The Effect of CO2 and O3 Levels on Soybean Diseases

This experiment analyzed the effects that a change in the atmospheric composition will have on the diseases that infect soybean<!–[if supportFields]> XE “soybeans” <![endif]–><!–[if supportFields]><![endif]–> crops. Specifically, Eastburn et al. (2010) researched the implications associated with an increase in CO2 and O3<!–[if supportFields]> XE “ozone, O3″ <![endif]–><!–[if supportFields]><![endif]–> levels, comparing these results to ambient conditions. The three soybean diseases observed were brown<!–[if supportFields]> XE “brown” <![endif]–><!–[if supportFields]><![endif]–> spot, downy mildew, and sudden death syndrome (SDS). The results showed that, throughout the span of the study, both an increase in CO2 and a combined increase in CO2 and O3 are expected to cause a decrease in downy mildew severity but an increase in brown spot severity. However, the different atmospheric conditions did not have a significant effect on either the brown spot or the sudden death syndrome incidence. The data also showed that higher levels of precipitation lead to greater downy mildew severity. Generally speaking, warmer conditions exacerbated both brown spot and downy mildew severity, but chemical analysis showed no change in the structural and chemical composition of the soybean.—Daniela Hernandez
 Eastburn, D., Degennaro, M., Delucia, E., Dermody, O., McElrone, A., 2010. Elevated atmospheric carbon dioxide and ozone<!–[if supportFields]> XE “ozone, O3″ <![endif]–><!–[if supportFields]><![endif]–> alter soybean<!–[if supportFields]> XE “soybeans” <![endif]–><!–[if supportFields]><![endif]–> diseases at SoyFACE. Global Change Biology 16, 320–330.

Eastburn et al. conducted the present study throughout a three-year time span from 2005 to 2007. The researchers did not want to discount the effects that certain climatic parameters might have on the soybean<!–[if supportFields]> XE “soybeans” <![endif]–><!–[if supportFields]><![endif]–> diseases. Instead of growing soybeans under controlled conditions, they, therefore, used the soybean free air concentration enrichment facility, SoyFACE, located on the University of Illinois campus, in which conditions such as temperature and precipitation could occur naturally. The four atmospheric composition conditions tested in the present study were: ambient conditions, elevated CO2, elevated O3<!–[if supportFields]> XE “ozone, O3″ <![endif]–><!–[if supportFields]><![endif]–>, and a combination of elevated CO2 and O3 levels. Conditions were measured regularly to calculate the adequate level of CO2 and O3 that the plants needed to be exposed to.
The authors conducted random samplings of the soybean<!–[if supportFields]> XE “soybeans” <![endif]–><!–[if supportFields]><![endif]–> plants in the varying plots. They tested leaves of those plants showing signs of infection to see whether the diseases (brown<!–[if supportFields]> XE “brown” <![endif]–><!–[if supportFields]><![endif]–> spot, downy mildew, and sudden death syndrome) were the actual cause of the symptoms. Brown spot disease affects plants by causing brown spots bounded by chlorotic tissue on the leaves. The symptoms of downy mildew show up as spots on the top surface of leaves and lesions on the bottom surface. Although sudden death syndrome is actually a root disease, the leaves also show spots when infected.
To quantify the effect of atmospheric changes on the soybean<!–[if supportFields]> XE “soybeans” <![endif]–><!–[if supportFields]><![endif]–> diseases, both disease incidence and severity were measured through visual inspection and a digital image analysis (ASSESS: Image analysis software for plant disease quantification), respectively. Disease incidence was measured as the positive or negative infection of the plant and number of lesions, calculated as a percentage. Severity, however, was quantified by measuring the proportion of the leaf area that was infected as well as the individual lesion size, again calculated as a percentage. Because they are a way of understanding plant defense, cuticle wax as well as carbon and nitrogen<!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–> content were measured from the leaf tissue using a chemical analysis. These values offered a further insight as to the impact the diseases had on the soybean.

Soybean is an economically and practically significant crop; its use ranges from food products to the production of biodiesel<!–[if supportFields]> XE “biodiesel” <![endif]–><!–[if supportFields]><![endif]–>. Therefore, it is crucial that research be done to expand on current knowledge of the effect of climatic and atmospheric change on the crop and to implement future management strategies.

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