Field Interactions Between Ozone and Naturally Occurring Fungal Disease in Maize Inbreds.

The rise in tropospheric ozone (O₃) associated with climate change is already reducing potential maize (Zea mays L.) yields. Interactions with other abiotic and biotic stresses can further complicate field management under future conditions. Free Air Enrichment Facilities (FACE) provide tools for studying the field effects of ozone and disease interactions. A diverse panel of maize inbred lines, including the founders of the nested association mapping (NAM) population, was grown under ambient (40 ppb) and elevated (100 ppb) ozone concentrations at the SoyFACE facility at Champaign, IL, during the 2013, 2014 and 2015 seasons and naturally occurring disease (foliar, ear and stalk rots) was evaluated. The most commonly observed foliar diseases were Common rust (Puccinia sorghi; biotroph), Northern leaf blight (Exserohilum turcicum; hemibiotroph), Gray leaf spot (Cercospora zeae-maydis; necrotroph) and Brown spot (Physoderma maydis; biotroph).Foliar disease and fungal ear rot were evaluated on a severity scale, 9 and 6 points respectively, at different time points in the season. Stem rot was evaluated as presence/absence at the end of the season. Within seasons disease severity was highly genotype-dependent; however there were ozone effects, most significant under high-disease pressure seasons. Brown spot shows lower severity under elevated ozone; while Northern corn leaf blight and stem rots show higher severity under elevated ozone later in the season. Ozone appears to affect disease severity on a physiological level, influenced by the pathogen’s lifestyle, and on a cellular level through a potential pathosystem-specific priming of defense responses.