臺灣亞麻萎凋病之抑病土壤

Abstract

調查本省秀水鄉和福興鄉一帶亞麻萎凋病猖獗發生地區6處麻田發現5處是導病土壤，僅1處為抑病土壤。抑病土壤經人工接種亞麻萎凋病菌（Fusarium oxysporum f. sp. lini）大型分生胞子懸浮波或亞麻罹病株莖碎片被栽植亞麻時會發生萎凋病，但發病率不因連作而增加，却反而減少。抑病土壤內萎凋病病原菌體增加速度緩慢，連作亞麻後侵染源密度增加8%，而導病土壤則增加23-66%。厚膜胞子在抑病土壤內發芽率最高達44%，發芽管平均長度為192µm，細菌往往聚集在發芽管和厚膜胞子之周圍而發生溶菌情形。反之，厚模胞子在導病土壤內發芽率可達63%，發芽管平均長度大於250µm，並無細菌聚集發生溶菌情形。抑病土壤是黏土，導病土壤都是坋質黏土。 三種不同處女土經人工接種亞麻萎凋病病原菌援，以亞麻罹病率為指示，發現砂岩屬於”導病土壤”，紅泥壤屬於”中間型”或”中等抑病土壤”，而泥板岩最具”抑病”特性。 Flax has long been recognized as one of the important economic crops and as a main source of fiber and painting oil in Taiwan. Unfortunately this crop has been seriously attacked by Fusarium oxysporum f. sp. lini and largely limited its production. A survey showed in 1974 that 505 out of 4,600 hectars of flax were partially attacked and 120 hectars were completely destroyed by the pathogen. In the area where the disease was prevalent, occasionally a few flax field was found to be completely free from the disease, while in its vicinity the flax was severely attacked. According to an investigation on soils from both healthy and diseased fields through a pot test by(1) inoculating the soil with F. oxysorum f. sp. lini,(2)estimating the pathogen prior to and thereafter the experiment, and (3) observing the chiarnydospore germination and germ tube length, it is concluded that there are soils with different properties; one is conducive and the other suppressive to the wilt. In the former the disease becomes serious quickly, the pathogen propagules increase repidly, and chiamydospore germinate and normally. In the latter the disease decreases gradually, the pathogen propagules multiply slowly, andchlamydospores are rather difficult to germinate, and even if they germinate the germ tubes are short and always surrounded by bacteria resulting the lysis of germ tubes. Among various virgin soils tested, a sandy soil (sand stone as parent material) is rather wilt-conducive, whereas a clayey soil (shale as parent material) shows strongly wilt-suppressive. A red clay (parent material unknown) is intermediate or moderately wilt-suppressive. Sandy soil amended with cornmeal could not reduce the disease if macroconidium-.suspension was inoculated, but 11% of disease reduction was obtained if diseased flax stem was used instead. The fact might indicate that the sandy soil lacks of antagonistic bacteria and the disease reduction might be by virtue of the bacteria carried from the flax residues. The other two soils, especially red clay, showed 15?5 of disease reduction after the amendment of cornmeal into those of artificially infested with macroconidium-suspension. This result indicates that some resident antagonists have been already in these two virgin soils. These facts convinced us that antagonists might play a significant role in the suppressive soil.