Control of Orange Green Mold with Gas-Producing Bacteria and Analysis of Their Major Gas Components Suppressing the Pathogen

• Main Authors: Po-Sung Chen, 陳泊菘
• Other Authors: Jenn-Wen Huang
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/83717482307393086027

碩士 === 國立中興大學 === 植物病理學系所 === 97 === Orange green mold incited by Penicillium digitatum causes a great part of postharvest losses on orange fruits. Fungicides are the primary means of controlling postharvest diseases. However, multiple drug resistant strains of postharvest pathogens have occurred due to frequently use of traditional chemical treatments and limited their effectiveness. In addition, methyl bromide, a fumigant that commonly used in post-harvest management of pests and pathogens on fresh products and durable commodities, has been suggested to be banned by the Montreal Protocol. Thus, finding an alternative way in safe means to humans to displace methyl bromide in postharvest management might be needed. The main purpose of this research is to evaluate a useful biocontrol formulation for producing gas by four strains of gas-producing bacteria, Enterobacter cloacae isolates E006、E010 and Bacillus mycoides isolates CHT2401、CHT2401, to control orange green mold. In vitro tests, E. cloacae E006 and E010 grown on plates of King’s medium B (KB) and B. mycoides CHT2401 and CHT2401 grown on plates of Tryptic soy agar (TSA) were conducted for suppressing conidial germination and mycelial growth of Penicillium digitatum P51 and DOB-2. E. cloacae E010 and B. mycoides CHT2401 expressed better effectiveness in inhibiting the two pathogens. Temperature at 24℃ was optimal for E010 and CHT2401 releasing gas to inhibit conidial germination of P51 and DOB-2 compared to the control. KB at pH6 for culturing E. cloacae E010 and TSA at pH7-8 for culturing B. mycoides CHT2401 were the most optimal for two bacteria to release gas for inhibiting conidial germination of P51 and DOB-2. Gas released from perlite mixed with KB or TSB ingredients culturing E. cloacae E010 or B. mycoides CHT2401 (E010-KB-Perlite formula, EKP; CHT2401-TSB-Perlite formula, CTP) was effective in reducing disease severity of orange green mold caused by P. digitatum P51 from 80% to 0% or from 90.0% to 18.9%, respectively. The amount of 150mL EKP or CTP which added 2.5 times amount of original KB or TSB ingredients was the best substrate for culturing E010 and CHT2401 to produce gas for controlling orange green mold. After the fruits were treated with the EKP or CTP for 7 days, development of disease lesions on P. digitatum P51-inoculated orange fruits was much slower compared to the other treatment. Adding 5 times amount of KB ingredients to EKP could prolong the gas-releasing period of the bacterium to control orange green mold for one month. Comparison of gas-producing bacteria incubated in EKP or CTP and chemical treatments (thiabendazole and benomyl) showed that gas-producing bacteria incubated in EKP or CTP was much more effective in controlling orange green mold than chemical treatments. Only E. cloacae E010 incubated in EKP could successfully inhibit disease development under low temperatures (8-16℃). The volatile organic compounds (VOCs) produced by E. cloacae E006 and E010 on KB plate or KB-mixed perlite formula were identified by Gas chromatography- mass spectrometry. The major VOCs produced by E006 and E010 were identified as phenylethyl alcohol、butyl actate and 4,5-dimethyl-1-hexene. In our studies, 4,5-dimethyl-1-hexene was supposed to be a major compound for inhibiting conidial germination of P. digitatum P51 by E006 and E010. The major VOCs produced by B. mycoides CHT2401 and CHT2401 was identified as dimethyl disulfide. Dimethyl disulfide was able to significantly suppress P. digitatum P51 conidial germination and mycelial growth in vitro and completely control orange green mold caused by P. digitatum P51 in vivo tests.