Abstract The aim of the study was to examine the responses of mature ‘Red Jonaprince’ apple (Malus domestica Borkh.) trees/M.26 to molybdenum (Mo) sprays. The experiment was conducted in Central Poland in 2017-2018 at high-density orchard growing on strongly acidified coarse-textured soil with low Mo availability. Trees were sprayed with Mo in the form of sodium molybdate before bloom (at pink bud), at bloom (when 5-20% of flowers were open) or after bloom (14 days after petal fall). In each spray, the Mo rate was 286 g ha-1. Trees that were not treated with Mo served as the control. Except for manganese (Mn), the concentrations of the essential macro- and micronutrients in the summer leaves of the control trees were within optimum/sufficient ranges. The summer leaf Mn concentrations were high but not toxic. Prebloom and bloom Mo sprays increased the activity of nitrate reductase (NR) and SPAD chlorophylometer values for leaves at 21 days after full bloom (DAFB), Mo concentrations in flowers and seeds, the number of seeds in an apple, fruit Ca concentration (on average by 23% for both Mo spray treatments), and the Streif index values of the fruit at harvest. The postbloom Mo spray increased the summer leaf concentrations of nitrogen, magnesium, iron and Mo, and the NR activity and SPAD values of leaves at 21 DAFB and at harvest. No Mo spray affected tree vigour, fruit set and yield, mean fruit weight, skin russeting and blushing, and the soluble solids concentration and flesh firmness of apples at harvest. It is concluded that when the apple flower Mo concentration, at least in triploid varieties, is as low as 1.5 mg kg-1 DW, a prebloom or bloom Mo spray is recommended to improve Ca-related apple quality.

中文翻译：

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喷钼对‘红乔纳普林斯’苹果树生长、产量和果实品质的影响

摘要 本研究的目的是检查成熟的“红乔纳普林斯”苹果（Malusdomestica Borkh.）树/M.26 对钼 (Mo) 喷剂的反应。该试验于 2017 年至 2018 年在波兰中部在高密度果园中进行，该果园生长在钼含量低的强酸化粗糙土壤上。树木在开花前（粉红色芽）、开花时（5-20​​% 的花朵开放时）或开花后（花瓣落下后 14 天）喷洒钼酸钠形式的钼。在每次喷雾中，钼含量为 286 g ha-1。未用 Mo 处理的树木作为对照。除锰 (Mn) 外，对照树木夏季叶片中必需常量和微量营养素的浓度均在最佳/充足范围内。夏季叶片锰浓度高但无毒。开花前和开花前喷施钼提高了盛开后 21 天叶片的硝酸还原酶 (NR) 和 SPAD 叶绿素计值 (DAFB)、花朵和种子中的钼浓度、苹果中的种子数、果实中的钙浓度（上Mo 喷雾处理平均增加 23%），以及收获时果实的 Streif 指数值。花后钼喷雾增加了夏季叶片的氮、镁、铁和钼浓度，以及 21 DAFB 和收获时叶片的 NR 活性和 SPAD 值。无钼喷剂影响苹果在收获时的树势、坐果和产量、平均单果重、皮肤赤褐色和发红，以及可溶性固形物浓度和果肉硬度。得出的结论是，当苹果花 Mo 浓度（至少在三倍体品种中）低至 1.5 mg kg-1 DW 时，