Bacteriophages : Characterization and Utilization as Biocontrol Agents Against Xanthomonas Axonopodis pv. citri (Hasse) Vauterin et al. And Ralstonia solanacearum (Smith) Yabuuchi et al.
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Date
2015-10
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University of Agricultural Science, Dharwad
Abstract
Citrus canker and solanaceous bacterial wilt are the most devastating diseases which leads to heavy economic losses. In present study, bacteriophages are used as biocontrol agents against Xanthomonas axonopodis pv. citri (Xac) and Ralstonia solanacearum. Five native cultures of Xac and R. solanacearum were isolated, confirmed for their pathogenicity and molecular identity.
Three phages of Xac (Xacpv1, Xacpv2 (phylloplane) and Xacpv3 (rhizosphere)) and two phages of R. solanacearum (Rspv1 (pond water) and Rspv2 (rhizosphere)) were isolated. Host range studies revealed Xacpv1and Rspv1phages with broad lytic activity on their respective hosts. All the Xac and R.solanacearum phages were chloroform insensitive and non-specific to other tested bacteria. Xacpv3 and Rspv2 phages completed their entire life cycles in 70 and 90 min with average burst sizes of 25 and 85 Plaque Forming Units (PFU) per infected cell respectively. Phage morphology of Xacpv1 and Xacpv2 showed icosahedral heads with short tails (Podoviridae). Xacpv3 and Rspv1 showed an icosahedral heads with long contractile tails (Myoviridae) and Rspv2 appeared in long contractile fibers (Inoviridae). RAPD analysis with four random primers showed that all the Xac and R. solanacearum phages were diverse in nature.
In phage stability studies, Xac phages on citrus phylloplane population rapidly came down after four days of application from 8 to 3 log PFU/ml. Significant difference between formulated and unformulated phages was observed after eight days of application. In rhizosphere of tomato seedlings, both formulated and unformulated phages of R. solanacearum retained high phage concentration for 16 days. In glasshouse studies, the per cent disease reduction of citrus canker over control was maximum (61.55%) in T3 (Copper oxy Chloride (0.3%) + Streptocycline (500 ppm)) followed by T4 (Phage mix) (58.59%). The seedling stages of both tomato and brinjal phages performed better than other individual components of IDM in reducing bacterial wilt.
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