| Summary: | 碩士 === 國立中興大學 === 植物病理學系 === 89 === The chitinase plays an important role in the Trichoderma sp. biocontrol mechanism. The fermentation substrates were screened for the chitinase activity of Trichoderma sp. The selected substrate was used as for fermentation and applied to cabbage seedling blight control. Hyphal fragment, conidia and chlamydospores of Trichoderma sp. were all mixed in commercial product. The conidial germination rate was usually too low for biocontrol, so the nutrition or acid was added to stimulate or trigger germination and therefore increase the biocontrol ability. Two application methods of Trichoderma sp. or Gliocladium i.e., drenched into growth substrate and the seed coating were used under different dose of antagonist or pathogen concentrations. As chlamydospore mass production as possible, the biocontrol ability was compared between the chlamydospore and conidia. The chitinase of Trichoderma sp. could be induced in oat solution. The Trichoderma sp. also grew and sporulated well in oat rice hull solid fermentation and exhibited good disease control ability. The number of chlamydospores in oat decoction liquid at 15th day reached 1.25x106 /ml and most of them were matured and detached from the hyphae. The dot-blotting was one of the detection methods of chitinase, but was not sensitive enough to clearly differentiate the quantity of chitinase. The Florence substrate spectrophotometers method was used to detect the minor differently chitinase activity in antagonists. Using 2 % sucrose or PSB could induce the germination of conidia up to 100 % in 24 hr. The antagonistic ability of antagonists that grown on different media was not significantly different, so it could not be used for selection of biocontrol antagonists. Using antagonists that had the same ecology niche with pathogen could not get the better biocontrol results. The inoculum of pathogen prepared in artificial disease substrate made by potato or oat survived well if the substrate was mixed with sand. The solid fermentation products of YT3 or AHS06 had good efficiency to control the disease. Seed coated with antagonist twice had a good control the cabbage seedling blight, unless the growth substrate containing too many pathogen propagules. The G8 and YT3 chlamydospores produced from NyA or CH medium had good control ability on cabbage seedlings blight. The mechanisms involved in promoting the plant growth by Trichoderma sp. are inhibition of minor pathogen, inducing plant resistance, improving the nutritional absorption in rhizosphere, and increase defensive ability to environment stress. However there are still some unknown factors to be explored. The objectives of this study are to find the factor involved in Trichoderma sp. that enhances the cabbage seedling growth. These studies were divided into two parts. The first part of studies was the amendment of Trichoderma sp. into substrate to affect the cabbage seedling growth on plug and gnotobiotic system. The second part of studies was the chitin amendment on plug and gnotobiotic system. At last, combining chitin and Trichoderma sp. application into substrate for promoting seedlings growth and the induction of the PR-1 and PAL m-RNA in rice. When 1 % Trichoderma sp. solid fermentation product was amended, the dry weight of Chinese cabbage and Pakchoi increased more than fold. The rhizoplane competence of Trichoderma harzianum YT3 was observed in tube assay method and it was found that the antagonist sporulated in root cap and root base near stem and no hyphae were observed in root hair. Increment of seedling height was better in coating seed, and root length was performed better by amendment in the substrates with antagonist, while all treatments i.e. seed coating, amendment and drenched into substrates are capable of increase leaf area. After seedlings were transplanted either or not with fertilizer applied the drench by conidial suspension treatment had heaviest dry weight and the seed coating treatment ranked second. In the gnotobiotic condition with exception of isolates YT1, YT2 and P1, to other tested isolates could promote the seedlings growth. Isolates G8, T2 and P3 could enhance seedling growth under fertilization condition. The optimum conidial concentration for seed coating is 107 conidia/seed that could increase the germination rate and the seedlings growth, however if concentration higher than that will be resulted in decrease of germination rate. When substrate was amended with high quantity of chitin at 0.5, 1 or 6 % the seedling flesh weight increased about 50 %. If low quantity of chitin at 0.025 or 0.2 % was added the dry weight increased more than 150 %. Under fertilization the substrates amended with 0.8 or 1 % chitin, the seedling dry weight increased only 37 or 24 %, respectively. When the growth substrate containing the low quantity of chitin and fermentation for 3 weeks, the more chitin added in substrate and the more increase of dry weight resulted. In the gnotobiotic condition the chitin and chitosan amendment increased 16 % and 50 % seedlings dry weight, respectively. In the substrate containing isolate AHS06 could increase 39 % dry weight of seedling and in that substrate mixed with chitin or chitosan could increase 26 or 8 % dry weight, respectively. The chitin powder could increase 173 % seedlings growth in unsteriled peatmoss, but only increase 100 % in autoclaved peatmoss.
|
|---|
