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Maize is by quantity the most important C4 cereal crop; however, future climate changes are expected to increase maize susceptibility to mycotoxigenic fungal pathogens and reduce productivity. While rising atmospheric CO2 is a driving force behind the warmer temperatures and drought, which aggravate fungal disease and mycotoxin accumulation, our understanding of how elevated CO2 will effect maize defences against such pathogens is limited. Here we report that elevated CO2 increases maize susceptibility to Fusarium verticillioides proliferation, while mycotoxin levels are unaltered. Fumonisin production is not proportional to the increase in F. verticillioides biomass, and the amount of fumonisin produced per unit pathogen is reduced at elevated CO2 . Following F. verticillioides stalk inoculation, the accumulation of sugars, free fatty acids, lipoxygenase (LOX) transcripts, phytohormones and downstream phytoalexins is dampened in maize grown at elevated CO2 . The attenuation of maize 13-LOXs and jasmonic acid production correlates with reduced terpenoid phytoalexins and increased susceptibility. Furthermore, the attenuated induction of 9-LOXs, which have been suggested to stimulate mycotoxin biosynthesis, is consistent with reduced fumonisin per unit fungal biomass at elevated CO2 . Our findings suggest that elevated CO2 will compromise maize LOX-dependent signalling, which will influence the interactions between maize and mycotoxigenic fungi.
Vaughan et al. (Wed,) studied this question.