Key message

This is the first report of the anti-oomycete activity of A. unedo leaves extract against Phytophthora cinnamomi. The extract was characterized by HPLC–MS and different chemotypes identified.

Abstract

Arbutus unedo L. is a small perennial Ericaceae tree well adapted to the environmental conditions of its Mediterranean distribution area. It produces a wide range of secondary metabolites with bioactive properties and applications for food, cosmetic and pharmaceutical industries. Due to the antifungal activity of some secondary metabolites they can play a key role in plant defense. In particular, arbutin and hydroquinone, two phenolic compounds typical of the Ericaceae species, might be especially important in plant defense against pathogens. Thus, in this work we (i) established a phenolic fingerprint of wild strawberry tree leaves, (ii) evaluated the effect of genotype and seasonal variation on phenolic metabolite composition, (iii) quantified arbutin and hydroquinone, and (iv) tested the antifungal effect of arbutin, hydroquinone and a methanol extract of A. unedo leaves against common strawberry tree pathogens. A total of 54 compounds were assigned by HPLC–PDA–ESI/MSⁿ, namely, gallic acid derivatives, hydrolysable and condensed tannins, flavonoids, arbutin, hydroquinone and their derivatives, and significant differences on relative abundance of the phenolic compounds between individuals were verified. Hydroquinone and its glucoside arbutin were quantified and its antifungal and anti-oomycete effect against A. unedo pathogens evaluated. Arbutin concentrations ranged from 0.69 ± 0.05 to 22.97 ± 0.76 mg g⁻¹ fresh weight of leaves. Hydroquinone was only detected in a few samples and its concentration ranged from 0.069 ± 0.004 to 0.604 ± 0.024 mg g⁻¹ fresh weight. Both arbutin and hydroquinone induced a reduction in growth of Glomerella cingulata and both compounds were highly effective against Phytophthora cinnamomi, with a reduction in growth close to 80% at the higher arbutin concentration tested. Microplate tests showed that a methanol extract of A. unedo leaves displayed an anti-oomycete activity with MIC (minimum inhibitory concentration) against P. cinnamomi at an arbutin equivalent concentration of 0.625 mg mL⁻¹, and was more active against P. cinnamomi than the arbutin standard (MIC = 12 mg mL⁻¹), which suggests that a synergic effect occurs in the presence of other metabolites existing in the extract. Moreover, extract containing an arbutin equivalent concentration of 2.5 mg mL⁻¹ was lethal for this pathogen. Arbutin, their derivatives and/or other secondary metabolites play an important role in A. unedo defense mechanisms against biotic stress, opening the way to biotechnological applications, namely, to use A. unedo leaf extracts as a natural phytosanitary agent. A genotype with the ability to produce high amounts of arbutin was also identified. The implications of these results on agroforestry management are discussed, as well as its relevance on plant phenotyping and selection for future breeding assays.

中文翻译：

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草莓树 (Arbutus unedo L.) 叶酚类化合物的季节性变化及对肉桂疫霉的抑制潜力

关键信息

这是 A. unedo 叶提取物对肉桂疫霉的抗卵菌活性的首次报告。提取物通过 HPLC-MS 进行表征，并确定了不同的化学型。

抽象的

杨梅L. 是一种多年生杜鹃花科小乔木，非常适应其地中海分布区的环境条件。它生产各种具有生物活性的次级代谢物，可用于食品、化妆品和制药行业。由于一些次生代谢物的抗真菌活性，它们可以在植物防御中发挥关键作用。特别是熊果苷和氢醌这两种杜鹃花科典型的酚类化合物，在植物防御病原体方面可能特别重要。因此，在这项工作中，我们 (i) 建立了野草莓树叶的酚指纹，(ii) 评估基因型和季节性变化对酚类代谢物组成的影响，(iii) 量化熊果苷和对苯二酚，以及 (iv) 测试抗真菌剂熊果苷、对苯二酚和甲醇提取物的作用A. unedo叶子对抗常见的草莓树病原体。通过 HPLC-PDA-ESI/MS ⁿ共鉴定出 54 种化合物，即没食子酸衍生物、可水解缩合单宁、黄酮类、熊果苷、对苯二酚及其衍生物，酚类化合物相对丰度在个体间存在显着差异。验证。对氢醌及其葡萄糖苷熊果苷进行了量化，并评估了其对A. unedo病原体的抗真菌和抗卵菌作用。熊果苷浓度范围为 0.69 ± 0.05 至 22.97 ± 0.76 mg g ^-1叶子鲜重。仅在少数样品中检测到对苯二酚，其浓度范围为 0.069 ± 0.004 至 0.604 ± 0.024 mg g ^-1鲜重。熊果苷和对苯二酚都诱导了Glomerella cingulata生长的减少，并且这两种化合物对肉桂疫霉非常有效，在测试的较高熊果苷浓度下生长减少接近 80%。微孔板试验表明，当熊果苷浓度为 0.625 mg mL ^{-1 时}，A. unedo叶的甲醇提取物显示出抗卵菌活性，MIC（最低抑制浓度）对P. cinnamomi 的抑制作用比对P. cinnamomi 的活性更高。熊果苷标准品（MIC = 12 mg mL ^-1)，这表明在提取物中存在其他代谢物的情况下会产生协同效应。此外，含有 2.5 mg mL ^-1熊果苷当量浓度的提取物对该病原体是致命的。熊果苷、它们的衍生物和/或其他次生代谢物在A. unedo抵御生物胁迫的防御机制中发挥重要作用，为生物技术应用开辟了道路，即使用A. unedo叶提取物作为天然植物检疫剂。还鉴定了具有产生大量熊果苷的能力的基因型。讨论了这些结果对农林业管理的影响，以及其与植物表型和未来育种试验选择的相关性。