Effects of ozone and drought stress on growth, yield and physiology of tomatoes (Lycopersicon esculentum Mill. cv. Baladey)

An Egyptian cultivar of tomato (Lycopersicon esculentum Mill. cv. Baladey) was exposed to 68 nl l(-1) ozone (O-3) for 8 h d(-1) for 75 days in the ope n-top chambers at Braunschweig, Germany. Half of the plants were either ful ly irrigated or were subjected to a controlled drought stress treatment. O- 3 exposure caused visible injuries on the foliage of the tomato plants and decreased pigment content in the leaves. Drought stress alone had no effect on these parameters, but reduced the extent of foliar injury under O-3 str ess. Photosynthetic rate (A) and stomatal conductance (g(s)) of the plants were measured at regular intervals from the time when O-3 and drought stres s treatment were imposed. It was found that drought stress or O-3 alone cau sed a reduction in A by 21 and 17 %, respectively, while exposure to both s tresses resulted in the highest reduction in A. In contrast, O-3 caused a m ean increase in g(s) of 18 % in well-watered plants, while drought stress d ecreased g(s) by 22 %, compared to the well-watered control treatment. This stimulating effect of O-3 On g(s) was also seen in the combination with dr ought stress. Both O-3 and drought stress significantly suppressed biomass and fruit yield. Yield reductions by O-3 and drought stress alone were 48 a nd 29 %, respectively. How ever,suppression of yield was greatest in plants exposed to the combination of O-3 and drought stress. The results indicate d that 'Baladey' tomato is particular sensitive to O-3 exposures. It is sug gested that this sensitivity may even increase under water deficit conditio ns.