| Summary: | 碩士 === 國立中興大學 === 植物病理學系 === 89 === Damping-off caused by Pythium aphanidermatum is a serious disease of watermelon seedlings grown in the container medium. Spent forest mushroom compost (SFMC) was tested for its effect on damping-off of watermelon seedlings caused by P. aphanidermatum. SFMC was effective in inhibiting damping-off, however, it slightly reduced the growth of watermelon seedlings. Six materials such as BVB No.4 peat moss (BVB), coconut fiber, perlite, vermiculite, TKS-2 peat moss (made by Floragard Vertriebs Gmbh), and carbonized rice hull were respectively added into SFMC at different ratios for formulating a suitable container medium for the growth of watermelon seedlings. A new container medium (SC medium) was formulated with SFMC and coconut fiber by volume at 1: 1 ratio. The SC medium was much more suitable for the growth of watermelon seedlings and showed strong suppression to the disease. The effects of SC medium on the pathogen and watermelon seedlings were further studied. Autoclaved (121℃, 15 lb, 30 min) and steamed (100℃, 30 min) treatments did not influence the suppression of SC medium to the pathogen and the disease. V-8 agar disks with the mycelium of the pathogen were dipped in either SC or BVB medium water-soluble extract for 26 hrs at 28℃. Oogonia and antheridia were greatly reduced in both water-soluble extracts; however zoospore differentiation was only inhibited in SC medium water-soluble extract compared to distilled water as a control. The pathogen invaded hypocotyls of watermelon seedlings grown in BVB medium and then spreaded rapidly. However, it was limited in hypocotyls of those grown in SC medium. Activities of phenylalanine ammonia lyase and peroxidase, which are involved in synthesis and polymerization of phenolic monomer and lignin, were significantly enhanced in hypocotyls of watermelon seedlings grown in SC medium compared to those grown in BVB medium as a control. The marked increment of lignin and ester-bounded phenolics incorporated into cell wall was observed in hypocotyls of watermelon seedlings grown in SC medium, but was not in BVB medium, by the spectrophotometer. Histochemical staining showed that lignin deposition was in epidermis of hypocotyl from watermelon seedlings grown in SC medium and resisted hyphal penetration of the pathogen, but was not one from BVB medium. These results indicated that the SC medium contained heat-stable abiotic inhibitors suppressing zoospore discharge of the pathogen and induced watermelon seedling roots to deposit phenolic compounds and lignin in hypocotyl cell wall expressing resistance to the disease.
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