
Increased CO 2 levels. However, lead to increased colony formation of the powdery
mildew pathogen. These suggest that there are different mechanisms through which
CO 2 levels regulate plant infections caused by biotrophic pathogens.
Soybean plants under elevated CO 2 grew faster than those in the ambient CO 2 and
were infected by the necrotroph, Septoria glycines, the causal agent of the brown
spot over the growing season [23]. Rice plants grown under increased CO 2 conditions showed an increased susceptibility of the leaf to the sheath blight disease.
Wheat plants under elevated CO 2 levels demonstrated increased plant biomass as
well as increased biomass of the fungal pathogen, Fusarium pseudograminearum,
that causes crown rot in plants [13, 12]. These studies all support the idea that
increased CO 2 levels enhance greater plant growth, which in turn, lead to increased
disease levels of necrotrophic pathogens.
Increased CO 2 level reduced leaf necrosis in potato (late blight of potato) caused
by Phytophthora infestans infection [23]. This was attributed to increased β-1,3glucanase activity under increased CO 2 levels, this enzyme plays a role in disease
resistance. The greatest levels of resistance were observed when CO 2 was significantly higher, and O 3 concentration was significantly lower than the ambient concentration. As O 3 levels increased to one or two times the ambient level, the positive
effects of CO 2 decreased. Starch and soluble sugars increased in the leaves, and