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A disease causing the decline of papaya (Carica papaya) plants was noticed in the Jordan Valley in 1982. The disease caused severe yellowing of the upper leaves and dieback of the apex. The disease was not transmissible mechanically and continued efforts to associate viruses and viroids have so far been unsuccessful. Epidemiological observations suggested that the disease is airborne and probably caused by a mollicute. In order to test this hypothesis, plots were covered by an insect-proof net and with white nets providing 15, 30 and 50% shade. The 30%, 50% and insect-proof nettings provided complete protection, and the 15% netting reduced disease incidence to <2%, compared with>37% in the uncovered control plot. Spraying plants at weekly intervals with a commercial whitewash solution was also found to be effective in reducing disease incidence. The advantages of using a range of netting field treatments as a simple means for obtaining information on the epidemiological nature of a new disease are described. 相似文献
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试验采用单因素随机区组设计,叶面喷施肥料的施肥方法,应用方差分析和多重比较分析试验数据,从而筛选出小菊最佳的营养元素配方。试验从不同叶面肥料在小菊上的筛选与应用研究的试验结果得到:小菊对肥料具有较强的选择性:三高灵的施用能够增加小菊的开花数量和鲜叶片叶绿素的含量;宝力丰的施用能提高小菊单株的干物重;OPAL的施用能延长小菊开花的花期。 相似文献
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The effect of separate chilling (5°C for 2 and 4 days) on the shoots and roots of two maize hybrid seedlings on the electric potential, the composition of fatty acids and the ATPase activity in the microsomes of non-chilled leaves and roots (20°C) was investigated. It has been found that the low temperatures induced on the non-chilled organs gave similar changes to organs exposed to a reduced temperature. The changes consisted of a parallel depolarization of leaf and root membranes and similarly a decrease in the ATPase activity as well as changes in the unsaturation of the membranes' fatty acids. The reduction of the acid content 18:2 was particularly significant, which in the leaf microsomes correlated with a drop in the ATPase activity.
The similarity between the reactions of the chilled and non-chilled parts of the plant gives evidence of a communication' between the organs which may facilitate a coordinated reaction of the entire organism to stress. The background for these phenomena could be die action potential of die chilled parts of seedlings which, in the non-chilled parts, might produce changes in the structure of biomembranes and in the activity of enzymes. 相似文献
The similarity between the reactions of the chilled and non-chilled parts of the plant gives evidence of a communication' between the organs which may facilitate a coordinated reaction of the entire organism to stress. The background for these phenomena could be die action potential of die chilled parts of seedlings which, in the non-chilled parts, might produce changes in the structure of biomembranes and in the activity of enzymes. 相似文献
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刘春明 《大连水产学院学报》1993,8(4):43-49
在构成基本型电阻电桥传感放大器的基础上给出了三种改善其性能的方法。1)补偿法。2)补偿加放大器改进综合法。3)负反馈法。通过实验证明了理论分析和实际效果是一致的,从而对电阻传感器在非电量检测中的广泛应用具有一定的实际意义。 相似文献
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According to the law for the current and voltage variance of the twophase system of the impedance matching balance transformer''s low equipment,we introduce the measuring method of real and reactive electric energy. A deep analysis for the error arising in 相似文献