الفهرس 
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Abstract
The harmful impacts of ozone (O3) on plant development and productivity have been excessively studied. Furthermore, the positive influences of its low concentrations still need to be explored further. The experiments were conducted at the International Protected Cultivation Farm, Faculty of Agriculture, Kafrelsheikh University, Egypt, during the winter seasons of 2016/2017 and 2017/2018 on two sweet pepper hybrids (Lirica and Zidenka) under an unheated plastic-house. The main objective of this work was to study the effects of a group of exogenous ozone (O3) concentrations (0, 1, 5, 10, 20, 30 and 60 ppm), as well as, chilling treatment to induce chilling tolerance compared to untreated control on some germination parameters, transplant quality, vegetative growth, fruit yield, fruit quality and chemical constituents.
Four O3 concentrations (0, 1, 5, 10 and 20 ppm) were applied in the first season. However, the lower concentrations (1 and 5 ppm) were cancelled and replaced by two higher concentrations (30 and 60 ppm), in the second season. O3 concentrations were compered to chilling treatment (4±1 °C for 36 h at light) and untreated control. These treatments were performed in two separate experiments. The first one was conducted as seed soaking and the second as seedlings spry.
Ozone treatment significantly improved germination parameters, transplant quality, vegetative growth (plant height, number of leaves/plant and leaf area/plant), fruit yield (early, total and marketable), fruit quality (length, diameter, ascorbic acid, and TSS) and leaf chemical constituents. Moreover, ozone treatment promoted transplant and plant maintenance of high relative water content, chlorophyll, proline and ascorbate peroxidase activity under cold stress conditions. Ozone also protected the cell wall from damage as it decreased cell membrane permeability. Generally, the best results were obtained from 30 ppm O3 as seed soaking or transplant spray. In most cases, chilling acclimation treatment had intermediate values between the control and ozone treatment. The results pointed out the possible use of ozone in low concentrations to protect the plants from cold stress during sweet pepper production under unheated plastic-house.