Aim: The aim of our study is to isolate, identify and pathogenicity test of Xanthomonas axonopodis pv. malvacearum (Xam) causing bacterial blight of cotton and to determine the comparative efficacy of some selected chemicals and antibiotic in controlling Xam in vitro.

Place and Duration of the Study: This study was carried out at the Department of Plant Pathology, Sher-e-Bangla Agricultural University, Dhaka, Bangladesh from January, 2012 to December, 2013.

Methodology: Xanthomonas axonopodis pv. malvacearum was isolated from infected leaves, stems, branches, cotyledons and bolls of cotton. Biochemical characterization and in vitro sensitivity were evaluated as per the standard methods as described in materials and methods.

Results: The bacterium was gram negative, rod shaped and showed positive results in KOH solubility, starch hydrolysis, catalase, citrate utilization, motility indole ureas agar (MIU), gelatin liquefaction test and oxidase test. It produced, slightly raised, blond to bright yellow colour, mucoid colonies on NA medium; circular, flattened or slightly raised, yellow to bright yellow colour, mucoid colonies on YDCA medium and light yellow, mostly circular, slightly flattened on SX medium. In vitro evaluation of selected chemicals revealed that Streptomycin sulphate was highly effective against Xam. In in vitro condition, the highest inhibition zone (35.33, 36.17, 35.17, 33.5 and 32.33 mm after 24, 48, 72, 96 and 120 hrs. respectively) was observed in Streptomycin sulphate @ 0.15% treated plates.

Conclusions: Streptomycin sulphate showed higher effectivity against X. axonopodis pv. malvacearum compared with selected fungicides.

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