Effect of elevated CO2 on maize susceptibility to grey leaf spot disease

Abstract

Atmospheric CO2 concentrations have been rising considerably over the last century and are forecast to reach 800-1000 ppm by 2100. Maize is an important C4 crop that is cultivated around the world; however, its production is subjugated to yield losses due to Cercospora zeina-induced grey leaf spot (GLS) disease. The aim of this study was to investigate the effect of elevated [CO2] on maize susceptibility to GLS across two growing seasons. Maize plants were grown at 415 and 700 ppm CO2 in enclosed growth chambers and there was no difference in plant height-based growth rates of the B73 maize between CO2 regimes in either trial. Gas exchange parameters were assessed, and increased leaf photosynthetic rates were observed for maize grown at elevated CO2 levels in both trials, while greater stomatal conductance was measured on the high CO2-grown plants in the second trial only. Maize leaf stomatal density and in vitro C. zeina growth were shown to be unaffected by elevated [CO2], along with maize leaf sugars, such as glucose and sucrose. However, maltose concentrations were significantly greater at 415 ppm than 700 ppm CO2. Maize leaves were inoculated with C. zeina, and disease development was recorded and quantified, wherein no CO2 effect was documented in the first trial. Significantly greater GLS symptoms were observed on plants grown at elevated [CO2] than ambient in the repeat trial, although this was a consequence of limited GLS development in the ambient CO2-grown maize. Analysis of the environmental data from each chamber suggests that a chamber effect occurred in the second trial due to relatively lowered humidity in the ambient CO2 chamber during the critical period for C. zeina infection following inoculation. Therefore, the conclusion is that maize susceptibility to GLS will not be significantly affected by elevated [CO2], which demonstrates a neutral effect of climate change on one major maize disease.