Survival of the Carambola Strain of Pseudomonas syringae and the Potential Disease Control by an Antagonistic Bacterium Pantoea dispersa CL166

• Main Authors: Ming-Ling Liao, 廖敏伶
• Other Authors: Shih-Tien Hsu
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/75086503057491484480

碩士 === 國立中興大學 === 植物病理學系 === 90 === Bacterial spot, caused by the carambola strain of Pseudomonas syringae, is a new disease of carambola in Taiwan. Little information on the ecology of the pathogen is known. The survival of the pathogen and possible control of the disease by an antagonistic bacterium were investigated in the study. A rifampicin resistant mutant (PA5r) of the pathogen was used in the survival studies. In the loam soils collected from Dungshr and Juolan, population of PA5r declined rapidly regardless of the soil moisture contents tested. It survived better under low temperature and near neutral to slightly alkaline soil conditions than under warm and low pH conditions. Soil temperature and moisture influenced survival of PA5r associated with carambola leaves. At 28 ℃, viable cells of PA5r were recovered after 70 days in lesions of carambola leaves placed on the surface of Dungshr and Juolan soils containing various water contents, except Dungshr soil containing 31.2% soil moisture. At 16 ℃, PA5r populations in lesions remained almost unchanged under all soil moisture regimes. Five weeds species were assayed for PA5r epiphytic population. With artificial inoculation, PA5r survived better on Oxalis corymbosa and Solanum nigrum leaf surfaces with populations remained at 102 - 103 cfu/cm2. In carambola stems, PA5r survived more than three months with populations at the range of 104 - 105 cfu/g. Saprophytic bacterial isolates from carambola leaves were tested in vitro for their antagonistic activities against carambola strains of P. syringae and in vivo for their abilities to suppress the disease. Only one of the isolates was effective. This isolate (CL166) was identified as Pantoea dispersa. In greenhouse tests, P. dispersa CL166 significantly reduced the disease severity of bacterial spot of carambola when applied prior to the pathogen, but not when applied together with the pathogen. In addition, P. dispersa CL166n (nalidixic acid resistant mutant) reduced populations of P. syringae PA5r in carambola leaves when the antagonistic bacterium was inoculated in advance of the pathogen, but not when it was coinoculated with the pathogen.