Development of lines of radish differing in resistance to O 3 and SO 2

SUMMARY The potential for developing intraspecific lines of radish ( Raphanus sativus L. cv, Cherry Belle) based on their relative resistance to either O 3 or SO 2 was examined using growth‐analysis techniques. Plants were exposed to either 0–10μ 1 −1 O 3 or 0.50 μ 1 −1 SO 2 for 4 h day −1 , 3 days week −1 , for 3 weeks. Resistant and sensitive individuals were then selected and divided into four groups: O 3 resistant ( O 3 R ), O 3 sensitive (O 3 S), SO 2 resistant ( SO 2 R ), and SO 2 sensitive ( SO 2 S ) Cross‐pollinations were made among plants within the selected groups and seed collected. F 1 populations were raised from the resulting seed and exposed to the same exposure regime. Net photosynthesis and stomatal conductance were measured during the final two fumigations, and plants were harvested immediately following the final exposure, divided into component parts, dried and weighed. O 3 and SO 2 generally caused biomass reductions in all the F 1 groups. O 3 reduced below ground growth more than SO 2 leading to greater reductions in root/shoot ratios. O 3 R plants were resistant to both pollutants, showing little biomass reduction particularly from O 3 . Root/shoot ratios of these plants were altered less by pollutant exposure than non‐selected radishes. Shoot growth of SO 2 R plants was greater in O 3 or SO 2 than non‐selected plants, but below ground growth was similar. Selection for plants sensitive to either pollutant was not apparent from growth analysis, as growth of the sensitive plants was generally the same as that of non‐selected plants. Gas exchange results indicated greater stomatal conductance in O 3 S plants in filtered air than either non‐selected or O 3 R plants, while O 3 S plants had lower conductance rates in the O 3 treatment.