Biological Control of Leaf Spot Disease by a Few South Indian Medicinal Ferns

Background: Leaf spot is a common disease in agriculture which results in severe yield loss. This harmful disease is caused by a phyto-pathogenic bacteria namely Xanthomonas campestris which is a multi-antibiotic resistant bacterium. Many vegetable and cash crops are severely affected by the leaf spot disease which is caused by X. campestris.These bacteria have acquired resistance to many synthetic pesticides. Pathovars of Xanthomonas are reported to have developed resistance to kanamycin, ampicillin, penicillin and streptomycin. Considering the resistant potency of X. campestris, there is an urgent need for alternative agents for the management of this pathogenic microorganism. Pteridophytes (ferns) are one of the oldest land plant groups on earth and constitute a vast group of vascular cryptograms. Ferns are also show medicinal utility and many of them have been used medicinally from ancient time. The rich diversity of Indian medicinal ferns has been evaluated for their antimicrobial properties, and this may prove benefi cial for mankind. All the parts including rhizome, stem, fronds, pinnae and spores contain antimicrobial and medicinal potency. Hence, in the current study we report the antibacterial activity of ten south Indian medicinal ferns towards X. campestris. Methods: X. campestris was isolated from the infected plant leaves of agricultural fi elds in Tirunelveli, Tamil Nadu, India. The isolation was performed by serial dilution and plating technique on mTBM medium. The isolate was identifi ed on the basis of its morphology and biochemical properties. The isolate was checked for the drug susceptibility by disc diffusion method. Results: X. campestris was found sensitive toward kanamycin (15.70±0.85) and neomycin (16.23±0.47) but resistant to amoxicillin, chloramphenicol, and penicillin. The antibacterial activity of fi ve solvent extracts of ten medicinal ferns collected from the Western Ghats of south India was checked by agar disc diffusion method on MH agar medium. The methanol extracts of all the ferns displayed antibacterial activity against the tested bacteria. Phytochemical analysis of all the extracts revealed that the antibacterial activity may be due to the presence of alkaloids, fl avonoids and phenolic compounds. Conclusions: According to the results of MIC (Minimum Inhibitory Concentration) and RPI (Relative Percentage Inhibition) values, ferns extracts could be used as bio control agents for the management of pathogenic bacteria X. campestris.