Control Of Bacterial With In Eucalyptus Urophylla By Combinations Of Different Suppressive Mechanisms

Control of bacterial wilt in Eucalyptus urophylla by combinations of different suppressive mechanismsBioassays were performed to control bacterial wilt in Eucalyptus urophylla by salicylic acid(SA), genetically modified strain Pseudomonas putida WCS358::phl, P. fluorescens WCS417r, 2-79, Q2-87 and purified DAPG(2, 4-diacetylphloroglucinol). Based on these, three kinds of experiments were designed to suppress eucalypt bacterial wilt by combinations of different suppressive mechanisms, including salicylic acid with 2-79 and WCS417r, salicylic acid with WCS358:.phl and Q2-87, salicylic acid with DAPG. The percentages of wilted seedlings were significantly decreased when 0.5 mM salicylic acid were applied by root dipping for 3 ~ 5 days before they were transfered to infected hydroponic system or potting soil with Ralstonia solanacearum. Salicylic acid seemed to be poisonous to seedlings of E. urophylla while the concentration exceeded 3 mM or the dipping time was more than 7 days. The control effect on bacterial wilt of strain 2-79, which producs PCA (phenazine-1-carboxylic acid) ,and WCS417r used as a positive control, were tested by dipping roots of seedling in bacterial suspension,followed by transfering them to infected potting soil with R. solanacearum at 5 107CFU.g-1 soil. Strains 2-79 and WCS417r reduced the percentages of wilted seedlings by 18.4 % and 33.8 %,respectively, which was significant compared with that of the control( = 0.05).Strains WCS358::phl and Q2-87,both producing DAPG, were able to suppress eucalypt bacterial wilt effectively both in hydroponic and potting soil.The antibiotics DAPG purified from WCS358::phl and Q2-87, could significantly reduce the percentages of wilted seedlings by 25.8 % and 22.9 %, respectively. Three kinds of combinations with SA plus PCA-producing strain 2-79, SA plus DAPG-producing strains WCS358::phl and Q2-87, and SA plus DAPG,identically gained enhanced protection against eucalypt bacterial wilt, compared with the control and each agent used alone. These results demonstrated that combinations of different suppressive mechanisms, such as induction of systemic resistance and antibiotic, could strongly enhance the control effectc against eucalypt bacterial wilt.