Abstract
Purpose: To investigate the effect of salicylic acid (SA) on the antimicrobial profile of Stevia leaf extracts against soybean seed-borne pathogens. Methods: Stevia seeds were planted in a greenhouse and SA foliar applied after six weeks on the whole plant at concentrations of 0 and 0.1 g L -1 . The extracts of the plant leaf were separately obtained using four different solvents (water, acetone, ethanol and chloroform), and the oil composition of the extracts determined by gas chromatography-mass spectrophotometry (GC-MS). The antibacterial and antifungal potentials of each of the extracts were examined against 11 selected pathogens responsible for soybean seed and seedling diseases. Results: Chloroform extrac -cadinol, spathulenol, caryophyllene oxide, methyl salicylate and safranal in the SA-treated plants, and were 8, 10, 18, 14 and 11 %, respectively, higher than the non-SA treated control. In the anti-microbial tests, chloroform extract exhibited the highest diameter of inhibition zone (max 18 mm) against all the tested microorganisms while water extract showed the least effect (max 9 mm), with no effect at all on two fungi (Phomopsis spp and Cercospora kikuchii) and two bacteria (Pseudomonas syringae and Xanthomonas campestris). All extracts with or without SA had no effect on Xanthomonas campestris. SA treatment enhanced the antimicrobial potential of all extracts in the pathogenicity test compared with untreated plant extracts. Conclusion: Stevia leaf extract has antimicrobial effect against soybean seed-borne disease if applied on the seed before planting. Application of SA on the Stevia plant substantially enhances the antimicrobial activity of the leaf extract thus affording the seeds greater protection.
Highlights
Stevia (Stevia rebaudiana Bertoni) is a slender, small and perennial herb, belongs to Asteraceae family
Application of salicylic acid (SA) on the Stevia plant substantially enhances the antimicrobial activity of the leaf extract affording the seeds greater protection
Tropical Journal of Pharmaceutical Research is indexed by Science Citation Index (SciSearch), Scopus, International Pharmaceutical Abstract, Chemical Abstracts, Embase, Index Copernicus, EBSCO, African Index Medicus, JournalSeek, Journal Citation Reports/Science Edition, Directory of Open Access Journals (DOAJ), African Journal Online, Bioline International, Open-J-Gate and Pharmacy Abstracts
Summary
Stevia (Stevia rebaudiana Bertoni) is a slender, small and perennial herb, belongs to Asteraceae family. Its introduction as a natural and noncaloric sweetener has increased the options of available sweeteners, especially for the diabetic population [1]. This plant is a rich source of stevioside that is 100 - 400 times sweeter than sucrose [2, 3]. Besides the use of stevia as a sweetening agent, there are some reports on the antimicrobial activity of leaf extracts that makes it an important medicinal plant [4,5,6]. Due to the increasing emergence of resistant pathogens, scientists have shown increased interest in identifying new phytochemicals to tackle plant diseases. Stevia leaf extracts contain some phytochemicals such as phenols and flavonoids
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