Response of the Rieger begonia to ozone and sulphur dioxide

Ozone (O₃) and sulphur dioxide (SO₂) are at present the two most pervasive air pollutants in the urban and suburban areas in which most Rieger begonias are grown. These air pollutants have been shown to impair crop productivity and quality in many other species. Controlled environment experiments were therefore conducted to elucidate the responses of ‘Schwabenland Red’ to separate or bombined O₃ and SO₂ at different growth stages.Plants at the early vegetative or prefloral stages had much more leaf damage after combined O₃ + SO₂ than after separate gases at 15 p.p.h.m. O₃ or 60 p.p.h.m. SO₂ for 5 days in a synergistic type of response. Exposure for an additional day at twice these concentrations greatly increased leaf damage. Growth reductions were not found after 2 weeks but delaying measurements until 8 weeks after treatment revealed some growth reductions.Experiments were conducted with flowering plants using O₃ of 0, 10, 20 or 30 p.p.h.m. in all combinations with SO₂ at 0, 60, 120 or 180 p.p.h.m. Fully developed leaves were damaged, and undamaged leaves were smaller and lighter on plants exposed to 20 p.p.h.m. or more O₃, 120 p.p.h.m. or more SO₂, or any combination of O₃ and SO₂ at or above 10 and 60 p.p.h.m., respectively.