The interaction of O3 and CO2 concentration, exposure timing and duration on stem rust severity on winter wheat variety ‘Coker 9553’

Authors: MASHAHEET, ALSAYED - Damanhour University; Burkey, Kent; MARSHALL, DAVID - Retired ARS Employee

Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2023
Publication Date: 7/11/2023
Citation: Mashaheet, A., Burkey, K.O., Marshall, D. 2023. The interaction of O3 and CO2 concentration, exposure timing and duration on stem rust severity on winter wheat variety ‘Coker 9553’. Environmental Pollution. 334:122122. https://doi.org/10.1016/j.envpol.2023.122122.
DOI: https://doi.org/10.1016/j.envpol.2023.122122

Interpretive Summary: Our knowledge of the impacts of air pollution (ozone) and climate change on plant diseases is limited and at times conflicting due to the wide range of possible pathogen-environment interactions to be tested. A further challenge is the need for collaboration between diverse scientific disciplines. In this study, an international team of plant pathologists and plant physiologists from Egypt, North Carolina State University, and USDA-ARS at Raleigh, North Carolina grew wheat plants under combinations of elevated ozone and elevated carbon dioxide and then infected the plants with a stem rust pathogen. Ozone concentrations similar to present day air pollution levels increased stem rust disease severity relative to low ozone conditions. In contrast, elevated carbon dioxide concentrations predicted for later in the 21st century did not significantly impact disease. The results suggest that air pollution may impact wheat production by exacerbating stem rust disease in regions where ozone pollution and the pathogen coexist. This supports the need to continue the development of wheat varieties with greater disease resistance.

Technical Abstract: Wheat rusts, elevated ozone (O3), and carbon dioxide (CO2) are simultaneously impacting wheat production worldwide, but their interactions are not well understood. This study investigated whether near-ambient O3 is suppressive or conducive to stem rust (Sr) of wheat, considering the interactions with ambient and elevated CO2. Winter wheat variety ‘Coker 9553’ (Sr-susceptible; O3 sensitive) was inoculated with Sr (race QFCSC) following pre-treatment with four different concentrations of O3 (CF, 50, 70, and 90 ppbv) at ambient CO2 levels. Gas treatments were continued during the development of disease symptoms. Disease severity, measured as percent sporulation area (PSA), significantly increased relative to the CF control only under near-ambient O3 conditions (50 ppbv) in the absence of O3-induced foliar injury. Disease symptoms at higher O3 exposures (70 and 90 ppbv) were similar to or less than the CF control. When Coker 9553 was inoculated with Sr while exposed to CO2 (400; 570 ppmv) and O3 (CF; 50 ppbv) in four different combinations, and seven combinations of exposure timing and duration, PSA significantly increased only under continuous treatment with O3 for six weeks or pre-inoculation treatment for three weeks, suggesting that O3-predisposes wheat to the disease rather than enhancing disease post-inoculation. O3 singly and in combination with CO2 increased PSA on flag leaves of adult Coker 9553 plants while elevated CO2 alone had little effect on PSA. These findings show that sub-symptomatic O3 conditions are conducive to stem rust, contradicting the current consensus that biotrophic pathogens are suppressed by elevated O3. This suggests that sub-symptomatic O3 stress may enhance rust diseases in wheat-growing regions.