Blackspot, caused by , is a significant postharvest disease in pitaya. Currently, there are limited effective fungicides to manage this disease. This study aimed to evaluate the antifungal activity of citral against the blackspot pathogen and to determine the protective effect of citral on pitaya. Our results demonstrated that citral effectively curtailed the mycelial growth and spore germination of , with a minimum inhibitory concentration (MIC) of 0.6 μL/mL. Observations under a light microscope revealed that citral-treated hyphae displayed characteristics such as sparseness, roughness, twisting, shriveling, and irregular internode separation, along with prominent vacuolation. Propidium iodide and 2,7-Dichlorodi-hydrofluorescein diacetate staining results revealed that the mycelia from the MIC citral-treated group emitted robust fluorescence, with the average fluorescence intensities being 4.03 and 8.09 times higher than the control group, respectively. Furthermore, citral treatment resulted in a decline in the lipid content and dry weight of the hyphae, increased nucleic acid and protein leakage, enhanced exosporial conductivity, and augmented superoxide dismutase (SOD) and catalase (CAT) enzyme activities. Additionally, it fostered the accumulation of hydrogen peroxide (HO) and malondialdehyde (MDA). Fruit damage inoculation assays indicated that an appropriate concentration of citral (1/2 MIC, MIC) could notably diminish the fruit spot diameter expansion. Thus, citral shows promise as a potential alternative fungicide for managing postharvest black rot in pitaya.

中文翻译：

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柠檬醛对火龙果黑腐病的抑制作用及作用机制

黑斑病是由 引起的，是火龙果采后的一种重要病害。目前，用于控制这种疾病的有效杀菌剂有限。本研究旨在评估柠檬醛对黑斑病病原体的抗真菌活性，并确定柠檬醛对火龙果的保护作用。我们的结果表明，柠檬醛有效抑制了菌丝体生长和孢子萌发，最低抑菌浓度 (MIC) 为 0.6 μL/mL。光学显微镜下观察发现，经柠檬醛处理的菌丝表现出稀疏、粗糙、扭曲、皱缩、节间分离不规则以及明显的空泡等特征。碘化丙啶和2,7-二氯二氢荧光素二乙酸酯染色结果显示，MIC柠檬醛处理组的菌丝体发出强烈的荧光，平均荧光强度分别是对照组的4.03和8.09倍。此外，柠檬醛处理导致菌丝的脂质含量和干重下降，核酸和蛋白质渗漏增加，孢子外电导率增强，超氧化物歧化酶（SOD）和过氧化氢酶（CAT）活性增强。此外，它还促进过氧化氢（H2O）和丙二醛（MDA）的积累。果实病害接种试验表明，适当浓度的柠檬醛（1/2 MIC，MIC）可显着抑制果实斑点直径的扩大。因此，柠檬醛有望作为一种潜在的替代杀菌剂来控制火龙果采后黑腐病。