Morphogenetical studies on the stem pitting in citrus trees IV

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  • 柑橘樹における stem pitting の形成に関する研究 (第4報)
  • 柑橘樹におけるstem pittingの形成に関する研究-4-環境条件などが第2次木部の組織形成に及ぼす影響
  • カンキツジュ ニ オケル stem pitting ノ ケイセイ ニ カンスル ケンキュウ 4 カンキョウ ジョウケン ナド ガ ダイ2ジ モクブ ノ ソシキ ケイセイ ニ オヨボス エイキョウ
  • The effects of environmental factors on the tissue formation in the secondary xylem

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It has been clarified8, 9) that the abnormal tissue in secondary wood, related to stem pitting in citrus tree, was almostly formed in parenchymatous growth ring, but not in fibrous rings. And it was assumed that the formation of abnormal tissue (stem pitting phenomenon) might be dependent on cambial condition in a given season of a year.<br>So, the following experiments, using phytotron and green-house, were carried out with two year old trees of sweet lime (Citrus limettioides) in order to ascertain the effects of environmental factors on the formation of parenchymatous growth rings; in one, the effect of temperature on the trees grown under the constant high temperature (day and night: 30°C) and the alternate high temperature (day: 25-30°C and night: 15°C) during winter season (from the beginning of October till the end of April). And in another, the effect of day length on the trees grown under long day condition (13-15hr.) during the same winter, were examined. From the observation of the trees grown in natural conditions, it was revealed that the parenchymatous growth ring was formed in winter season while the fibrous growth ring was formed in summer season (from the beginning of May to the end of September). On the other hand, within all cases mentioned above, the formation of the parenchymatous growth rings was similar to that in the trees grown under natural condition in winter season except in the only case of the trees cultivated under the alternate high temperature. Under the alternate high temperature, during winter season, the differentiated secondary tissues were fibrous such as in summer season.<br>These observations provided that the thermoperiodicity was necessary for the differentiation of the fibrous growth rings in citrus tree wood.<br>Adding to the results mentioned above, the following facts were found; the formation of tissues in the secondary wood of two year old Buntan trees (Citrus grandis) which were operated mechanically (wounding to the basal part of main stem or cutting off the top of main stem) was similar to that of the tree grown under natural conditions, but in the case of cutting off all leaves or one part of lateral roots, the traumatic parenchymatous rings (similar to the terminal-type2)) were found in the secondary woods (Fig. 5. A and B, arrow).

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