Antibacterial Activity of Essential Oils against Xanthomonas oryzae pv. oryzae Causing Bacterial Leaf Blight of Rice
Rajesh Kampa
Professor Jayashankar Telangana Agricultural University, Rajendranagar, Hyderabad – 500 030, India.
Kiran Babu Talluri *
Professor Jayashankar Telangana Agricultural University, Rajendranagar, Hyderabad – 500 030, India.
G. S. Laha
ICAR-Indian Institute of Rice Research, Rajendranagar, Hyderabad – 500 030, India.
Y. Chandra Mohan
Professor Jayashankar Telangana Agricultural University, Rajendranagar, Hyderabad – 500 030, India.
N. R. G. Varma
Professor Jayashankar Telangana Agricultural University, Rajendranagar, Hyderabad – 500 030, India.
S. N. C. V. L. Pushpavalli
Professor Jayashankar Telangana Agricultural University, Rajendranagar, Hyderabad – 500 030, India.
*Author to whom correspondence should be addressed.
Abstract
Bacterial leaf blight (BLB) of rice, caused by Xanthomonas oryzae pv. oryzae (Xoo), is a major constraint to rice production in tropical and subtropical regions. The common practice of applying antibiotics along with copper-based fungicides for BLB management has resulted in environmental hazards, phytotoxic symptoms in crops and the evolution of resistant bacterial strains. In recent years, essential oils extracted from aromatic plants have gained importance because of their natural antimicrobial properties and eco-friendly nature. Therefore, the present study was undertaken to evaluate the antibacterial efficacy of different essential oils against Xoo under in vitro conditions. A total of eight essential oils, namely neem, eucalyptus, lemongrass, clove, garlic, ginger, black pepper and cinnamon oils, were tested at 5, 10 and 20 per cent concentrations using the disc diffusion assay. Significant differences were observed among the essential oils and concentrations tested. Neem oil recorded the highest inhibition zones of 32.3, 54.0 and 64.0 mm at 5, 10 and 20 per cent concentrations, respectively, with an overall mean inhibition of 50.1 mm. Garlic oil and ginger oil were the next most effective treatments, with mean inhibition values of 37.1 and 32.8 mm, respectively. Antibacterial activity increased with increasing concentrations of essential oils. The present findings indicate that essential oils possess significant inhibitory activity against Xoo and may serve as promising eco-friendly alternatives for the management of bacterial leaf blight of rice.
Keywords: Bacterial leaf blight, disc diffusion assay, essential oils, antibacterial activity, plant-derived bactericides, rice, Xanthomonas oryzae pv. oryzae