Variability in antioxidant and metabolite levels, growth and yield of two soybean varieties: An assessment of anticipated yield losses under projected elevation of ozone

Global mean tropospheric ozone concentration is expected to increase by more than 20% by 2050. Although the present levels of ozone may not induce visible symptoms in most of the plants, they can result in substantial production losses and reproductive output. There are wide variations in ozone sensitivity among varieties in same species. This paper reports variations in ozone sensitivity for two tropical soybean (Glycine max L.) varieties (PK 472 and Bragg) exposed to projected elevated ozone concentrations of 70 and 100 ppb for 4 h daily from germination to maturity under natural field conditions. Differential sensitivities of cultivars to ozone were assessed by comparing the levels of antioxidative potential, metabolite production, growth behaviour, biomass accumulation and yield responses. The activity of catalase decreased whereas peroxidase increased in both the varieties upon exposure to O3, however, the magnitude of change was always higher in PK 472 as compared to Bragg. The larger magnitude of reductions in the levels of antioxidants, metabolites and nutrients also reflected the greater sensitivity of PK 472 compared to Bragg. The differential response of biochemical characteristics corresponded to significant reductions in plant length, number and area of leaves, component-wise biomass and yield parameters of PK 472 as compared to Bragg. This work emphasizes the greater sensitivity of a newly developed variety PK 472 of soybean compared to that of the older variety, Bragg. Further, the effects of ozone on different plant characteristics were found to be more prominent during reproductive than vegetative growth in these two varieties. In view of the anticipated increasing tropospheric O3 concentrations the in near future, the results of the present study can be utilized in screening out more resistant varieties of soybean for greater agricultural productivity.