Interaction of free air carbon dioxide enrichment (FACE) and controlled summer drought on fungal infections of maize

The recent report of the Intergovernmental Panel on Climate Change predicts an increase of atmospheric CO2 concentration, air temperature and summer drought conditions during the next decades. This will influence maize growth and also affect its susceptibility to fungal infection. Therefore, a two year experimental study was conducted, in which maize was grown in the field under ambient (ca. 380 ppm) and elevated atmospheric (550 ppm) CO2 concentrations and two watering regimes (well-watered or restricted water supply during summer). Moreover, in the second year all variants were combined with two mulching treatments (bare soil, straw mulch). In the first year, the rainy summer prevented the initiation of drought stress, which was assured in the second year by installation of rain shelters. Smut disease symptoms from Ustilago maydis were quite small and not influenced by the treatments. Infection by Exserohilum turcicum could be detected in the wellwatered treatments in the second year only. Leaf blight was slightly enhanced under elevated CO2 concentrations. Fusarium disease symptoms (ear rot, stem rot) could not be visually detected or were at a very low level and unrelated to the experimental treatments. However, the Fusarium mycotoxin deoxynivalenol (DON) indicating latent Fusarium infection was detected in whole plant samples and maize kernels. Under well-watered conditions no obvious influence on DON concentrations in whole maize samples was observed at elevated atmospheric CO2 (550 ppm), but DON in kernels was lower at 550 ppm than at 380 ppm atmospheric CO2 concentration. Under summer drought conditions, reduced DON levels were observed at 550 ppm CO2 and both mulching treatments compared to 380 ppm CO2 indicating a positive effect on the health status of maize at elevated atmospheric CO2 concentration when suffering from water deficit.