Aanatomical observation of the development of freezing injury in orchardgrass crown

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  • オーチャードグラス冠部における凍結害の発生経過の形態観察
  • オーチャードグラス カンブ ニ オケル トウケツ ガイ ノ ハッセイ ケイカ

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The process of the freezing injury in the crown of the seedlings of orchardgrass (cv. Kitamidori) was studied using by paraffin sections made at thawing and by observing regrowth of seedlings after two freezing treatments ; 1. Freezing at -3℃, -6℃, -9℃ and -14℃ for 16 hrs (Short time freezing), 2. Freezing at -3℃ and -6℃ with several durations up to 12 weeks (Long time freezing). In short time freezing, the percentage of survival plants, their fresh weight and their plant height decreased with the decreasing of temperature. The regrowth of the main shoot was less than that of tillers. The damage of the organs and tissues both of the main shoot and the tillers increased with the decreasing of temperature. The damage was heavier younger leaves (Y) followed by transitional region (T), shoot apex (S), basal part of the leaf sheath (B), lateral bud (L) and root primodia (R). The main shoot was injured more than the tillers. In long time freezing at -3℃, the number of leaves which developed from the main shoot started to decrease at 2 weeks, and the killing of plants began at 6 weeks. The damage of the organs and the tisses both of the main shoots and the tillers was increased as the freezing was prolonged. The main shoots were injured more than the tillers. The decreasing order of the degree of damage was Y≧S>L>B>T≧R. In long time freezing at -6℃, almost all the plants died at 2 weeks. The main shoots of ten cultivars which were differed in frost hardiness were injured more than their tillers during the short time freezing of -3℃, -10℃ and -12℃. Their shoot apices were injured more than their lateral buds. The younger leaves and the shoot apices of larger tillers were more damaged than those of the smaller tillers (the primary tiller from the larger tiller) within a plant which were collected from several pastures in Obihiro at the end of snow cover. These results indicated the importance of freezing injury which causes the death of younger leaves and shoot apices of vigorous tillers and finally decreases the number of ears at first cut in every year in the pastures of soil freezing area, eastern Hokkaido.

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