ABSTRACT Huanglongbing (HLB) is a highly destructive disease to the citrus industry in Florida caused by the bacterium, Candidatus Liberibacter asiaticus(CLas) and is transmitted by Diaphorina citri. It is hypothesized that plants with high phenolic contents show higher tolerance to certain plant pathogens. In this regard, different citrus varieties and plants of genera related to Citrus were analyzed for their total phenolic and flavonoids contents, and their antioxidant capacities. In addition, the secondary metabolites in the leaves of seven citrus species were analyzed using high performance liquid chromatography-mass spectrometry (HPLC-MS). Colorimetric assays showed that curry leaf contained the highest total phenolic content and free radical scavenging activity (DPPH). Curry leaf also contained high concentrations of an unusual class of carbazole alkaloids. Tolerant Citrus species contained high levels of phenolics and flavonoids and showed high antioxidant capacities. Our results suggest that high phenolic and flavonoid leaf contents correlate with increased citrus tolerance to CLas bacterium. The results also suggest that the high level of carbazole alkaloids, known for their strong antimicrobial properties in curry leaf, could make it immune to the CLas bacteria. Understanding the mechanisms underpinning citrus tolerance to HLB will contribute to the development of commercially tolerant citrus cultivars.

中文翻译：

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不同耐黄龙病柑橘类植物酚类、黄酮类物质及抗氧化能力

摘要 黄龙病（HLB）是一种对佛罗里达柑橘产业具有高度破坏性的病害，由细菌念珠菌（Candidatus Liberibacter asiaticus，CLas）引起，由柑橘木虱传播。据推测，酚类含量高的植物对某些植物病原体表现出更高的耐受性。在这方面，分析了与柑橘相关的不同柑橘品种和属植物的总酚类和类黄酮含量，以及它们的抗氧化能力。此外，使用高效液相色谱-质谱法 (HPLC-MS) 分析了七种柑橘类植物叶片中的次生代谢物。比色分析表明，咖喱叶含有最高的总酚含量和自由基清除活性（DPPH）。咖喱叶还含有高浓度的一类不寻常的咔唑生物碱。耐受性柑橘类植物含有高水平的酚类和黄酮类化合物，并显示出高抗氧化能力。我们的结果表明，高酚类和类黄酮叶含量与柑橘对 CLas 细菌的耐受性增加有关。结果还表明，咖喱叶中高含量的咔唑生物碱以其强大的抗菌特性而闻名，可以使其对 CLas 细菌免疫。了解支持柑橘对 HLB 耐受的机制将有助于开发具有商业耐受性的柑橘品种。我们的结果表明，高酚类和类黄酮叶含量与柑橘对 CLas 细菌的耐受性增加有关。结果还表明，咖喱叶中高含量的咔唑生物碱以其强大的抗菌特性而闻名，可以使其对 CLas 细菌免疫。了解支持柑橘对 HLB 耐受的机制将有助于开发具有商业耐受性的柑橘品种。我们的结果表明，高酚类和类黄酮叶含量与柑橘对 CLas 细菌的耐受性增加有关。结果还表明，咖喱叶中高含量的咔唑生物碱以其强大的抗菌特性而闻名，可以使其对 CLas 细菌免疫。了解支持柑橘对 HLB 耐受的机制将有助于开发具有商业耐受性的柑橘品种。