• 作者： 梁文進
• 作者服務機構： 臺灣省立屏東農業專科學校
• 中文摘要： 氣象條件為影響稻熱病流行之重要因子，尤其對於病菌感染前各種行為之發展更為密切。自
  新鮮病斑釋放的成熟胞子，接種於新生稻葉上，以更合乎自然條件而來檢討溫度及水滴對胞子發
  芽、附著器形成及侵入等感染前行為的影響。
  稻熱病胞子發芽、附著器形成及侵入，必須在有水滴的存在方能進行。此等行為活動的適宜
  溫度為16　～28　C，但胞子發芽之溫度範圍更廣，甚至可降低到12　C及提高到36　C。最適溫度
  為24　C，胞子發芽始於浸水後2小時，附?器形成則於浸水後3小時，而侵入則於浸水後6小
  時，且浸水時間愈長，對一切行為愈有利。但若浸水時間短於2小時，胞子經過乾燥1小時以上
  ，即大大降低發芽率；浸水2小時以上，而短於侵入寄主所需時問，則胞子因乾燥而喪失其活性
  。這說明田間稻熱病菌胞子在早晨露水消失前6小時內所釋放的，可能因露水消失後浸水時間不
  ?，不足以完成其侵入即受乾燥而喪失其惑染能力；反之，晝間至凌晨左右所釋放之胞子，往往
  可獲得長時間露水之浸潤而達成有效的感染。
  稻熱病流行之先決氣象條件為溫度，它決定了流行的地區及季節。但於適宜稻熱病發生的溫
  度期間，露水和雨水的多少及彼等存留於葉片上時問的長短，便成為主宰該時期稻熱病流行程度
  的主因。
  r
• 英文摘要： Meteorological factors have long beenknown to influence the outbreak of the riceblast disease significantly, especially their in-fluence on preinfection behaviors of the blastfungus, Pyricularia oryzae, are worthy of atten-tion. Mature conidia of P. oryzae released fromyounger lesions are harvested and inoculated onthe surfaces of detached leaves of rice plant.This mode of inoculation method is used as abasic tool in this paper for studying the effectsof temperture and water droplets on the beha-viors of spore germination, appressorium for-mation and penetration into the leaf tissues. Experimental results reveal that water drop-lets are necessary for spore germination, appres-sorium formation and penetration of the blastfungus into leaf tissues. The suitable tempera-ture range for spore germination is from 16 to32 C, however, for appressorium formation andfor penetration, much narrower temperature ran-ge of 16 to 28 C is observed. Under optimumtemperature 24 C, the hours required for conidiabeginning to germinate, for appressorium toform, and for invasion into leaf cells are 2, 3and 6 respectively after the conidia are sus-pended in the water. The longer. the waterdroplets exist on leaf surfaces, the more pene-tration is obtained. The wetted conidia of P. oryzae are harmedby desiccation. If the conidia are previouslywetted in water for shorter than 2 hours, thenbeing followed by desiceatting in air for evenonly one hour, germination of the conidiawill decrease greatly. However, the desiccationwill also cause conidia to lose their viability ifthe conidia suspended in water lasts for longerthan 2 hours but shorter than 6 hours whichis the time required for penetration. Penetration is achieved by formation ofpenetrating hyphae from appressoria which pe-netrate into host cells directly. After penetra-tion, the cytoplasm of the appressroial cell mi-grates to the penetrating hyphae in the hostplant. This can be identified by staining theappressoria with cotton blue, appressoria withoutcytoplasm are not stained while appressoriawith cytoplasm are deeply stained. In brief, the prevalence of rice blast diseaseis dependent first on the temperature which de-termines where and when the disease will out-break, thereafter, the duration and amounts ofdew and rainfall become key factors of influenc-ing the disease severity.
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