The biocontrol mechanism and integrated pest management of Streptomyces plicatus B4-7 on controlling Phytophthora capsici

• Main Authors: Ying-Yu Chen, 陳盈宇
• Other Authors: 蔡東纂
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/06286229340231269581

博士 === 國立中興大學 === 植物病理學系所 === 104 === A Streptomyces plicatus B4-7 was obtained from the bamboo leaf in a citrus farm (Qionglin Township, Hsinchu County, Taiwan) and identified by 16S rDNA methods. B4-7 suppressed up to 75% mycelial growth of Phytophthora capsici, P. cinnamomi, P. palmivora and P. parasitica in the dual culture test on PSA (potato sucrose agar) plates. The hyperparasitism of B4-7 against P. capsici was confirmed under the scanning electron microscope. The cultural filtrates of B4-7 in chitin-potato sucrose broth, potato sucrose broth, rice bran broth and oatmeal broth can inhibited the mycelial growth and the zoospore germination of P. capsici in the in vitro tests. Abnormal formation of P. capsici zoospore germ tubes were observed after treated with B4-7 cultural filtrates 24 h. When the B4-7 cultural filtrates and P. capsici zoospore were inoculated simultaneously on bell pepper leaves, 100% disease suppression was observed. In the pot test, the B4-7 OM cultural broth when added 3 h post inoculation (HPI) of P. capsici showed 75% crown rot disease reduction. The OM cultural broth was extract with ethyl acetate, and the EA supernatant was purified by column chromatography eluted with ethyl acetate/hexane as the developing solvent system. A compound was isolated from the anti-Phytophthora fraction of B4-7 OM broth, and was identified as borrelidin according to the spectral analysis. This study is the first report of S. plicatus capable of producing this antibiotic. Borrelidin isolated from B4-7 showed 50%, 92.86% and 100% inhibitory to the mycelial growth of P. capsici when treated 1, 5 and 10 mg/L for 24 h, respectively. The results indicated B4-7 could be a good biocontrol agent candidate for the integrated pest management (IPM) program to control Phytophthora blight. To evaluate the potential of Streptomyces spp. applied in an integrated pest management system, commonly used pesticides from different pesticide categories were tested in vitro and in vivo for the compatibility. Two biocontrol actinomycetes, Streptomyces saraceticus strain 31 and S. plicatus B4-7, were used to control Meloidogyne incognita and Phytophthora capsici, respectively. In the in vitro test, 73 pesticides were tested with SS31, and 12 with B4-7. When the pesticides applied with Streptomyces spp. at the same time in vitro (S1), SS31 was found to be compatible with 40 out of 73 pesticides tested, and 4 out of 12 for B4-7. The in vitro test results indicated that when SS31 and B4-7 were established 24 h before the pesticide application (S2), the inhibition effects of the pesticides were reduced. Under the S2 treatments, 55 pesticides were compatible with SS31, and 8 with B4-7. SS31 could lower both the M. incognita galling index and J2 population in greenhouse trials, and was compatible with chlorothalonil, copper hydroxide, ethoprop and carbofuran regardless of the pesticide application sequences. Application of B4-7 mixed with etridiazole or copper hydroxide on controlling P. capsici in vivo showed the pesticides could achieve the same control efficacies at lower dosage. Both SS31 and B4-7 compatible with the majority pesticides when applied in the field with an appropriate time interval are suitable BCAs for the IPM.