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（2 ）可见的冻害症状： 叶子上的水浸状病斑； 皮层、芽点等坏死呈黑褐色；多肉组织常在冻 害后腐烂； 树体“破腹”。
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月季冻害症状 幼叶、芽点坏 死
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Winter injury 针叶树类冻害症状： 顶端幼针坏死
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Freeze damage on red pine. 红松冻害症状 Photograph courtesy G. Stanosz
African Violet -- Ring Spot (Water Spot) The necrotic areas on this Streptocarpus are due to cold water injury and are very similar to those on African Violet.
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精品资料
• 你怎么称呼老师？ • 如果老师最后没有总结一节课的重点的难点，你
是否会认为老师的教学方法需要改进？ • 你所经历的课堂，是讲座式还是讨论式？ • 教师的教鞭 • “不怕太阳晒，也不怕那风雨狂，只怕先生骂我
笨，没有学问无颜见爹娘 ……” • “太阳当空照，花儿对我笑，小鸟说早早早……”
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含羞草沤根
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树木在冬季易发生冻害的一个原因： 美国明尼苏达州冬天白天太阳直射树木，树木向阳一面 可比背阳面高25-300C，这足以引起向阳一侧树干中的冰 融化，如果太阳突然被遮，便会引起细胞内结冰导致伤 害。这种情况下，涂白的树干温度在向阳时可比未涂白 树干低300C，从而减小温差防止反复冻融的伤害 。
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第二章 植物病害的非侵染性病原
1ቤተ መጻሕፍቲ ባይዱ
Non-Infectious Diseases
Abiotic plant problems are those factors caused by other than living (biotic) agents. Abiotic factors include environmental conditions such as extreme temperatures, excess or lack of water, light, or nutrients, and abnormal conditions such as drought, flooding, and/or adverse cultural practices. Cultural practices may cause damage due to soil compaction, drifting of herbicides used to control weeds, and mechanical injury such as bark damaged by a lawnmower. Additionally, plants may have genetic abnormalities. All these factors, and many more, may create symptoms that appears to be caused by a plant disease. Inspection of the plant tissue is necessary in determining the cause of the plant damage.
