Mitigating the Atmospheric Pollutant Injuries on Pear Trees Grown near the Freeways Via Application of Various Anti-Stress Compounds to Ameliorate Fruit Quality and Storability

Abstract

Crop plants could be dramatically injured by exposing to air pollutants. Despite the damage symptoms can be visualized on tree foliage during growth cycles in the field, the possible extend effects of pollutants on fruits quality are not obviously investigated. Thus, the current work aimed to outstanding the after harvesting changes in pear fruit obtained from air pollutants-stressed-trees. The exogenous applications efficacy of salicylic acid (SA), ascorbic acid (AA), proline (Pro), and sodium hydrosulfide (NaHS were applied on 12 year-old ‘Le Conte’ pear trees for alleviating air pollutants stress. The treatments of SA (200 and 400 mg/l), AA (1000 and 2000 mg/l), Pro (100 and 200 mg/l), and NaHS (250 and 500 µM) were applied on trees grown on 10 and 50m distances of the freeway. The harvested pear fruits were stored at 4 ± 1⁰C and 80–85% RH. Fruit firmness, vitamin C, acidity, total phenols, and total antioxidants were decreased during storage, while fruit weight loss, total soluble solids (TSS), TSS/acidity, total sugars, and superoxide dismutase were increased. Fruit from trees planted at 10m had higher firmness, acidity, total phenols, antioxidants, peroxidase, and superoxide dismutase. However, vitamin C, TSS, TSS/acid, and total sugars were lower than those taken from trees planted at 50m of the freeway. SA, AA, Pro, and NaHS treatments decreased fruit weight loss. In addition, the treated fruit had higher firmness, vitamin C, TSS, TSS/acid, total sugars, total phenols, total antioxidants, and peroxidase and superoxide dismutase activities. Fruit treated with AA (2000 mg/l) had the highest concentration of vitamin C compared with the rest of the treatments. The most phenols increments resulted from AA and NaHS treatments. Moreover, fruit treated with SA had the highest content of antioxidants followed by fruit treated with AA and NaHS. The AA and NaHS treatments significantly increased peroxidase activity and superoxide dismutase over the control. The presence of pear trees located 10m away from the freeway resulted in an unfavorable environment for the fruit to ripen. The fruit located 50m away from the freeway ripened faster and earlier than at 10m. It could be concluded that SA, AA, Pro, and NaHS reduced the impact of air pollution on the yield and quality of ‘Le Conte’ pear grown adjacent to the freeway. Since such chemical compounds increased the fruit’s tolerance to air pollutants stress, it is advisable to be applied as pre-harvest agronomic practice in pear trees grown near the highways.