**2. Materials and Methods**

This study was conducted during the 2021/2022 growing season at the Department of Pomology, Faculty of Agriculture, Cairo University, Egypt. All chemicals used in this study were reagent-grade and purchased from many worldwide suppliers (Bio Basic Inc., Markham, ON, Canada; Caisson Laboratories Inc., North Logan, UT, USA; Chem-Lab, Zedelgem, Belgium; Loba Chemie Pvt. Ltd., Maharashtra, India; Merck Ltd., Darmstadt, Germany; SDFCL, Chennai, India, and Sigma-Aldrich, Taufkirchen, Germany). Unless otherwise specified, all solutions were prepared in distilled water.

#### *2.1. Greenhouse, Chilling Chamber Preparation, and Plant Materials*

One-year-old mango (*Mangifera indica* L., cv. "Seddik") transplants grafted on "Sukkary" rootstock were used. The selected plants had uniform sizes, received the recommended water amounts to prevent the development of water deficit, were supplemented with macro- and microelements, and were treated with suitable pesticides to prevent other biotic stresses. A greenhouse was prepared for mango transplants' growth and recovery under normal growth conditions (25 ◦C/20 ◦C, day/night) before and after exposure to chilling. A chilling room was prepared to expose the mango transplants to chilling stress at 4 ± 1 ◦C. This temperature was determined based on the last decade's data (Figure 1) provided by the Central Laboratory for Agricultural Climate (CLAC).

**Figure 1.** Minimum mean January, February, and March temperatures (open-air temperature) during the last decade in Giza district, Egypt.

#### *2.2. Exogenous Salicylic Acid Treatments and Chilling Stress Induction*

Salicylic acid (SA) was sprayed 48 and 24 h before the chilling treatment for 3 d at different concentrations (0, 0.5, 1, and 1.5 mM) on uniform juvenile mango transplants of "Seddik" cultivar. SA was dissolved in a NaOH solution (0.002 N); the pH was adjusted to 6.8 before the treatment. Then, Tween 80 was added at 0.1% as a surfactant. Untreated (treated with tap water) transplants exposed to chilling represented the positive control, while untreated transplants not exposed to chilling and kept under greenhouse conditions (25 ◦C/20 ◦C, day/night) throughout the entire period were the negative control.

For chilling exposure, the transplants were transferred to the Agriculture Development Systems (ADS) project's growth chamber, Faculty of Agriculture, Cairo University, at 4 ± 1 ◦C for 72 consecutive hours, followed by a period of six days of recovery under greenhouse conditions (25 ◦C/20 ◦C, day/night).
