Paper Reviewed
Matić, S., Cucu, M.A., Garibaldi, A. and Gullino, M.L. 2018. Combined effect of CO2 and temperature on wheat powdery mildew development. The Plant Pathology Journal 34: 316-326.

Powdery mildew disease, caused by Blumeria graminis (Bgt), is a damaging foliar disease that affects worldwide wheat production, inducing estimated annual yield losses of 13 and 20% in winter and spring wheat, respectively (Griffey et al., 1993; Conner et al., 2003; Lackermann et al., 2011). Yet despite its negative impact on wheat production, little is known about how powdery mildew disease might respond to predicted changes in future climate and atmospheric CO2 concentrations.

Seeking to provide some relevant information in this regard, Matić et al. (2018) exposed wheat (Triticum aestivum, cv. Andino) plants at the flag leaf stage (ligule just visible) to three temperature (low: 18-22°C; medium: 22-26°C, high: 26-30°C) and two atmospheric CO2 concentration (450 or 850 ppm) combinations. Seven days after being transferred into these controlled-environment treatments, the plants were artificially inoculated with Bgt and the development of powdery mildew disease was monitored via a series of measurements ten days later.

So what did their experiment reveal?

Out of all the possible temperature and CO2 environments examined, the treatment showing "the most advantageous conditions for the progress of powdery mildew on wheat were low temperature and ambient CO2." In contrast, Matić et al. report that "elevated CO2 did not stimulate powdery mildew development" and "high temperatures inhibited pathogen growth independent of CO2 conditions."

Opining about the mechanism(s) behind the reduction in disease development at elevated CO2 and high temperature, Matić et al. write that "increased carbohydrate production might be associated [with] immunity of wheat plants [by] acting as elicitors of defense responses," including the regulation of pathogenesis-related genes. Alternatively, they state that "high temperatures probably inhibited spore germination which prevented disease development."

Regardless of the actual mechanism(s) inhibiting disease development, the results of this study suggest that if temperatures and/or the atmosphere's CO2 concentration rise in the future, the negative impacts of wheat powdery mildew disease on wheat production will be reduced. And that reduction will help to curtail the wheat production demands of the ever-growing global population.

References
Conner, R.L., Kuzyk, A.D. and Su, H. 2003. Impact of powdery mildew on the yield of soft white spring wheat cultivars. Canadian Journal of Plant Science 83: 725-728.

Griffey, C.A., Das, M.K. and Stromberg, E.L. 1993. Effectiveness of adult-plant resistance in reducing grain yield loss to powdery mildew in winter wheat. Plant Disease 77: 618-622.

Lackermann, K.V., Conley, S.P., Gaska, J.M., Martinka, M.J. and Esker, P.D. 2011. Effect of location, cultivar, and diseases on grain yield of soft red winter wheat in Wisconsin. Plant Disease 95: 1401-1406.