The Beneficial Role of Salicylic Acid, Triacontanol and δ-Aminolevulinic Acid on the Growth, Flowering and Chemical Composition of Pansy (Viola wittrockiana Gams) under Salt Stress Conditions

Two pot trials were carried out during the two successive Winter seasons of 2015/2016 and 2016/2017 at private commercial nursery, Damanhour city, El-Beheira Governorate, Egypt under greenhouse conditions. The objective of these experiments was to study the effect of foliar application with each of salicylic acid (SA) (50 and 100 mgL^-1), triacontanol (TRIA) (25 and 50 mgL^-1) and δ-aminolevulinic acid (ALA) (25 and 50 mgL^-1) on Viola wittrockiana Gams L. (Blue with Blotch cultivar) grown under different concentrations of salinity (0, 20, 40 and 60 mM of NaCl). Generally, the tested materials were varied in their significant effects on studying characters. The obtained results of the two seasons indicated that increasing salinity levels from 20 to 60 mM significantly reduced all studied parameter levels, i.e., plant height, branches number per plant, shoot dry weight per plant, leaf area, root length and root dry weight, nitrogen, phosphorus, potassium, calcium, magnesium, and chlorophyll contents. While Na⁺ and Cl^- were increased relative to control. Also, the results indicated that the salicylic acid, δ-aminolevulinic acid, and triacontanol significantly increased plant growth and chemical traits, as well as reduced the contents of Na⁺ and Cl^- compared to the control (distilled water only) treatment. Application of triacontanol (25 mgL^-1) or salicylic acid (50 mgL^-1); improved vegetative, flowering, root growth and leaves chemical composition under salt stress during both seasons. Triacontanol enhanced salinity tolerance in both seasons by increasing proline accumulation. Under each salinity level, triacontanol (25 mgL^-1) was the most effective treatment for mitigating the deleterious effect of salt stress in pansy plants