Paper Reviewed Zou, Z., Liu, F., Chen, C. and Fernando, W.G.D. 2019. Effect of elevated CO2 concentration on the disease severity of compatible and incompatible interactions of Brassica napus-Leptosphaeria maculans pathosystem. Plants 8: 484, doi:10.3390/plants8110484. Writing as background for their study, Zoe et al. (2019) note that “plant disease symptoms in pathosystems are influenced by, or require, three components-a susceptible host, an aggressive or virulent pathogen, and a conducive environment for the pathogen to cause disease,” while adding that “variations in environmental conditions, including CO2 concentration change, may potentially affect plant disease susceptibility and severity.” And thus they go on to explain how they explored the relationship between canola (Brassica napus) and blackleg (a fungal pathogen caused by Leptosphaeria maculans) under normal (400 ppm) or elevated (800 ppm) CO2 concentrations. The work was conducted in a controlled-environment using canola varieties and lines with differing levels of resistance to blackleg disease, as well as various blackleg isolates of differing gene profiles. Results of the study revealed that elevated CO2 had “no noticeable effect on the inferred phenotypes of the canola-blackleg interactions.” However, Zou et al. report that “disease severity decreased in most of the B. napus-L. maculans interactions at extremely high CO2 concentration (800 ppm).” In searching for an explanation of this important finding, the authors write that “the effects of elevated CO2 concentration on physiological processes, leaf chemistry, the stomatal opening system, and even on L. maculans growth rate, sporulation and aggressiveness, probably caused the decreased disease severity of canola seedlings inoculated by different L. maculans isolates,” albeit they recognize that “further studies are needed to investigate causes of the inhibition of Leptosphaeria isolates’ pathogenicity on the canola plant under elevated CO2 concentration and at the molecular level. But in the meantime, we can pause and celebrate the good news of their generalized findings that blackleg disease severity was reduced under elevated CO2!   This article appeared on the CO2 Science website at http://www.co2science.org/articles/V23/apr/a3.php]]>