Isolation Of Actinomycetes And Its Antagonism Against Banana Fusarium Wilt In The Field

Fusarium wilt of banana, caused by Fusarium oxysporum f.sp. cubense (Foc), is a devastating soil-borne disease affecting banana plantations worldwide. Till date, chemical control of the disease has received little efficiency due to the production of thick-walled, long-living chlamyospores. And the use of chemical fungicides is not recommended because of the potential hazards it caused to the environment. Under this circumstance, biological control, as an environment-friendly approach.Diaoluo Mountain in Hainan Province is one of the pristine tropical rainforests in China,which conserves a substantial amount of microbial resources. In order to screen antagonistic strains against Foc, isolation of antagonistic actinomyces were systematically performed from the soil collected from Diaoluo Mountain. And the biocontrol efficacy in field application was evaluated. The main research results are detailed as follows:1. Sixty-one soil samples were collected at different elevations on Diaoluo Mountain, and385strains of actinomyces were isolated based on traditional separation medium and the designed medium. The designed medium was found to attain better separation efficiency than the traditional medium, in terms of both population and species.2. The385strains of actinomyces were tested for antagonistic activity on plates. As a result,16of the strains were found to be antagonistic to Foc, of which strain DL-28and DL-24showed high antagonistic activity, with inhibition zones of17.2mm and16.8mm in diameter.3. Five strains found with medium or high antagonistic activity were fermented in shake flasks. The fermentation broth of strains DL-28and DL-24were found to have strong antagonistic effect to Foc R4, showing inhibition zones of16.9mm and16.1mm in diameter, respectively.4. The fermentation broth of strain DL-28and DL-24were then further studied to test the stability of antagonistic effect, which showed stable antagonistic effect under the condition of PH4-9, after water bath at5～75℃, and after being exposed to sunlight for48h.5. The antagonistic effects against Foc of the five strains were tested in pot experiment by inoculation on roots and leaves. One hundred days after inoculation, the strains DL-28and DL-24were found with an average control efficacy of83.65%and76.51%to Foc, respectively.6. Field trials demonstrated that the average control efficacy of strains DL-28and DL-24against Foc was47.50%and67.50%, respectively7. Polyphasic classification was performed to identify strains DL28and DL24. Based on16S rDNA sequence analysis and phylogenetic tree, combined with physiological and biochemical characteristics, as well as morphological and cultural characteristics, strain DL24was preliminarily identified as S. misakiensis, and strain DL28was preliminarily defined as S. racemochromogenes.