Differences in responses of two mustard cultivars to ethylenediurea (EDU) at high ambient ozone concentrations in India

• Mustard (Brassica campestris) cultivars were sensitive to ambient ozone levels.
• EDU-induced response in mustard cultivars differed.
• Antioxidants play a key role in EDU action in B. campestris
• Mustard yield and seed oil content increased with EDU treatment.

Ethylenediurea (EDU) at two different concentrations (200 ppm and 400 ppm) was used as a tool to study the response of two local Indian cultivars (Kranti and Peela sona) of mustard (Brassica rapa syn. B. campestris) to ambient ozone conditions. During the experiment, the critical AOT 40 levels were exceeded in the area of study in the Indo-Gangetic plains. Seed weight, biomass, oil content of the seeds and chlorophyll content increased at both EDU treatment levels in both cultivars. Gas exchange parameters (stomatal conductance and photosynthesis) were not affected by the EDU treatment, while the responses of antioxidative enzymes varied between the cultivars. The results indicate that EDU-induced ozone protection in these mustard cultivars is mediated by an antioxidative defense system, and that the cultivars adopted different strategies against ozone stress. The cultivar Kranti, characterized by higher biomass accumulation and number of pods, showed stronger antioxidative defense through several enzymes throughout the experiment, whereas the cultivar Peela sona, characterized by earlier senescence and a greater resource allocation to seed weight, invested in enzymatic detoxification only during the vegetative phase. The seed oil content increased by 4–5% at higher EDU treatment in both cultivars, which causes concern for mustard oil production at current ozone levels in India. Obviously, wider screening, using controlled ozone treatments, of B. campestris cultivars is urgently needed in order to maintain and improve the production rates in this highly populated and polluted area of India.