Impacts on Plant Pathogens - Climate Resilient Agriculture for Ensuring Food Security - page 154

Fig. 8.3 Cumulative
number of lesions ( a ) and
disease severity expressed
as percent leaf area
affected ( b ) caused by
Colletotrichum gloeospori-
oides on susceptible
Stylosanthes scabra plants

content at elevated CO 2 was similar to that of
ambient CO 2 , but N content was signifi cantly
reduced. As a consequence, severity of powdery
mildew caused by Erysiphe graminis infection
was signifi cantly reduced, compared to ambient
CO 2 . At lower water supply (1.8 mm/day), the
results were quite different. Host water content
at elevated CO 2 was higher compared to that of
ambient CO 2 , but N content showed no differ-
ence. As a consequence, severity of powdery
mildew infection was signifi cantly increased,
compared to ambient CO 2 . It seems that severity
of mildew infection is more sensitive to host
water content than to host nitrogen content
(Thompson et al. 1993 ).
Astonishing results were gained in an experi-
ment on oat ( Avena sativa ) grown under elevated
CO 2 (700 ppm) and infected by barley yellow
dwarf virus (BYDV). Root mass of virus-infected
plants increased by 37-60 % with CO 2 enrich-
ment but was largely unaffected in healthy plants.
CO 2 enrichment increased photosynthesis and
water-use effi ciency by 34 and 93 % in healthy
plants and by 48 and 174 % in infected plants -

under elevated CO 2 than at ambient CO 2
(Malmstrom and Field 1997 ).
Chakraborty et al. ( 2000a , b ) studied dispersal
of and infection by Colletotrichum gloeosporioi-
des under ambient weather conditions in the fi eld
on Stylosanthes scabra plants that had been
raised under 1x or 2xCO 2 in controlled environ-
ment chambers. Plants from the two CO 2 envi-
ronments were exposed to naturally occurring
inoculum in the fi eld on different dates, and
conidial dispersal and infection were monitored.
The enlarged canopy of plants grown under
elevated CO 2 trapped more conidia that, together
with increased humidity in the denser canopy, led
to more severe anthracnose than on plants grown
under 1xCO 2 (Fig. 8.3 ).
Decomposition of plant litter is important for
nutrient cycling and in the saprophytic survival of
many pathogens. Because of high C:N ratio of
litter as a consequence of plant growth under
elevated CO 2 , decomposition will be slower.
Increased plant biomass, slower decomposition
of litter, and higher winter temperature could
increase pathogen survival on overwintering crop