Application of Humic Acid and Algal Extract: An Eco-friendly Strategy for Improving Growth and Essential Oil Composition of Two Basil Varieties under Salty Soil Stress Conditions

Abiotic stress factors such as salinity, drought, flooding, as well as low and high temperatures are the main factors that drastically influence crop yield worldwide. The current study was designed to evaluate the effects of foliar spraying with humic acid and algal extract alone or in combination with organic fertilizers under salty soil conditions on the growth, essential oil composition, and quality of two basil varieties (O. basilicum var. basilicum and O. basilicum var. Genovese). Growth characters significantly increased when plants were sprayed with 1.5% humic acid and/or 3 ml/L algal extract (oligo X) as control < humic acid < algal extract (oligo X) < humic acid + algal extract (oligo X). Also, essential oil composition, yield, and proline content significantly increased after spraying with humic acid 1.5% and/or 3 mL/L algal extract. The two varieties differed in their growth characteristics; the number of branches and herb fresh weight; as well as essential oil percentage and yield per plant under control conditions, and thus differences were due to the differences in salinity stress tolerance. Both varieties differed in their response to treatments with humic acid and algal extract. The GC/MS results show the presence of 30 components in the essential oils of the studied basil plants. The major compounds were linalool, Estragole, and Eucalyptol. Linalool and Eucalyptol were much higher in O. basilicum L., while Estragole was much higher in O. basilicum var. Genovese. These results revealed humic acid and algal extract's vital role as eco-friendly fertilizers in improving basil plant growth, yield, and quality under salinity stress conditions. Which may be involved in sustainable medicinal plant production.