Calonectria leaf spot, caused by Calonectria pteridis, is a serious problem in Eucalyptus crops in both nursery and the field. Under ideal conditions, the disease can cause severe defoliation. It is known that calcium and potassium are directly related to the plant's resistance to pathogens. Thus, the knowledge of how a balanced fertilization of Ca and K interferes in the distribution of these nutrients at the infection site would contribute to elucidate the resistance of the plant related to its nutrition. This study investigated the effect of calcium and potassium fertilizer application on the content and distribution of these nutrients in the symptomatic leaf area, transition zone and asymptomatic leaf area over time. Eucalyptus seedlings were grown in nutrient solution under different Ca and K treatments (6 mmol/L K + 4 mmol/L Ca, 6 mmol/L K + 8 mmol/L Ca and 9 mmol/L K + 12 mmol/L Ca) and inoculated with C. pteridis. Leaves were removed at 24, 48 and 72 hr after inoculation (hai) and evaluated by X‐ray microanalysis. The highest calcium content among the different leaf areas was observed in the symptomatic area, and the levels in this area increased over time, with the highest mean value observed at 72 hai in the 6K + 8Ca treatment. In the other treatments, the mean calcium content peaked at 48 hai and then decreased. A similar pattern in asymptomatic tissue was observed for potassium in the 6K + 8Ca treatment. Fertilization with calcium and potassium directly affected the demand and availability of nutrients at different times during infection. These results demonstrate that plant defence responses and their continuity over time during infection rely on balanced calcium and potassium fertilization because these nutrients are directly involved in plant resistance to the pathogen.

中文翻译：

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桉树叶中钙、钾的分布及含量

Calonectria pteridis 引起的 Calonectria 叶斑病是桉树苗圃和田间作物的严重问题。在理想条件下，该病害可导致严重的落叶。众所周知，钙和钾与植物对病原体的抵抗力直接相关。因此，了解钙和钾的平衡施肥如何干扰这些营养物质在感染部位的分布，将有助于阐明植物与其营养相关的抗性。本研究调查了随着时间的推移，钙和钾肥的施用对有症状叶区、过渡区和无症状叶区中这些营养素的含量和分布的影响。桉树幼苗在不同Ca和K处理（6 mmol/L K + 4 mmol/L Ca，6 mmol/L K + 8 mmol/L Ca 和 9 mmol/L K + 12 mmol/L Ca) 并接种 C. pteridis。在接种后 24、48 和 72 小时去除叶子（hai）并通过 X 射线微量分析进行评估。在有症状的区域观察到不同叶区域中钙含量最高，并且该区域的水平随着时间的推移而增加，在6K + 8Ca处理中观察到的最高平均值在72海。在其他处理中，平均钙含量在 48 海时达到峰值，然后下降。在 6K + 8Ca 治疗中观察到钾在无症状组织中的相似模式。钙和钾的施肥直接影响感染期间不同时间的营养需求和可用性。