| Summary: | 碩士 === 國立中興大學 === 植物病理學系所 === 102 === Phytophthora blight of bell pepper caused by Phytophthora capsici Leonian is one of the most important diseases occurred in pepper cultivation. It causes dramatical economic loss of bell pepper production in warm and humid conditions. The most applied strategy for disease management is frequent application of chemical pesticides which results in environmental pollution and food safety issues. The purpose of this study was to develop microbial agents for controlling Phytophthora blight of bell pepper. Out of the 85 isolates originated from salvinia (Salvinia molesta D.Mitch.) plants, two isolates, namely SM64 and SM69, showed strong inhibitory effect on the mycelial growth of P. capsici Pc28089 on nutrient agar plate, with the inhibition of 71.8% and 70.1%, respectively. SM64 and SM69 were respectively identified as Paenibacillus polymyxa (Prazmowski) Ash et al. and Bacillus amyloliquefaciens (ex Fukumoto) Priest et al. according to the results of biolog assay, and the sequences of partial 16S rRNA , and 16S-23S rRNA internal transcribed spacer. When the pathogen was treated with 4-day-old culture liquid of SM64 or SM69 in nutrient broth (NB), the zoospores were destroyed and their concentrations were markedly reduced by 59-98%. The culture liquid of SM64 or SM69 in NB amended with 2% (w/v) sucrose or 3% (w/v) soybean meal medium (SMM) could completely suppress disease development on detached pepper leaves. Screening of the best medium for culturing SM64 and SM69 was conducted by treating zoospores of P. capsici with 4-day-old culture liquid on sterile slides. The culture liquid of SM69 in soybean meal-molasses medium (SM) significantly reduced zoospore germination of the pathogen, but SM64 in SM culture liquid did not inhibit zoospore germination. However, the SM69 culture liquid at 100-fold dilution could still reduce zoospore germination by 38%. Analyzing antifungal substances from fermentation filtrate of SM69 by high pressure liquid chromatography (HPLC), iturin A-like and surfactin-like compounds could be detected. The 200-fold diluted culture liquid of SM69 in soybean meal-sucrose medium (SSu) amended with 2.5% (v/v) soybean oil significantly reduced the disease index from 4 to 1 compared to the control. After spraying 200-fold diluted culture liquid of SM69 in SSu medium or SSu amended with 2.5% (v/v) soybean oil on bell pepper seedlings at greenhouse condition, treatment of culture liquid of SM69 in SSu medium amended with soybean oil, sprayed at one day after-inoculation, showed the best disease suppression effect among all treatments, resulting in reduction of disease index from 3 of the control to 1.6. Based on results from assays on detached pepper leaves or pepper seedlings, it suggested that the bacterium, B. amyloliquefaciens isolate SM69, has great potential to be developed into microbial agent for controlling Phytophthora blight of bell pepper.
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