Controlling Of The Bacterial Soft Rot Of Guzmania Denise With Bacillus

687bacterial strains were obtained from rhizosphere soil of Guzmania denise, in which A2strain had a strong antagonism to bacterial soft rot of Guzmania denise. A2Strain was identified as Bacillus subtilis based on its morphological features, physiological and biochemical characteristics and16S rDNA gene sequence.Comparing bacteriostatic potency of strain A2with chemical antibacterials, including agricultural-grade streptomycin, medical-grade penicillin, kanamycin, fenaminosulf, Kasumin-Bordeaux, and chloroisobromine cyanuric acid, we found that A2activity was second only to streptomycin and was more potent than all other tested agricultural chemicals.In a potted seedling trial with bacterial soft rot of Guzmania denise and broth cultures of A2strain at10%,30%,50%and70%densities, the efficiency of A2ability to control bacterial soft rot was70.52%,82.88%,80.39%,81.25%, respectively. Although we did not find significant differences between30%,50%and70%broth densities, all three were significantly more potent compared to10%broth density. Thus, considering cost and other factors,30%broth density appears to be sufficient for effectively controlling soft rot.To understand better how A2strain controls bacterial soft rot, we compared three experimental setups:1) pineapple leaves first sprayed with pathogen broth cultures and24hours later sprayed with A2strain broth cultures2) both bacterial cultures sprayed simultaneously;3) first spraying A2culture and24hours later spraying pathogen broth culture. Observed bacterial soft rot control efficiencies were55.11%,75.51%,82.35%, respectively, indicating that most effective control is observed when A2strain is applied before pathogen application, while applying A2after pathogen application is least effective.Comparing the ability of A2strain to colonize Guzmania denise under three experimental light conditions:24h light;24h dark; and12h light/12h dark, we found that in all three situations, highest colonization occurred on day1and subsequently decreased, stabilizing by day14. Further, while there were no clear differences between colonization at24h light and12h light/12h dark conditions, colonization in24h dark conditions was notably smaller.After inoculation of A2strain onto Guzmania denise leaf, increased activity of host enzymes SOD, POD, PPO, GSH was detected. SOD activity increased by194%; POD activity increased by338%; PPO activity increased by192%; GSH activity increased by215%, indicating that A2strain can induce production of host defense enzymes. Finally, we determined the following optimal growth conditions for antagonistic A2strain:30℃, pH7; optimal inoculation culture age of16～24hours; optimal broth culture growth time of36～72hours; shaker speed150r/min; glucose as the carbon source; ammonium chloride as nitrogen source; and calcium chloride as inorganic salt source.