Leaf traits that contribute to differential ozone response in ozone-tolerant and sensitive soybean genotypes

Authors: Bailey, Amanda; Burkey, Kent; TAGGART, MATTHEW - North Carolina State University; RUFTY, THOMAS - North Carolina State University

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2019
Publication Date: 7/20/2019
Citation: Bailey, A.R., Burkey, K.O., Taggart, M., Rufty, T. 2019. Leaf traits that contribute to differential ozone response in ozone-tolerant and sensitive soybean genotypes. Plants. 8:235.

Interpretive Summary: Ground level ozone is formed by the action of sunlight on volatile hydrocarbons and nitrogen oxides produced during combustion of carbon based fuels. Although frequently considered an urban problem, ozone pollution is much broader in scope because weather systems transport the pollutants into agricultural areas. Ozone is toxic to plants, causing visible injury to foliage and a reduction in the growth and yield of sensitive crops such as soybean. Estimates suggest that current ambient ozone levels are sufficient to reduce soybean yield by 10% or more with greater yield losses anticipated if tropospheric ozone concentrations continue to rise. In the absence of international efforts to control air pollution, future soybean productivity may depend on the development of ozone-tolerant varieties. A first step in developing improved cultivars is identification of traits that can be used as selection criteria in plant breeding programs. In this study, a team of researchers from the USDA-ARS Plant Science Research Unit and North Carolina State University in Raleigh, North Carolina identified ozone exclusion as a trait in ozone-tolerant Fiskeby III soybeans that reduces ozone damage by limiting ozone uptake into leaves while maintaining high rates of photosynthesis. This finding is being used by breeders in the USDA-ARS Soybean and Nitrogen Fixation Unit in Raleigh, North Carolina to develop soybeans with greater tolerances to both ozone and drought stress.

Technical Abstract: Ozone (O3) is a phytotoxic air pollutant that limits crop productivity. Breeding efforts to improve yield under elevated O3 conditions will benefit from understanding the mechanisms that contribute to O3 tolerance. In this study, leaf gas exchange and antioxidant metabolites were compared in soybean genotypes [Glycine max (L.) Merr] differing in ozone sensitivity. Mandarin (Ottawa) (O3-sensitive) and Fiskeby III (O3-tolerant) plants grown under charcoal-filtered air (CF) conditions for three weeks were exposed for five days to either CF conditions or 70 ppb O3 in Continuously Stirred Tank Reactors (CSTRs) in a greenhouse. In the CF controls, stomatal conductance was approximately 36% lower for Fiskeby III relative to Mandarin (Ottawa) while the two genotypes exhibited similar levels of photosynthesis. Ozone exposure induced significant foliar injury on leaves of Mandarin (Ottawa) associated with declines in both stomatal conductance (by 77%) and photosynthesis (by 38%). In contrast, O3 exposure resulted in minimal foliar injury on leaves of Fiskeby III with only a small decline in photosynthesis (by 5%), and a further decline in stomatal conductance (by 30%). There was a general trend towards higher ascorbic acid content in leaves of Fiskeby III than in Mandarin (Ottawa) regardless of treatment. The results confirm Fiskeby III to be an O3-tolerant genotype and suggest that reduced stomatal conductance contributes to the observed O3-tolerance through limiting O3 uptake by the plant. Reduced stomatal conductance was associated with enhanced water use efficiency, providing a potential link between O3 tolerance and drought tolerance.