Effect of foliar application of ascorbic acid on sweet pepper (Capsicum annuum) plants under drought stress

Abstract

Drought is a harmful abiotic factor that clearly affects the growth and production of plants. The negative impacts of drought can be reduced by ascorbic acid (AsA) which is an important non-enzymatic antioxidant in plants. The purpose of the current investigation was to study the effects of different levels of drought and the external application of AsA on sweet pepper plants. The experiment had two factors, the first factor was drought: irrigation within the field capacity, moderate stress (irrigation within the 60% field capacity) and severe stress (irrigation within the 30% field capacity). The second factor was AsA: 0 mM sprayed with distilled water, 0.5 and 1 mM. The experiment had three replications. The results illustrated that drought stress reduced the fresh and dry weight of roots and shoots. It also reduced the relative water content (RWC), diameter and length of fruit, chlorophyll content and leaf area. Drought stress increased the activity of polyphenol oxidase and ascorbate peroxidase enzymes. It caused improvements in antioxidant properties, total phenolic content, ascorbate and electrical conductivity (EC) in the leaves of sweet pepper. Higher concentrations of AsA by foliar application significantly increased the values of all measured parameters except the EC. The interaction between ascorbic acid and drought stress showed that ascorbic acid significantly increased the shoot fresh weight, root dry weight, antioxidant properties, ascorbate, polyphenol oxidase and ascorbate peroxidase. However, it reduced the electrical conductivity. It is claimed that sweet pepper plants acquire tolerance to drought because AsA contributes to an increase in antioxidant properties.