Study on the Effect of Cinnamon Extract on Xanthomonas Isolates from Lemon (Citrus limon).

Abstract

In India, citrus industry is the third leading fruit industry after mango and banana. Lemon is one among the important commercial crop of the genus Citrus. Citrus crops are under threat from a variety of factors, including diseases triggered by bacteria, viruses, nematodes, fungi, phytoplasma, and nutritional disorders, which reduce fruit quality and yield. Citrus canker is among one of the most devastating diseases of citrus crop, caused by Xanthomonas citri, affecting all Citrus spp. Controlling measures were restricted to use of copper bactericides with combination of antibiotics. Recent studies showed long-term use of these bactericides has led to the development of copper resistant strains in Xanthomonas citri, resulting in a reduction of disease control. Rather than depending on foliar sprays of copper bactericides for long-term control, new alternative measures must be developed. So, the present investigation was designed to study the effect of cinnamon extract on Xanthomonas isolates from Lemon (Citrus limon). A total of 42 samples showing typical water-soaked edge and erupting canker were collected for isolation, identification and biochemical characterization of causing bacterial disease. Bacteria were isolated on nutrient agar and YDC agar showing yellow coloured, slimy, mucoid, glistening, convex and round colonies after 24 to 48 hours of incubation at 28°C. Further the colonies were purified and preserved on nutrient agar. Results of different biochemical tests showed that Xanthomonas is positive for Ryu’s test, hydrogen sulphide production, starch hydrolysis, citrate test and motility test while negative for Gram’s staining, oxidase test and indole production. So, on the basis of morphological and biochemical results it is confirmed that only 16 samples were positive for native Xanthomonas isolates. The antibiotic sensitivity test was performed by disc-diffusion method. Among different antibiotics, ciprofloxacin showed highest inhibition zone of 38 mm in diameter followed by co-trimoxazole, gentamicin and colistin. Isolates were susceptible for gentamycin (100%), colistin (75%), co-trimoxazole (75%) and ciprofloxacin (62.5%) while intermediately effective against streptomycin and showed resistant to ampicillin, tetracycline and nitrofurantoin. Agar-well diffusion method was used to analysed the in-vitro efficacy of cinnamon extract. All the isolates tested showed sensitive reaction to cinnamon extract while inhibition zone ranges from 17 to 22.4 mm. The highest 22.4 mm of zone of inhibition was measured in diameter, which means the isolates were susceptible to extract. Also, controls showed no zone which indicated that the growth of Xanthomonas isolates was inhibited by cinnamon extract. Thus, cinnamon extract has a potential to be used as alternative antimicrobial agent. The results offer a basis for further work based on the purpose of developing natural antimicrobial agent for control of phytopathogenic bacteria.