イモチ病菌の分生胞子の発芽による附着器の形成とその病理学的意義について

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  • イモチ病菌の分生胞子の発芽による附着器の形成とその病理学的意義について(農学部門)
  • イモチ ビョウキン ノ ブンセイ ホウシ ノ ハツガ ニ ヨル フチャクキ ノ ケイセイ ト ソノ ビョウリガクテキ イギ ニ ツイテ
  • On the Appressorium Formation of Conidia of Rice Blast Fungus and Its Pathological Significance (Agriculture)

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1. The formation of appressorium, though imperfect in shape and scanty in number, was observed when the conidia of rice blast fungus, Piricularia oryzae, were allowed to germinate on CZAPEK medium containing 6% agar for 24 hours. 2. On the matured leaves of rice varieties "Late Shinriki" and "Tetep" there was more formation of appressorium on the former variety than on the latter. This was considered grade of varietal resistance to blast fungus. On such matured leaves in the peak tillering stage, there was a rising tendency in the percentage of appressorium formation even after 30 hours. While on seedling leaves of "Norin No. 1" variety, the percentage of appressorium formed nearly coincided with that on slide glasses, which was greater than that on matured leaves. 3. The optimum, minimum and maximum temperatures for the formation of appressorium (over 90% of germinated spores to form appressorium) was 24-28℃, 12-14.5℃ and near 36℃, respectively. The range of optimum temperature for spore germination is moderately wider than that for appressorium formation. Spore germination after 8 hours and appressorium formation after 18 hours both showed high percentages of over 90%. 4. The appressorium of the rice blast fungus showed a striking resistability to fungicides Liogen (organic mercurial) and Sankyo Bordeaux. The limit in the concentration for the appressorium to survive Liogen was immersion in 1/400 dilution for a period of 50 minutes (twice the concentration recommended for general use), but that for Sankyo Bordeaux it was much greater as the fungus was still alive after 60 minutes in 1/150 dilution (twice the recommended concentration for general practical use). 5. The thermal tolerance of appressorium and mycelium of rice blast fungus at 58-60℃ was less in wet heat than in dry heat, namely, its limits were 10 minutes for the former and 60 minutes for the latter. 6. The size of appressorium of rice blast fungus formed on the glass surface measured 7.8-10.7×8.6-12.3μ, and there was a positive correlation (correlation coefficient : 0.684) between the length and the width of appressorium. Within a favorable temperature range for appressorium formation, the size of appressorium of blast fungus was larger at 26℃, and there was a significant difference between size of appressorium and cultural temperature. Between size of spore and appressorium formed, there was a lower positive correlation (correlation coefficient : 0.158).

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