Department of Plant Pathology, Citrus Research and Education Center, IFAS, University of Florida, Lake Alfred, FL, USA.
Chemistry Department, Faculty of Science and Technology, Al-Quds University, Jerusalem, Palestine.
Plant Signal Behav. 2020 May 3;15(5):1752447. doi: 10.1080/15592324.2020.1752447. Epub 2020 Apr 14.
Huanglongbing (HLB) is a highly destructive disease to the citrus industry in Florida caused by the bacterium, Liberibacter asiaticus(Las) and is transmitted by . 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 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 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 Las 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 Las bacteria. Understanding the mechanisms underpinning citrus tolerance to HLB will contribute to the development of commercially tolerant citrus cultivars.
黄龙病（HLB）是佛罗里达州柑橘产业的一种极具破坏性的疾病，由细菌韧皮部杆菌（Las）引起，并通过传播。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，分析了不同的柑橘品种和与有关的属的植物的总酚和类黄酮含量及其抗氧化能力。此外，还使用高效液相色谱-质谱联用（HPLC-MS）分析了七种柑橘属植物叶片中的次生代谢物。比色法测定表明，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不寻常的咔唑生物碱。耐受的物种含有高水平的酚类和类黄酮，并表现出高的抗氧化能力。我们的结果表明，高酚类和类黄酮叶含量与柑橘对 Las 细菌的耐受性增加有关。研究结果还表明，咖喱叶中具有强抗菌特性的咔唑生物碱含量较高，可能使其对 Las 细菌具有免疫力。了解柑橘对 HLB 的耐受性的机制将有助于开发商业上耐受的柑橘品种。
