Morphological and Molecular Identification of Uromyces betae Causing Rust Disease on Sugar Beet and Swiss Chard

Abstract

Rust disease symptoms characterized by chlorotic spots, reddish-brown pustules, premature leaf senescence, and reduction in foliar quality were observed on sugar beet and Swiss chard cultivated under humid and moderate temperature conditions. Symptomatic leaf samples collected from infected fields were subjected to pathogen isolation and identification using morphological and molecular approaches. Microscopic examination of infected tissues revealed abundant uredinia and telia containing globose to ellipsoidal urediniospores with echinulate walls, characteristic of Uromyces betae. Considerable variation in pustule density, spore production, and lesion distribution was observed among samples collected from different host plants and cultivation areas. Pathogenicity tests conducted on healthy sugar beet and Swiss chard plants reproduced typical rust symptoms, including pustule formation and progressive foliar damage, whereas non-inoculated control plants remained symptom-free. Re-isolation and microscopic confirmation of the pathogen from inoculated tissues fulfilled Koch’s postulates and verified the pathogenic nature of the fungus. Molecular characterization was performed through amplification and sequencing of the internal transcribed spacer (ITS) region and additional conserved loci associated with rust fungi identification. Sequence analysis demonstrated high similarity between the obtained isolates and authenticated U. betae sequences available in public databases. Phylogenetic analysis grouped the isolates within the U. betae lineage with strong bootstrap support, confirming species identity and genetic relatedness among regional isolates. Environmental conditions characterized by prolonged leaf wetness and moderate temperatures strongly favored spore germination, infection, and disease development. Severe infections reduced photosynthetic leaf area and negatively affected crop quality and productivity. Integrated morphological and molecular approaches provided reliable identification and differentiation of U. betae from other rust pathogens associated with leafy vegetable crops.