• 作者： 杜金池; 程永雄; 鄭安秀;郭振欽; 何新奇
• 作者服務機構： 台灣省台南區農業改良場
• 中文摘要： 水稻紋桔病原菌(Rhizoctonia solani Kuhn AG-1)以菌核為主要感染源。菌核大部份漂浮於稻田水面，於插秧後十天，每 112.5c㎡菌核捕集網捕集菌核數，在溪口試驗田第一期作雙期作區為35.1，單期作區為26.9個，第二期作雙期作區為65.7個，單期作區為53.2個，發病率分別為35.5%，13.9%，28.3%及19.3%；斗六試驗田第一期作雙期作區為34.8個，單期作區為41.0個，第二期作雙期作區為21.3個，單期作區為4.6個，其發病率則分別為25.7%，37.35，23.1%及8.8%；漂浮於水面之病原菌菌核於插秧後日漸減少，一個月後便不易捕捉到。水稻紋枯病原菌菌核，部份漂向田埂內側成為無效侵染菌源，稻株上附著之菌核於插秧後15 ~30天開始侵染，菌核在菌株上附著及再產生之數目與紋枯病發病呈正相關。菌核在稻田水面之分佈受風向影響，溪口試驗田第一期作北風為主，東南及西南兩角菌核數較多。溫度與雨量影響紋枯病的發病情形，第一期作與發病率均呈正相關。水稻收獲後，菌核大部份殘留於稻樁上，稻樁上菌核數與落在土表菌核數比，溪口試驗地第一期作區為 7 : 1 ，埋入土中菌核為數極少，土表 5 公分以下便不易找到菌核。Rhizoctonia solani 在溪口、斗六兩試驗田中以 AG-2 菌?密度較高，分離百分率分別為74.3及65%，以分佈在土表 10 公分內之土層密度為主。
• 英文摘要： The majority of sclerotia of Rhizoctoniasolani of the anatomosis group AG-1 floated on irrigation water to serve as the primary inoculum of rice sheath blight. The highest sclerotial population was found 10 days after transplanting. In Si-Kou field trial, an aver- age of 35.1 and 26.9 sclerotia was collected from each 112．5cm2 surface area in the double cropping and the single cropping blocks during the 1st crop season, and an average of 65.7 and 53.2 sclerotia was collected during the 2nd crop season，respec- tively. The corresponding levels of disease incidence were 35.5, 13·9, 28·3 and 19·3%, respectively. In Tou-Lu field trial，therewere approximately 34.8 and 41.0 sclerotiacollected in the double and single croppingblocks, respectively, during the 1st cropseason as compared to 21.3 and 4.6 sclerotiacollected during the second crop season. Thecorresponding levels of disease incidence were25.6, 37.2, 23.0 and 8.8%, respectively.Eventually the number of floating sclerotiadecreased and they almost disappeared onemonth later. A few sclerotia which floated towardthe border of a paddy field were ineffectiveinocula. The effective ones attached to theleaf sheath of rice and infected the hosttissues at 15-30 days after transplanting.There was a positive correlation between thenumber of sclerotia on the sheath and thesheath blight incidence. The direction ofwind influenced the distribution of sclerotiaon the water surface. Since the northernmonsoon is usually stronger in the early stageof the 1st crop of rice, more sclerotia werecollected during this crop season from thesoutheast and southwest corners of the paddyfield in the Si-Kou field trial. The diseasewas also influenced by relative humidity andrain-fall, and there was a positive correlationbetween them. The sclerotia formed on diseased plantswere, however, partly fallen onto the soilafter rice harvesting. The ratio of thoseremaining on the stubble to those fallen ontothe soil was 7:1 in the 1st crop of rice inthe Si-Kou field trial. The sclerotia werescarce and difficult to find at a depth of 5cm in the soil. Of various anatomosis groups of R.solani, AG-2 was most frequently encounteredas 74.3 and 65.0% of plated sclerotia fromthe soil from the Si-Kou and Tou-Liu fieldtrials yielded AG-2 isolates, respectively.
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