Despite efforts of research to establish best nutrient management practices in HLB-affected citrus orchards, there are still doubts about the contribution of such strategies to minimizing losses caused by the disease in the citrus industry. We evaluated the effects of micronutrient (Zn, Mn, and/or Cu) supply and ‘Candidatus Liberibacter asiaticus’ (CLas) infection on physiological and growth traits of sweet orange trees (Citrus sinensis (L.) Osbeck)) to understand if enhanced micronutrient supply would improve the growth of plants infected with CLas and reduce bacterial infection, as well as the acquisition of CLas by adults and nymphs of Diaphorina citri, correlated with nutritional status of trees. Plants were either grafted with buds obtained from micrografted plants (healthy, −) or buds infected with CLas (diseased plants, +). Infected plants were exposed to one of the five nutrient treatments, applied to leaf and root: (i) nilZnMnCu+: not fertilized with Cu, Mn, and Zn; (ii) Zn+: fertilized with zinc sulfate (ZnSO4.H2O); (iii) Mn+: fertilized with manganese sulfate (MnSO4.H2O); (iv) Cu+: fertilized with copper hydroxide [Cu(OH)2]; and (v) ZnMnCu+: fertilized with all three micronutrients. Likewise, healthy plants were exposed to one of the two treatments as above: (i) nilZnMnCu− or (v) ZnMnCu−. We found that CLas impairs plant biomass production regardless of nutrient treatments, especially root growth, and increases specific leaf dry weight as disease progresses because of starch accumulation. Moreover, individual supply with Zn, Mn, or Cu can mitigate such deleterious effects of HLB on starch metabolism. HLB also changes nutrient concentrations in both leaves and sap extract, regardless of nutrient treatments, although treatments do not reduce the CLas titer in plants as determined by RT-qPCR. On the contrary, micronutrients applied in combination (ZnMnCu+) can reduce the acquisition of CLas by adults and especially nymphs of D. citri, likely reducing the disease infection in citrus orchards.

中文翻译：

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跟踪受 HLB 感染的树木中微量营养素供应的影响：植物反应和亚洲柑橘木虱对“Candidatus Liberibacter asiaticus”的获取

尽管研究努力在受 HLB 影响的柑橘园建立最佳养分管理实践，但仍然怀疑这些策略对最大限度地减少柑橘产业中该病害造成的损失的贡献。我们评估了微量营养素（Zn、Mn 和/或 Cu）供应和“Candidatus Liberibacter asiaticus”（CLas）感染对甜橙树（Citrus sinensis (L.) Osbeck）生理和生长特性的影响，以了解是否增强微量营养素的供应将改善受 CLas 感染的植物的生长并减少细菌感染，以及与树木营养状况相关的柑橘木虱成虫和若虫对 CLas 的获取。植物要么用从微嫁接植物（健康，-）获得的芽嫁接，要么用 CLas 感染的芽（患病植物，+）嫁接。将受感染的植物暴露于施用至叶和根的五种营养处理中的一种： (i) nilZnMnCu+：未用 Cu、Mn 和 Zn 施肥；(ii) Zn+：用硫酸锌 (ZnSO4.H2O) 施肥；(iii) Mn+：用硫酸锰 (MnSO4.H2O) 施肥；(iv) Cu+：用氢氧化铜 [Cu(OH)2] 施肥；(v) ZnMnCu+：添加了所有三种微量营养素。同样，健康植物暴露于上述两种处理之一：(i) nilZnMnCu- 或 (v) ZnMnCu-。我们发现无论营养处理如何，CLas 都会损害植物生物量的产生，尤其是根的生长，并且随着疾病的进展，由于淀粉积累，增加了比叶干重。此外，单独供应锌、锰或铜可以减轻 HLB 对淀粉代谢的这种有害影响。HLB 也会改变叶子和树液提取物中的营养浓度，无论营养处理如何，尽管处理不会降低由 RT-qPCR 确定的植物中的 CLas 滴度。相反，微量营养素组合使用（ZnMnCu+）可以减少成虫，尤其是柑橘若虫对CLas的获取，可能减少柑橘园的病害感染。