Elevating tolerance of drought stress in Ocimum basilicum using pollen grains extract; a natural biostimulant by regulation of plant performance and antioxidant defense system

Drought is a major abiotic stress that limits performance of sweet basil (Ocimum basilicum L.), which is an important aromatic plant for flavor foods and traditional medicines. The influence of palm pollen grains extract (PGE) on growth, physio-biochemical attributes, water use efficiency (WUE), anatomical characteristics and antioxidant defense system components in basil plants was investigated under normal and water deficit stress conditions. The PGE was exogenously applied as a foliar spray at a rate of 1.0 g L-1 to plants under full (70% of soil water-holding capacity; SWHC) or deficit irrigation (DI; 50% of SWHC) in a pot experiment repeated three times. Exposing basil plants to drought stress significantly disorganized their performance including oil yield and anatomical features, but increased their antioxidant defense system components. However, the application of PGE to DI-stressed plants significantly improved growth characteristics and the contents of essential oil, leaf photosynthetic pigments, soluble sugars, free proline, and ascorbic acid. Antioxidant enzyme activities, relative water content (RWC), WUE, and anatomical characteristics were also improved, while electrolyte leakage was significantly diminished compared to the corresponding control. Therefore, results obtained in this study recommend using PGE at 1.0 g L-1 as a foliar application strategy for Ocimum basilicum plants grown under DI stress to maintain higher RWC and WUE, and lower EL, and improve plant growth and essential oil productivity by limiting the inhibitory effects of DI. (C) 2019 SAAB. Published by Elsevier B.V. All rights reserved.