In a separate platedmedium, Xoo suspensions (approx. 106cfu/mL) were seeded uniformly using pour plate method. Five equidistantwells were made in the previously plated medium seeded with Xoo by using asterilized cork borer and using a sterile syringe of a 0.1 mL of rhizobacteria(108cfu/mL) was placed onthe wells. The assayed plates were incubated for 24 to 48 hours and the zonesof growth inhibition of Xoo around the rhizobacterial antagonists were measured(Beric et al., 2012).
In vivo Screening of the Potential RhizobacteriaDifferent isolates of the rhizobacteria that inhibit the growth of Xoo under in vitrotest were separately applied to rice seeds of NSIC Rc224. The seeds were soakedin 0.01% polyoxyethylene–sorbitan monolaurate (Tween20, Sigma, Aldrich) containing 108cfu/ mL ofthe rhizobacterial antagonist, and thenkept at 28°C for 48 hours. The controlseeds (without rhizobacteria) were soaked in sterile water. Subsequently, bothcontrol and treated seeds were sown in seedbedsusing natural field soil.
Seedlings were transplanted into plastic pots after21 days. At the time of transplanting, the seedlings were root dipped intorhizobacterial antagonist suspension containing 108cfu/mL andsterile distilled water for control. Foliar sprays of each rhizobacterial antagonistwere applied 28 and 35 days after transplant ng (DAT). Inoculation of bacterialleaf blight (BLB) pathogen was done at 40 and 45 DAT using leaf cutting method(Gnanamanickam, Velusamy, & Immanuel, 2013, pp.356362). Percent of diseasesuppression was calculated by measuring the mean lesion length of theinoculated control plants minus the mean lesion length of the rhizobacterialantagonist treated plants over the mean lesion length of the inoculated controlplants multiply by 100.
There were 20 random plants with three replications inthese experiments. Table 1 shows that the disease severity was evaluated 18days after inoculation (DAI) up to 56 DAI with seven days interval followingthe modified rating scale of International Rice Research Institute –Standard EvaluationSystem for BLB percent infection following the formula: