What was done
The authors grew well-watered and fertilized seedlings of a cultivar (Fitzroy) of the pencilflower (Stylosanthes scabra) - an important legume crop that is susceptible to anthracnose disease caused by Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. - within a controlled environment facility maintained at atmospheric CO2 concentrations of either 350 or 700 ppm, where they inoculated six-, nine- and twelve-week-old plants with conidia of C. gloeosporioides.  Then, ten days after inoculation, they counted the anthracnose lesions on the plants and classified them as either resistant or susceptible.

What was learned
Pangga et al. report that "the mean number of susceptible, resistant, and total lesions per leaf averaged over the three plant ages was significantly (P<0.05) greater at 350 ppm than at 700 ppm CO2, reflecting the development of a level of resistance in susceptible cv. Fitzroy at high CO2."  In fact, with respect to the plants inoculated at twelve weeks of age, they say that those grown "at 350 ppm had 60 and 75% more susceptible and resistant lesions per leaf, respectively, than those [grown] at 700 ppm CO2."

In terms of infection efficiency (IE), the team of Australian scientists say their work "clearly shows that at 350 ppm overall susceptibility of the canopy increases with increasing age because more young leaves are produced on secondary and tertiary branches of the more advanced plants."  However, they report that "at 700 ppm CO2, IE did not increase with increasing plant age despite the presence of many more young leaves in the enlarged canopy," which finding, in their words, "points to reduced pathogen efficiency or an induced partial resistance to anthracnose in Fitzroy at 700 ppm CO2."

What it means
As the air's CO2 content continues to rise, it would appear that the Fitzroy cultivar of the pasture legume Stylosanthes scabra will indeed acquire a greater intrinsic resistance to the devastating anthracnose disease.