제주에서 근권세균을 이용한 주요 식물병의 방제

Abstract

The most popular method to control the diseases has been to apply chemical fungicides. However, environment favorable plant protection comes to the fore as another method, and the number of eco-friendly crop cultivation has been gradually increased in Jeju, where the application of the synthetic organic fungicides is forbidden. Therefore, an alternative strategy to protect various plant pathogens is strongly required in organic farms. Plant growth promoting rhizobacteria(PGPR) has been known as a biological inducer of resistance against various plant pathogens in many crops. Also biological control of plant diseases was conducted using antagonistic bacteria after having been selected through sequential screening procedures in laboratory. Bacterial strains were isolated from the rhizosphere of annual plants growing in Jeju. In total, 12 bacterial isolates were selected from over 100 bacterial isolates through the tests on resistance induction or biological control efficacy against various plant diseases. Protective effects to many diseases in crop plants by bacterial isolates were investigated. And resistance mediated by bacterial isolates against various plant diseases were tested in annual crop plants such as cucumbers, potatoes, tomatoes, and peppers. The bacterial isolates were identified through the analysis of the ribosomal DNA sequence in the internal transcribed spacer(ITS) region. Using universal primers 38r and 72f, all the bacterial DNA samples were amplified. Among the effective bacterial isolates, 42% were belonged to genus Bacillus. Three of them were identified as B. cereus and other 2 isolates as B. weihenstephanensis and B. circulans in genus Bacillus. Three isolates were identified as Burkholderia gladioli. And the other 4 isolates were identified as Acinetobacter Quenomosp, Miamiensis avidus, Pseudomonas fluorescens and Pseudomonas putida. In the first study, bacterial strains isolated from rhizosphere of plant were tested whether they could suppress citrus canker on citrus leaves. Among 17 bacterial strains, 4 bacterial isolates such as MRL408-3, TRH423-3, TRH415-2, and THJ609-3 showed antibacterial effects against citrus canker pathogen in vitro and suppression of disease severity on the leaves, compared to the single inoculation treatment with suspension of the citrus canker pathogen in vivo test, and in the field experiments. In the second study, suppression effect against late blight caused by Phytophthora citrophthora of the 12 bacterial isolates from plant rhizosphere were investigated on citrus fruits. Among the 12 bacterial isolates, THJ609-3, TRH423-3, BRH433-2, TRL2-3, and KRY505-3, disease suppression was confirmed, after having wound inoculation with the fungal pathogen in vivo. Disease severity was determined by measuring the lesion diameter on the inoculated sites of the citrus fruits. In the third study, 4 bacterial isolates such as THJ609-3, TRH415-2, MRL408-3 and TRH423-3, known as effective microorganism for biological control to the melanose of citrus were investigated in vitro as well as in vivo test. Disease severity of melanose caused by Diaporthe citri was measured up by the number of the appeared lesion on the citrus leaves, spray-inoculated with mixture of Diaporthe citri and the bacterial isolates. Only a few lesions were found on the leaves inoculated with mixture of Diaporthe citri and the suspension of the bacterial isolates, respectively. In the fourth study, 4 bacterial isolates as BRH433-2, TRH423-3, TRH415-2 and MRL408-3 were selected through the antagonistic activity against garlic white rot caused Sclerotium cepivorum Berk. and testing of resistance induction efficacy against various plant diseases with priority. The highest anti-fungal activity was evaluated by the inhabitation of hyphal growth of plant pathogens adjacent to bacterial isolates as BRH433-2 and TRH423-3. Disease suppression increase of the garlic bulbs on the garlic plant, in these 4 pre-treated bacterial isolates, were higher than the non-bacterized control plants in vivo test. In the fifth study, it was investigated that the antagonistic effect of the bacterial isolate TRK2-2 against late blight in tissue culture after its pre- or post treatments. Pre-treatment of the bacterial suspension to 1 or 3 days before the fungal inoculation caused suppression of disease severity of late blight, whereas post-treatment behind 2 hours after pathogen inoculation did not control. In pre- or post treatments of DL-3-amino butyric acid (BABA), a well-known resistance inducer, similar results were shown, with those of TRK2-2. Based on these results it is suggested that the effective bacterial isolates may be very useful to find biological control efficacy or resistance induction agents against major diseases in various crop plants, especially on environment-friendly farm where the application of fungicide was limited.