Micronutrients provide a potentially interesting alternative to fungicides for the protection of crops against fungal pathogens. Here we studied the effect of foliar-applied manganese (Mn) in the form of MnSO4 on severity of anthracnose disease, caused by Colletotrichum lagenarium in cucumber (Cucumis sativus L.) plant. The study was done aimed to characterize the optimum dose and application time of Mn fertilizer on disease suppression as well as to identify the defense mechanisms by which Mn-treated plants resist to fungal disease. In preliminary tests, Mn was applied at different concentrations (1.8, 4.5 and 7.2 mM) and various time points (three days before or two hours before inoculation, or three days after inoculation). Results showed that application of Mn either before or after inoculation suppressed the fungal infection in leaves and cotyledons, with a higher efficiency when applied three days prior to inoculation. However, all applied concentrations of Mn equally reduced the disease severity. Mn treatment in the absence of the pathogen promoted lignification and reactive oxygen species (ROS) accumulation. Also, pre-inoculation Mn treatment enhanced pathogen-induced lignification, callose or ROS production and reduced pathogen-induced cell death. The increase of lignin, callose and ROS induction by Mn application were 34, 30 and 31 % compared to control, respectively. Together, the results suggested the effectiveness of Mn treatments on anthracnose alleviation in cucumber plants. The findings here have a practical importance in plant physiology studies to identify the resistance-relevant mechanisms to pathogens and in sustainable agriculture to control the fungal diseases by a safe method.

中文翻译：

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叶面喷锰诱导黄瓜对炭疽病菌的抗性

微量营养素为保护作物免受真菌病原体侵害提供了一种潜在的令人感兴趣的杀菌剂替代品。在这里，我们研究了叶面施用 MnSO4 形式的锰 (Mn) 对炭疽病严重程度的影响，炭疽病由黄瓜 (Cucumis sativus L.) 植物中的炭疽病引起。该研究旨在表征锰肥对病害抑制的最佳剂量和施用时间，并确定锰处理植物抵抗真菌病害的防御机制。在初步测试中，Mn 以不同浓度（1.8、4.5 和 7.2 mM）和不同时间点（接种前三天或两小时，或接种后三天）施用。结果表明，在接种前或接种后施用锰可抑制叶片和子叶中的真菌感染，接种前三天施用效率更高。然而，所有应用浓度的锰同样降低了疾病的严重程度。在没有病原体的情况下，锰处理促进了木质化和活性氧 (ROS) 的积累。此外，接种前锰处理增强了病原体诱导的木质化、胼胝质或 ROS 的产生，并减少了病原体诱导的细胞死亡。与对照相比，Mn 施用对木质素、胼胝质和 ROS 的诱导分别增加了 34%、30% 和 31%。总之，结果表明锰处理对黄瓜植物炭疽病缓解的有效性。