Plant pathogens and the diseases they cause are estimated to cause a 10 – 16% decrease in crop yield worldwide, with an additional 6 – 12% loss attributed to postharvest spoilage. However, changes in the global climate as a consequence of rising atmospheric carbon-dioxide (CO2) are expected to further impact these losses. Crown rot (CR) of wheat has provided an excellent model to study the effects of elevated CO2 (eCO2) on disease incidence, severity, pathogen colonisation and the subsequent effect on grain yield. The effect of eCO2 on the CR pathogen, Fusarium pseudograminearum was assessed in controlled environment facilities (CEF), glasshouse experiments and at the Australian Grains Free-Air CO2 Enrichment (AGFACE) field experiment near Horsham, Victoria. The influence of CO2 on crown rot development was shown to be dependent on a number of factors: 1) The CO2 effect on CR was dependent on temperature or growing season. 2) CR incidence and susceptibility on average increased under eCO2, and the CO2 effect was dependent on the genotype; 3) When CR severity was correlated with pathogen colonisation, CR severity was higher per unit of infected host tissue under elevated CO2; 4) Yield penalty at eCO2, due to CR, was greater in wheat grown under eCO2. 5) CR incidence, severity and pathogen colonisation were also dependent on the host growth stages and temperature.
Our findings show that an increase in atmospheric CO2 has the potential to increase disease incidence and severity by influencing host susceptibility while causing a reduction in the potential grain yield. These studies, therefore, show CR is likely to become more problematic for farmers unless effort is made to integrate wheat genotypes with durable CR resistance under eCO2 into breeding programs.