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Effect of Elevated CO2 on Phytoalexin Production in Soybeans
Braga, M.R., Aidar, M.P.M., Marabesi, M.A. and de Godoy, J.R.L. 2006. Effects of elevated CO2 on the phytoalexin production of two soybean cultivars differing in the resistance to stem canker disease. Environmental and Experimental Botany 58: 85-92.

What was done
The authors conducted three independent experiments where they grew well-watered soybean (Glycine max (L.) Merr) plants of two cultivars (IAC-14, susceptible to stem canker disease, and IAC-18, resistant to stem canker disease) from seed through the cotyledon stage in 5-liter pots placed within open-top chambers maintained at air CO2 concentrations of either 360 or 720 ppm in a glasshouse, while they measured various plant properties and processes, concentrating on the production of glyceollins (the major phytoalexins, or anti-microbial compounds, produced in soybeans) in response to the application of -glucan elicitor (derived from mycelial walls of Phythophthora sojae) to carefully created and replicated wounds in the surfaces of several soybean cotyledons.

What was learned
Whereas the IAC-14 cultivar did not exhibit a CO2-induced change in glyceollin production in response to elicitation, as Braga et al. hypothesized would be the case (since this cultivar is susceptible to stem canker disease), the IAC-18 cultivar (which has the potential to resist the disease to varying degrees) experienced a 100% CO2-induced increase in the amount of glyceollins produced after elicitation, a response the researchers described as remarkable.

What it means
In the words of Braga et al., the CO2-induced response they observed "may increase the potential of the soybean defense since infection at early stages of plant development, followed by a long incubation period before symptoms appear, is characteristic of the stem canker disease cycle caused by Dpm [Diaporthe phaseolorum (Cooke & Ellis) Sacc. f. sp. meridionalis Morgan-Jones]." Hence, they say this response "indicates that raised CO2 levels forecasted for next decades may have a real impact on the defensive chemistry of the cultivars."

Reviewed 6 December 2006