Background
The authors write that "Eucalyptus wilt, which is caused by Ceratocystis fimbriata Ellis and Halst, is one of the main diseases of this [tree] crop and widely distributed throughout the world." They additionally indicate that C. fimbriata "is a typical xylem pathogen and requires the presence of wounds for penetration," noting that "such wounds can be caused by vector insects, wind, hail and management practices," citing Baker and Harrington (2004).

What was done
Clonal plantlets of two Eucalyptus hybrids were studied in twice-replicated experiments conducted in a climate-controlled room (27±2°C, 40% relative humidity, photoperiod of 12 hours) at three different atmospheric CO2 concentrations (394, 553 and 878 ppm), where after 70 days aliquots of 100 µL of C. fimbriata conidia suspension were injected into the plants' wounds, which were afterwards covered with Parafilm.

What was learned
Compared to the 394-ppm CO2 treatment, the plantlets of both clones grown in the 553 and 878 ppm CO2 treatments had, in the words of the four researchers, "greater growth (215% and 219% increases in leaf area and 22% and 24% in stem diameter, respectively," as well as "less disease severity (48% and 78% reduction, respectively) on average compared with the plants cultivated at 394 ppm."

What it means
In the concluding sentence of their paper's abstract, dos Santos et al. say their results show that "an increased CO2 concentration can reduce the severity of Ceratocystis wilt and stimulate the growth of Eucalyptus clonal plantlets." And it does it all ... at one and the same time.

Reference
Baker, C.J. and Harrington, T.C. 2004. Ceratocystis fimbriata. CABI Publishing, Wallingford, Oxfordshire, UK.