Effect of salicylic acid on the growth, metabolic activities and oil content of basil and marjoram

The response of sweet basil (Ocimum basilicum L.) and marjoram (Majorana hortensis) plants to foliar application of salicylic acid (SA) at 10-5, 10-4 and 10-3 M was determined in pot experiments conducted during 2004-2005. SA increased plant height, number of (branches, nodes & leaves) per plant, leaf area, fresh and dry weight of herbs, total carbohydrates, crude protein, total amino acids, free proline, photosynthetic pigments as well as microelement content and uptake up to 10-4 M relative to un-treated controls and decreased thereafter both in basil and marjoram. All SA treatments enhanced putrescine, spermidine as well as total polyamines contents, while reduced the level of spermine in both plants. Oil percentage and yield per plant for three cuttings also increased about two folds on a fresh weight basis with SA application at 10-4 M in case of basil and 10-3 M in marjoram relative to un-treated controls. GC/MS revealed that common components of Ocimum basilicum essential oil under all treatments were linalool (46.63 - 43.32%), methyl eugenol (13.83 - 5.68%), 1, 8 - cineol (13.20 - 4.43%), eugenol (12.64 - 7.16%) and alpha-cadinol (9.59 - 4.46%). SA at 10-4 M increased the production of top quantity and quality of basil oil to the fragrance and food industries by increasing the percentage of eugenol and antioxidant activity in the herb. On the other hand, the marjoram essential oil contains cis-sabinene hydrate (37.50 - 14.27%), terpinen- 4-ol (24.33-13.99%), p-cymene (18.21 - 2.29%), sabinene (17.69 - 4.11%), gamma-terpinene (10.64 - 4.77) in addition to alpha-terppnenl (5.52-3.96%), trans-sabinene hydrate (5.45 - 8.19%), alpha-terpinene (2.41 - 0.00%) and (beta-caryophyllene (3.82-1.76%). Moreover, SA 10-5 M and 10-3 M improved oil quality by increasing the level of sabinene accompanied by a decrease in the proportion of cis-sabinene hydrate relative to controls. The data suggest that in both species , SA treatment especially at 10-4 M may have higher adaptive capacity to stress, originating from promoting polyamines synthesis and better osmotic adjustment.