• 作者： 楊盛行
• 作者服務機構： 國立臺灣大學農化系應用微生物研究室
• 中文摘要： 亞麻抑病土壤和導病土壤之物理、化學和生物性質上有些差異（表十四）：在酸鹼度上，抑病土壤呈微鹼性，而導病土壤則呈微酸性；在質地上，抑病土壤屬於黏土，而導病土壤則為粉質黏土；在陽離子交換能力上，抑病土壤因有機質含量較高，故 CEC 較導病土壤大；在田間保水力上，抑病土壤雖較導病土壤略低，但因導病土壤質地較黏重，因而其水分活性反而較抑病土壤低，在相同水分含量下，抑病土壞之水分活性皆較導病土壤高；在浸水條件下，抑病土壤之產氣量略比導病土壞低，但其乙烯產生量則比導病土壤高約二十倍；兩者雖在較嫌氣條件下（水分含量40%）時有最大產氣量，但其乙烯之最大產量則在較好氣條件下（水分含量20%），此與 Smith之結果不同；導病土壤之產氣時間雖比抑病土壤快，但其總產氣量卻遠比抑病土壤小；在產氣成分上，抑病土壤和導病土壤皆以 和 為主，而無顯著差異，但其量上則有別。 抑病土壤和導病土壤對水分含量之感受性不同（圖八），抑病土壤水分含量40%（水面活性1.0）時產氣量最高，其次為水分含量 35%，30%，80%，20%，50% 和 10%（水分活性分別為0.998，0.995，1.00，0.980，1.00 和 0.935）；而導病土壤亦以水分含量40%最大（水分活性0.998)，其次為50%，80%，35%，30%，20% 和 10%（水分活性分別為1.00，1.00，0.995，0.985，0.960和0.918）。水分活性可視為自由水之指標，其可由樣品之蒸氣壓與純水之蒸氣壓比值求得。當水分活性小於 0.6，所有微生物之生長受抑制，而水分活性小於0.9時，則一般微生物之生長幾乎受抑制。因而水分含量10%時（抑病土壤和導病土壤之水分活性分別為 0.935 和 0.918）部分土壤微生物之活性受抑制，所以氣體之產量大減。又土壤水分含量20%時，其水分活性在 0.96～0.98 之間，大部分之微生物活性不受影饗，因而其產氣量所受之影饗不顯著。雖然導病土壤之全氣體量比抑病土壤少，但其氣體色層分析譜很類似，只是量上有點差別。 所有由亞麻抑病土壤所分出對 Fusarium oxysporum f. sp. cubense race T 有拮抗活性之細菌，皆為G（一），桿菌，有莢膜，內生孢子，纖毛和周毛，除分離株 S-1c為較嚴格之嫌氣菌外，其餘十一個分離株皆為通性嫌氣菌，可產生多量之氣體，可能屬於 Clostridium 或 Bacillus 屬之細菌。其氣體成分有 和 ，其產氣量視菌株而異。 分離株S-7，5-d，S-1a，S-1b，S-1c 和國內分離株之混合、和國外分離株混合、和國內外十二個分離株混合，對鐮刀菌 Fusarium oxysporum f. sp. cubense race T 之生長皆有顯著之抑制力，而 F-17a，F-17b，F-17f 則較弱，F-17，F-17d，F-17g 和 F-17h 之抑制力不明顯。又分離株對濂刀菌菌絲生長之抑制力與其氣體總產量約成比例，但與乙烯之產生量之間係不明顯（表十六）。另 5% 之 氣體對鐮刀菌厚壁孢子之發芽力亦有明顯之抑制作用。 由以上之結果推論抑病土壞之抑病因子，可能與土壞水分活性和菌體代謝產物（包括揮發性物質）有關，而不是單獨由某一因子所造成的。
• 英文摘要： There were some differences in the physical,chemical and biological properties between theflax-suppressive soil and conducive soil (Table14): The acidity of the suppressive soil wasslightly alkaline while the conducive soil wasslightly acidic; The texture of the former wasa sort of clay while the latter was silty clay;The cation exchange capacity and the organicmatter content of the former were higher thanthose of the latter; The water holding capacityof the suppressive soil was lower than that ofconducive soil, but the latter was more sticky.Therefore under the same moisture content, thewater activity of suppressive soil was largerthan conducive soil. It means that under thesame moisture content, the available water ofsuppressive soil was more than that of conducivesoil; In submerged condition, gas production ofthe former was lower than the latter, but ethy-lene concentration in the gas was vice verses;Both of them had the maximum gas productionunder more moisture (40% water content) whichwas probable more anaerobic, but the maximumethylene production was under less moisture(20% water content) which was probable moreaerobic. This result was somewhat differentfrom the observation of Dr. Smith, who postu-lated that ethylene production was due to theanaerobic condition. The effect of water content on the gasproduction of suppressive soil and conducivesoil was somewhat different (Fig. 8): In sup-pressive soil, the maximum gas production was at40% water content (a,a＝1.00), then decreased inthe follow order: 35%, 30%, 80%, 20%, 50%and 10% ( ＝0.998, 0.995, 1.00, 0.980, 1.00 and0.935); while in conducive soil, the maximumgas production was also at 40%, but decreasedin the follow order: 50%, 80%, 35%, 30%,20% and 10% ( ＝1.00, 1.00, 0.995, 0.985, 0.960and 0.918). Water activity is an index ofthe freedom of water which can be measured bythe ratio of the vapor pressure of sample to thevapor pressure of pure water. As the below0.60, the growth of microorganisms is inhibited,while the less than 0.90, the growth ofgeneral bacteria is almost inhibited. Therefore,the activity of soil microbes was partially inbi-bited in 10% water content ( is only 0.935and 0.918 in suppressive soil and conducive soilrespectively), so the gas production was decreasedvery sharply. However, 20% water content ofsoil, the is around 0.96-0.98, the activity ofmost microorganisms is not inhibited, so theinhibition of gas production was not significant.Although the total gas volume of the conducivesoil was less than suppressive soil, but the gaschromatogram patterns of those gases were verysimilar qualitative, and it was somewhat differentquantitatively. All the bacteria isolated from the flax-sup-pressive soil with regard to the antagonisticactivity against Fusarium oxysporum f, sp. cubenserace T were rod, gram negative, with capsule,endospore, pili, polar flagella and gas production.Except of the isolate, S-lc, was strict anaerobic,all of them were facultative anaerobes. Theymay be clostridia and/or bacilli. The major gascomposition was and , alth-ough each isolate showed different patterns ofgas production. Each of the isolates, S-7, 5-d, S-1a, S-1b,and S-1c, and three combinations of mixedcultures (see the text) had a significant inhibitionon the growth of F. oxysporum f. sp. cubenserace T. The isolates F-17a, F-17b and F-17fhad a weak inhibition, while F-17, F-17d, F-17gand F-17h had no inhibition. The inhibitoryeffect of the isolates on the growth of F. oxy-sporum was approximately parallel to the totalgas production, but the relationship betweenethylene formation and inhibitory effect was notso definite. 50% of pure in air, which maybe not possible in soils, had also a significantinhibition of the germination of chlamydosporeof F. oxysporum, while 2% of ethylene in gasindicated 40% inhibition. From the results mentioned above, it isdefinite that the suppressive effect of flax-sup-pressive soil may be due to the water activityof the soils which effects the microbial activi-ties of soils.
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