Costus speciosus (Koen ex.Retz.) is an ornamental plant and has also been used in traditional medicinal systems, mainly in India and Sri Lanka. This research article reveals the antibacterial activity of the leaves of Costus speciosus (Koen.) and its efficacy in different solvents, acetone, ethanol and sterilized distilled water (aqueous), against selected human pathogenic bacteria, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The leaves were tested for antibacterial activity, using agar well diffusion method at the test concentrations of 25, 50 and 75mg/100µl of these solvents, separately. The maximum inhibitory action was observed in ethanol extracts against both bacterial strains at 75mg/100µl concentration. The Minimum Inhibitory Concentration (MIC) for Acetone and ethanol extracts of Costus speciosus were 12.5mg/100µl and 6.25mg/100µl respectively against E. coli whereas it was 12.5mg/100µl against S. aureus for both extracts. The aqueous, ethanol and acetone extracts showed concentration-dependent antibacterial activity against the tested bacteria with the zone of inhibition. Among the solvents used, the acetone showed higher inhibitory activity yet clear and significant inhibition zones were also observed from the aqueous and ethanol leaf extracts. Thereby, the results revealed the medicinal potential of the leaf extracts of Costus speciosus (Koen.) against various infectious diseases to develop a drug with appropriate solvents.

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The study investigated the possibility of enhancing natural disease resistance (NDR) of chili (Capsicum annuum L.), cvs. HYW and CA8, against anthracnose disease, using potassium silicate (Kasil®) as a soil drench or postharvest spray treatment. Anthracnose disease in chili, in this study, was shown to be caused by Colletotrichum acutatum. Potassium silicate (Kasil®), applied as a postharvest spray to the fruit of either cultivar, at 100, 200 and 400 mg/l, reduced anthracnose development significantly (p = 0.05) when the fruits were challenge-inoculated 3 days after treatment. Treatment was slightly more effective at 200 mg/l. There was 100% of reduction of anthracnose in treated fruits of cv. CA-8 throughout an 8 th day period of storage following fruit inoculation. In the cv. HYW, the same treatment showed 100% disease reduction only initially, 4 days after inoculation. The treatment was also applied as a pre-harvest soil drench commencing from flower initiation, at 200 mg/l, weekly for 4 weeks. The treatment reduced anthracnose disease significantly (p = 0.05) in harvested fruits, challenge-inoculated with C. acutatum. Spore germination assay revealed that potassium silicate had no antifungal effect to C. acutatum. Potassium silicate (Kasil®)-treated fruits, inoculated with C. acutatum after harvest, showed greater accumulation of phytoalexins and increased level of β-1, 3-glucanase in fruit tissue.

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