Divulging the comparing inoculation methods for assessing pathogenicity of Dickeya dadantii inciting stalk rot disease of sorghum

Dickeya dadantii causes bacterial stalk rot of sorghum crop including Maize, a most devastating disease in arid and semi-arid tropics. Saxena et al. (1991), spelled this bacterium causing most destructive diseases of stalk and top rot of sorghum under natural conditions in India during 1987-88 crop season in sorghum field at Pantnagar, Uttarakhand. The disease was wide spread and affected 60-80% of plants in different sorghum genotypes. The disease mainly affects sorghum stem showing water-soaked symptoms that later turn reddish dark brown color. Stalk rot bacterial pathogen was isolated from diseased samples collected from livestock research centre, G.B. Pant University of Agriculture and Technology, Pantnagar. The pathogenicity test was proved on 21 days old sorghum plant in glasshouse. It was found that virulent pathogen developed symptoms with 3 days incubation period and maximum required seven days for development of disease. Preliminary symptoms appeared as water soaked to brown spot on leave and stalk. However, this study was conducted to find out efficient inoculation methods and measured the disease severity for D. dadantii on sorghum and replicability. Bacterial suspension (0.7 % Tween-40 + 2 ⅹ 108 cell/ml) was inoculated with different inoculation techniques, such as (1) Immersion of wounded roots in the bacterial cell suspension (2) Injection of bacterial cell suspension in the base of the stem (3) Leaf- Whorl & Spraying the inoculums by way of hand atomizer (4) Tooth –pick inoculation method (5) Midrib injection method (6) Cotton wool method. Highest stalk rot disease severity (89.75%) was investigated in case of immersion of wounded roots in the bacterial cell suspension method followed by others.