Background
The authors state that "potato late blight caused by the oomycete Phytophthora infestans (Mont.) de Bary is the most devastating disease of potato worldwide," and that "infection occurs through leaves and tubers followed by a rapid spread of the pathogen finally causing destructive necrosis."

What was done
Plessl et al. grew individual well watered and fertilized plants of the potato cultivar Indira in 3.5-liter pots filled with a 1:2 mixture of soil and "Fruhstorfer T-Erde" in controlled-environment chambers maintained at atmospheric CO2 concentrations of either 400 or 700 ppm. Four weeks after the start of the experiment, the first three fully-developed pinnate leaves were cut from the plants and inoculated with zoospores of P. infestans in Petri dishes containing water-agar, after which their symptoms were evaluated daily via comparison with control leaves that were similarly treated but unexposed to the pathogen.

What was learned
The German researchers report that the 400 to 700 ppm increase in CO2 "dramatically reduced symptom development," including extent of necrosis (down by 44% four days after inoculation and 65% five days after inoculation), area of sporulation (down by 100% four days after inoculation and 61% five days after inoculation), and sporulation intensity (down by 73% four days after inoculation and 17% five days after inoculation).

What it means
Plessl et al. say their results "clearly demonstrated that the potato cultivar Indira, which under normal conditions shows a high susceptibility to P. infestans, develops resistance against this pathogen after exposure to 700 ppm CO2," noting that "this finding agrees with results from Ywa et al. (1995), who reported an increased tolerance of tomato plants to Phytophthora root rot when grown at elevated CO2." These similar observations bode well for both potato and tomato cultivation in a CO2-enriched world of the future.

Reference
Ywa, N.S., Walling, L. and McCool, P.M. 1995. Influence of elevated CO2 on disease development and induction of PR proteins in tomato roots by Phytophthora parasitica. Plant Physiololgy 85 (Supplement): 1139.