行政院農業委員會台南區農業改良場  研究彙報第15號

水稻紋枯病原菌之生態及生物防治研究

杜金池 張義璋

摘  要

水稻紋枯病(Rhizoctonia solani Küuhn AG1)以菌核為主要感染源。菌核大部份漂浮於稻田水面,以整田至插秧期間菌核量最多,每個112.5cm2菌核捕集網10日內菌核收集量在屏東麟洛試驗田第一期作為18.7個,第二期作為52.7個,在台中大安試驗田第一期作為49.4個,第二期作為31個,插秧後田間菌核捕集數逐日遞減,一個月後就不易捕捉到菌核。各期作稻田紋枯病原菌每公頃菌核捕集總數量為屏東麟洛試驗田第一期作4.7×107個,發病率14.1%,第二期作1.02×108個,發病率23.2%,台中大安試驗田第一期作8.3×107個,發病率45.2%,第二期作4.6×107,發病率53.4%。第一期作初期西北季風較強,稻田東南角水面漂浮之菌核最多,並呈極顯著之差異。因此,菌核在稻田水面之分佈,風向及風速影響頗大,灌溉水次之。

稻椿為病原菌菌核主要滋生處所,其產生受到空氣相對溼度及溫度之影響頗大。RH88%之濕度下,20∼(24)∼28℃最易產生菌核,24℃時平均每一罹病稻桿可產生11個菌核。在PDA培養基上,12∼(16)∼24℃均易產生菌核。32℃時病株上可產生菌核,但在PDA上則產生大量氣生菌絲。台中大安試驗田在第一期作(栽植台南5號)收穫時調查水稻紋枯病株上菌核與掉落土表面之比例約為8:1,收穫後罹病稻椿中平均尚發現有28.6個菌核,屏東麟洛則平均為每稻椿9.7個菌核。屏東試驗田於第二期水稻收穫後約1月發現平均每一稻椿有46.8個菌核,稻椿外土壤菌核則甚為稀少。

菌核在積水狀況下,埋入土中2cm以下,其殘存力約8個月,土表面菌核可存活2年以上。

水稻紋枯病原菌寄主範圍甚廣,如馬鈴薯、大豆、豌豆、玉米、高粱與亞麻等冬季塈@及田間雜草均可被危害,病株也會產生菌核,尤以稗草(Echinochlora crus-galli)為甚。

氣溫28℃時最適紋枯病之發生,24℃時最適宜病斑擴展,12℃時接種7天並未見發病。相對溫度(RH)81∼92%最適宜紋枯病發病,RH95%以上對紋枯病稍有限制,低於RH65%時則不利紋枯病發生。

水稻品種對紋枯病均為感病。在自然環境下,以人工接種5個供試品種,雖罹病率無差異,但病斑之擴展則因品種而有程度上之差異。

Trichoderma harzianumRhizoctonia solani 具有強寄生力,但抗生及競生能力較差。Trichoderma virideTrichoderma konigii有強的抗生力,但寄生力較差。


Ecology of Rice Sheath Blight Pathogen, Rhizoctonia solani Kuhn AG1, with References on the Biological Control with Trichoderma spp.

C. C. Tu and Y. C. Chang

Summary

        The majority of sclerotia of Rhizoctonia solani AG 1 floated on the irrigation water to serve as the primary inoculum of the rice sheath blight.  The highest population was found during the period from land preparation to transplanting of seedlings.  There were approximately 18.7 and 52.7 sclerotia collected from each 112 cm2 area of water surface in the 1st and 2nd crop or rice, respectively, in Pin-tung trial during this period, while approximately 49.4 and 31 sclerotia in the 1st and 2nd crop of rice, respectively, in Tai-chung trial.  Eventually the number of floating sclerotia decreased and almost disappeared one month later.  The total sclerotia floating on the irrigation water was estimated 4.7 × 107 sclerotia/ha at the 1st crop of rice with 14.1% of the disease, or 1.02 × 108 sclerotia/ha at the 2nd crop of rice with 23.2% of the disease in the Pin-tung trial, while 8.3 × 107 sclerotia/ha at the 1st crop of rice with 45.2% of the disease, or 4.6 × 107 sclerotia/ha at the 2nd crop of rice with 53.4% of the disease in the Tai-chung trial.

        Since the northwest monsoon is usually stronger in the early stage of the 1st crop of rice, more sclerotia were collected from the southeast corner of the paddy fields observed.  It was thus concluded that the distribution of sclerotia of R. solani AG 1 on the water surface on the paddy fields was greatly influenced by the direction and velocity of wind.  The running direction of irrigation water played as the role of second importance.

        The optimum condition for sclerotial formation on diseased stalk was found at 20-(24)-28℃ with a relative humidity (RH) of 88%; approximately 11 sclerotia/stalk was observed at 24℃.  The fungus produced more sclerotia at 12-(16)-24℃ on potato-dextrose agar medium.  Few sclerotia formed on the diseased plants at 32℃, but none was observed on potato-dextrose agar medium.

        The sclerotia formed on the diseased plants were, however, partly dropped onto the soil in the field after harvest.  The ratio between those remaining on the stubble and dropping onto the soil was found to be 8:1 in Ta-an, Tai-chung.  It was found that about 28.6 sclerotia on each stabble after the harvest of the 1st crop of rice and about 16.8 sclerotia per stabble after the harvest of the 2nd crop of rice.

        The longevity of sclerotia was about 8 months in soil under the submerged condition.  However, they survived longer than 2 years if they were placed on the soil surface instead of in the soil.

        The pathogen was proved with a very wide host range.  Winter crops of paddy field such as potato, soybean, pea, corn, sorghum, flax and numerous paddy weeds were included.  Sclerotial formation was also found from some diseased plants, especially those of Echinochlora crus-galli.

        The disease was the most prevalent at 28℃.  The spot expanded rapidly at 24℃.  No disease was observed at 12℃ in 7 days after inoculation.  Relative humidity 81~92% was the best condition for the disease development.  Higher than RH 95% or lower than RH 65% was not suitable.

        All rice varieties tested were susceptible to the disease.  There was no difference on the disease incidence among 5 varieties tested, but lesion expansion was different with variety concerned.

        Trichoderma harzianum was antagonistic to R. solani AG 1 with the mechanism of parasitism rather than antibiosis and competition.  T. viride and T. konigii, the other hand, showed stronger antibiotic effect than parasitic effect to the pathogen.  Application of T. viride to control both winter crop (flax) damping off caused by R. solani AG 1 and rice sheath blight was effective but was not statistically significant (p=5%).  More studies on the application technique are needed before the practical value of Trichoderma spp. As a bio-control agent to R. solani AG 1 can be determined.

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