THE RESULTS OF DETERMINING THE CAUSATIVE AGENT OF POWDERY MILDEW IN CUCUMBER CULTIVATION UNDER GREENHOUSE CONDITIONS IN MONGOLIA

Powdery mildew is one of the most destructive diseases affecting greenhouse cucumber (Cucumis sativus L.) production in Mongolia, causing significant yield losses and increased management costs. The present study aimed to identify the causal agent of cucumber powdery mildew using morphological characteristics and molecular phylogenetic analysis. Cucumber leaf samples exhibiting typical powdery mildew symptoms were collected from greenhouse production systems in five climatically distinct regions of Mongolia. Morphological examination revealed abundant mycelia and conidiophores bearing chains of ovoid to ellipsoid–ovoid conidia. Fibrosin bodies were consistently observed within conidia from all samples, indicating characteristics typical of Podosphaera xanthii. Molecular identification was performed using PCR amplification of the internal transcribed spacer (ITS) region with universal and species-specific primers. PCR results confirmed the presence of powdery mildew fungi, and species-specific amplification identified P. xanthii as the predominant pathogen in three of the five sampled regions. Phylogenetic analysis based on ITS sequences, conducted using the Maximum Likelihood method, demonstrated that the Mongolian isolates clustered within the Podosphaera xanthii clade together with reference sequences retrieved from GenBank. DNA sequences of representative isolates were deposited in the NCBI GenBank database under accession numbers MW939431, MW939432, and MW939433. This study provides the first comprehensive morphological and molecular characterization of cucumber powdery mildew pathogens in Mongolia and confirms Podosphaera xanthii as the primary causal agent under greenhouse conditions. The findings contribute valuable baseline information for the development of effective disease management strategies and future epidemiological studies.