Silybum marianum (L.), is an important herbal medicine. Silymarin, the active component obtained from its edible seeds, is known for its antioxidant and antimicrobial activity. This  research was aimed to study the effect of foliar application of salicylic acid (SA) at four concentrations of 1250, 2500, 5000 and 10000 μmol l-1 on the improvement of phytochemical composition, antioxidant and antimicrobial activity. Significant increase was found in the content of silibinin, silybin A and silybin B in plants treated with increasing concentrations of salicylic acid. The antioxidant activity was improved with increasing the SA concentration reaching the highest amount under 5000 μmol l-1 SA treatment (p < 0.05). Irrespective to the bacterial strain, an increasing pattern in the amount of antibacterial activity was found by increasing SA concentration. The study suggest that treatments with medium doses of SA could be a promising way to improve the health beneficial flavonolignans compounds of Silybum marianum resulting in a higher antioxidant and antimicrobial activity. Nevertheless, it should be considered that the responses to SA are highly concentration dependent and application of higher concentrations can have an adverse effect by triggering a hyper sensitive cell death pathway.

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Given the effects of salicylic acid (SA) on enhancing the phenolic compounds, flavonoids, and especially anthocyanins at higher doses in grapes as well as some toxic effects of SA at higher doses, the use of nano-carriers and nano-forms could assist SA in enhancing the accumulation of these compounds while reducing its toxic activity. Chitosan (CTS) has gained attention as a safe transporter and control releaser for a variety of chemicals, particularly in the agriculture industry. In this regard, the nano-form combination of SA and CTS (CTS-SA NPs) could boost the effectiveness of SA, particularly at lower dosages. Therefore, in the present study, SA (10, 20 mM), CTS (0.1%), and CTS-SA NPs (10, 20 mM) were applied on grape (Vitis vinifera L.) berries cv. Red Sultana at the pre-véraison stage to evaluate their actions on phenolic compounds, particularly anthocyanins. The CTS-SA NPs treatments provided the highest results in terms of the total phenolic compounds, flavonoids (10 mM), anthocyanins (in particular oenin, the main anthocyanin of red grapes) (10 and 20 mM), and PAL enzyme activity (20 mM). In conclusion, the CTS-SA NPs could be applied as a potential effective elicitor for phenolics, particularly anthocyanin enhancement of grape berries at pre- véraison stage with synergistic effects between SA and CTS in nano-forms predominantly at lower doses.

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