Global Climate Change and Implications for Future Plant Disease Epidemics
Department of Crop Sciences
Human activities have altered the earth’s atmospheric composition, increasing levels of both carbon dioxide and ozone. Levels of these two gasses are predicted to continue to climb well into the 21st century. By the year 2050, carbon dioxide is expected to reach levels double those of the preindustrial era, and ozone levels are increasing by as much as 2.5% a year. Plant diseases are the result of interactions between susceptible host plants, virulent pathogens, and favorable environments. So it is logical to presume that changes in the climate will have an effect on the types and severity of plant diseases, including those on agricultural crops.
Over the past decade, climate change experiments have been used to look at the impact of elevated carbon dioxide levels (CO2 ), ozone (O3) levels, and atmospheric temperatures on crop growth and performance, and, to some extent, to evaluate the effect that changing climate conditions will have on the development of plant diseases. These studies have shown that some plant disease epidemics are likely to be more severe, some less severe, and some diseases will not be greatly impacted by the predicted changes.
While elevated CO2 levels might have a direct effect on plant pathogens, they are most likely to have an impact on plant diseases by the changes they cause in the plant hosts. Plants growing in a high CO2 environment tend to grow faster and larger, and they have denser canopies. These dense plant canopies favor the development of some diseases because the low light levels and reduced air circulation allow higher relative humidity levels to develop, and this promotes the grown and sporulation of many plant pathogens. However, plants grown in high CO2 environments also close their stomata more of the time. Stomata are the pores in the leaves that allow the plant to take in CO2 and give off oxygen. Some plant pathogens enter the plant through the stomata, and if the stomata are not open, the pathogen has a more difficult time getting into the plant. Plants grown in high ozone environments tend to be shorter, with less dense canopies, which slows the development of some diseases because the more open, less humid canopy slows the growth and reproduction of certain pathogens. However, O3 also damages plant tissues, which helps some pathogens to infect the plant. So both elevated levels of CO2 and O3 can make a plant more susceptible to some diseases, but less susceptible to others, and this is exactly what has been observed in climate change experiments.
Rising temperatures and changes in rainfall patterns will also have an impact on the development on plant disease epidemics. In some cases, changes of a only a few degrees have allowed plant diseases to become established earlier in the season, resulting in more severe disease epidemics, and the ranges of some diseases are expanding as rising temperatures are allowing pathogens to overwinter in regions that previously had been too cold for them. For example, warmer winter temperatures may allow Kudzu to expand its range northward. Because Kudzu is an alternate host for the soybean rust pathogen, one result of rising temperatures may be that soybean rust arrives in Illinois earlier in the soybean growing season.
The information derived from climate change studies will help us prepare for the changes to come by knowing which diseases are most likely to become more problematic. This knowledge will allow plant pathologists, plant breeders, agronomists, and horticulturalists to adapt disease management strategies to the changing environment.