| Biocontrol agents Bacillus amyloliquefaciens LJ02 was isolated from soil. LJ02 could inhibit myriad pathogen fungus. LJ02 fermentation broth(LJ02FB) could effectively diminish the occurance of grapes and cucurbits powdery mildew by leaf spraying in greenhouse. In this paper, cucumber was used as a target plant to explore the bicontrol mechanism of LJ02 FB against cucumber powdery mildew. Futhermore, the quantity of fungi in rhizosphere soil and the inhibition rate of rhizosphere medium against fungi were detected after treated with LJ02 FB in cucumber cotyledons. Moreover, LJ02 FB was separated into two components: cell-free fermentation suspension(LJ02FS) and bacterial cell pellet(LJ02BC). Then the cotyledons of cucumber seedlings were sprayed with LJ02 CS and LJ02 BS separately in two groups at trefoil stage, subsequently HPLC and real-time PCR were used to examine the effects of both fractions(LJ02FS and LJ02BC) on the production of free SA and PR gene in cucumber tissues with spatial and temporal scales. Finally the plasmid p Mar A was used to explore the chemical-transformation and electro-tansfomation efficiency of LJ02. The main results are as follows:1. Greenhouse trails showed the control efficacy on cucumber powdery mildew of 69.8%, 86.44% and 85.05% after treated by LJ02 FB for 7, 14 and 21 days, respectively.2. After treated with LJ02 FB in cucumber cotyledons, the quantity of rhziosphere fungi at 7th and 14 th day decreased to 3.2×104 CFU/g and 3.5×104 CFU/g, respectively. The rhizosphere MS solid medium of LJ02FB-treated cucumber could strongly inhibit the growth of target pathogens. The diameter of inhibition zone is 0.9 cm for F. oxysporum, 1.6 cm for B. cinerea and 1.1 cm for Alternaria spp. The final germination rate is about 11.1% for F. oxysporum, 0.1% for B. cinerea and 1.6% for Alternaria spp.3. Both LJ02 FS and LJ02 BC could induce the production of free SA in systemic tissues. While the amount of SA in roots was lower as compare to that of leaves.4. PDB fermentation broth could significantly induce the the expression of PR genes. Futhermore, both LJ02 FS and LJ02 BC could induce the expression of PR-1 gene. LJ02 FS could induce the expression of PR-2 and PR-3 gene. LJ02 BC could induce the expression of PR-9 gene.5. When the OD600 of growth medium reached 0.9 with a 1.8kv/cm pluse, the electro-transformation efficiency reached 180CFU/μg. When the OD600 of SPII medium reached 1.2, the chemical transformation efficiency reached 23.3CFU/μg.Altogether, the result proved that LJ02 FB strongly inhibited the occurance of cucumber powdery mildew with a long-term effect under greenhouse condition. Futhermore, LJ02 FB could induced cucumber secret resistance-related substances into rhizosphere against a wide range of fungi pathogen. Moreover LJ02 FB could induce resistance with the SA signal pathway and the SA signal prefernce to transmit from roots to leaves. While different elictiors of both fractions were involed in resistance induction. LJ02 BC could induced resistance with the JA/ET pathway and LJ02 FS induced HR-related enzyzmes. In addition, LJ02 showed excellent capacity in forming competent cells for genetic transformation. |
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