Document Type : Research Article
Authors
Medicinal Plants Research Center, Institute of Medicinal Plants, ACECR, Karaj, Iran
10.22067/jpp.2026.99511.1287
Abstract
Introduction: Powdery mildew of cucumber, primarily caused by the obligate biotrophic fungus Podosphaera xanthii, represents one of the most destructive foliar diseases affecting cucurbitaceous crops globally. Under optimal greenhouse conditions—typically characterized by moderate temperatures and varying humidity levels—the pathogen rapidly colonizes leaf surfaces, impeding photosynthesis and inducing premature senescence. This ultimately translates to substantial economic losses due to compromised fruit yield and marketability. Historically, the management of this widespread pathogen has relied heavily on the continuous calendar-based application of synthetic chemical fungicides. However, the intensive and singular use of conventional active ingredients has precipitated the emergence of highly resistant pathogenic strains within greenhouse populations. Furthermore, the residual toxicity of synthetic fungicides raises critical concerns regarding occupational hazards for agricultural workers, potential groundwater contamination, and the disruption of non-target organisms. Consequently, there is an urgent demand to develop sustainable, eco-friendly alternatives. Plant-derived secondary metabolites have gained considerable traction as viable biopesticides owing to their complex, multi-site modes of action, which significantly mitigate the risk of resistance development. Building upon this premise, the present study was systematically designed to formulate, characterize, and evaluate the efficacy of a novel emulsifiable concentrate (EC) formulation integrating garlic oil and clove essential oil. The primary objective was to assess its potential as a protective and curative botanical fungicide against cucumber powdery mildew and to ascertain the optimal field-equivalent concentration under controlled greenhouse conditions.
Materials and Methods: To evaluate the fungicidal efficacy of the formulated product, a comprehensive greenhouse experiment was established utilizing a Randomized Complete Block Design (CRD). The experimental setup comprised seven distinct treatments, each replicated three times to ensure robust statistical power and reliability. The treatments evaluated included four concentrations of the botanical EC formulation (0.25%, 0.5%, 0.75%, and 1.0% v/v), a standard commercial synthetic fungicide (Penconazole) serving as a positive chemical control, a commercially available botanical fungicide (Kaliban) as a reference standard, and a water-treated negative control to monitor natural disease progression. The Podosphaera xanthii was collected from naturally infected, untreated cucumber fields. Artificial inoculation of healthy, susceptible cucumber seedlings was executed at the four-leaf phenological stage by gently dusting conidia from heavily infected source leaves onto the target foliage. Following inoculation, the plants were maintained under greenhouse conditions favorable for powdery mildew development. Disease severity was monitored sequentially and quantified utilizing the standardized modified Horsfall-Barratt rating scale to estimate the percentage, for precise visual estimation of infected leaf area. These severity scores were subsequently integrated over the assessment period to calculate the Area Under the Disease Progress Curve (AUDPC), providing a dynamic metric of epidemic development. Additionally, the physicochemical attributes of the EC formulation were thoroughly characterized. Accelerated storage stability tests were conducted to evaluate structural integrity under thermal stress. The chemical profile of the clove essential oil was elucidated using Gas Chromatography-Mass Spectrometry (GC-MS). All experimental data were subjected to analysis of variance (ANOVA) utilizing 9.4 SAS software, treatment means were separated using Duncan's Multiple Range Test (DMRT) at the 5% probability level.
Results and Discussion: The findings demonstrated that all tested concentrations of the botanical EC formulation significantly reduced the severity of cucumber powdery mildew compared to the untreated control (P < 0.05). Notably, a distinct dose-dependent response was documented throughout the trials. Maximum disease suppression was achieved at the 1.0% concentration, which restricted disease progression by 90% relative to the negative control. Statistical analysis revealed that the fungicidal efficacy of the 1.0% formulation was not significantly different from the 0.75% treatment or the conventional synthetic standard, penconazole. However, it exhibited statistically superior performance when compared to both the lower botanical concentrations (0.25% and 0.5%) and the commercial botanical reference, Kaliban. Visual assessment of treated plants revealed no evidence of phytotoxicity, including leaf scorching, or chlorosis across all treated cucumber plants, indicating crop safety at the applied dosage rates. The comprehensive GC-MS analysis of the clove essential oil fraction identified eugenol as the predominantly constituent, accounting for 78.77% of the total compositional profile. Furthermore, the formulation exhibited robust structural integrity during the physicochemical assessments. The EC formulation displayed spontaneity of emulsification in water, generating a homogenous and stable emulsion without creaming or phase separation. Accelerated thermal stress testing confirmed minimal degradation of the active botanical ingredients, while the pH and density remained within the optimal agronomic range, ensuring practical viability for standard agricultural spray equipment and prolonged shelf-life under commercial storage conditions.
Conclusions: The binary EC formulation of garlic oil and clove essential oil represents an eco-friendly management option for cucumber powdery mildew. Specifically, applications at 0.75% to 1.0% concentrations deliver disease control comparable to commercial fungicide standards without compromising plant health. This formulation is well suited for integration into broader Integrated Pest Management (IPM) frameworks and certified organic agriculture. Future field-scale trials evaluating its efficacy on diverse cucurbitaceous cultivars are recommended to validate these findings under natural agroecosystem conditions.
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