Biocontrol of stem rot of Taiwan Anoectochilus caused by Fusarium oxysporum Schl.
| Autor: | Chin-Chih Tsai, 蔡金池 |
|---|---|
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 96 For the biological control of stem rot of Anoectochilus formosanus Hayata caused by Fusarium oxysporum Schl., a total of 5 antagonistic Trichoderma strains were isolated from A. formosanus rhizospheres in Puli. The potential of the obtained strains as biocontrol agent were evaluated by dual culture assay against Fusarium oxysporum Schl. F66 strain on potato sucrose agar. The characteristics screened included inhibition of mycelial growth for the pathogen, the growth and sporulation of the antagonists, and the growth promoting effect on target plant. A followed field trial at Puli, Nantou, aimed for the control of Fusarium stem rot of A. formosanus indicated Trichoderma TA strain was the best among the five strains in regard to the yield and the disease control effectiveness. In a greenhouse trial, the effectiveness of stem rot control was shown dependent on the conidial concentration of the antagonist applied. The stem rot incidence of test plants grown in substrates treated by 5.7Χ106-107 cfu/gram conidial preparation 15 weeks after treatment was approximately 10%, whereas that of the compared non-treated control was about 93.3%. In a serial field trials, the effectiveness of disease control was consistently found better by root coating or preplanting substrate blending with the conidial suspension than that by the chlamydospore preparation of the antagonist. A conidial formulation with carboxymethyl cellulose (CoCMC) was most effective for the disease control in practical cultivation. By root coating during transplanting, the application of CoCMC resulted in nearly 100% protection of the test plants for 9 weeks, whereas the disease incidence of non-treated control at the same time reached about 82 %. The protective effect of CoCMC appeared to be further strengthened by the addition of wheat bran as a food base. The Trichoderma/ Fusarium population dynamics contained in the growth substrates indicated a well sustained Trichoderma population at approximately 107 cfu/g throughout the test period. And in accompany to that was the decrease of disease incidence. These results suggest T. asperellum TA strain have an excellent potential to be used as biocontrol agents for the control of stem rot disease of A. formosanus. Investisation of the biological characteristics of TA strain indicated that the fungus produced chlamydospores on culture and showed optimum and maximum mycelial growth temperature at 30 and 37℃, respectively. It may utilize melezitose as sole carbon source and produce antifungal isonitrinic acids and unique coconut smells. Also, upon conidiation, it produced conidiophores predominantly in paired branching, and among them bore slender-ampulliform phialides with characteristic viride-type morphology. The conidia were ovoid to subglobose structure covered with conspicuous irregular pyramidal warts. The morphological characteristics indicated TA strain a member of T. asperellum (Samuels, Liechfeldt & Nirenberg). By polymerase chain reaction, the rDNA internal transcribed spacer (ITS) sequence of the TA strains was amplified and sequenced. Results obtained from the pair-wise comparison of the sequence data of comparative strains available from NCBI and the phylogenetic analysis supported fully the above species identification based on the morphological characteristics. The involvement of induced resistance in the effectiveness of T. asperellum TA strain as a biological agent for controlling stem rot of A. formosanus caused by F. oxysporum Schl. was explored. For A. formosanus grown in a gnotobiotic culture system, inoculation of a TA strain germinating conidial suspension (8.3X105 conidia/ml) was shown leading to transcient but significant increases of activities of phenylalanine ammonia lyase, peroxidase, chitinase, and β-1,3-glucancase, and as well the accumulation in cell wall free soluble phenolics, and lignin among leaves, stem and root tissues of treated A. formosanus. Similar stimulatory effects were also observed on test plants treated with culture filtrate of TA strain grown in 1% (w/v) cell wall of F. oxysporum or chitin. Whereas that among control plants treated with non-cultured broth medium were not detected. In the case of changes of phenylalanine ammonia lyase and peroxidase activities, the stimulatory effect was also detected by treatment with 2,6-dichloroisonicotinic acid- the chemical known to provoke systemic acquired resistance on various crop species. The stimulatory effects detected on stem and leaf tissues indicated the systemic effect of the treatment which was applied primarily on the roots. The accumulated data indicated the importance of systemic aquired resistance as a major factor contributing to the effectiveness of biological control of stem rot disease by T. asperellum TA strain. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|