Morphological and Molecular Characterization of Bacterial Pathogens Associated with Leaf Mottle of Sunflower in Northern Kazakhstan

Leaf mottle is a serious disease in the common sunflower (Helianthus annuus L.), which affects plant growth and development and seed quality and yield. Over the past few years, the North Kazakhstan region, a sunflower-producing area in Kazakhstan, has been seriously affected by leaf mottle. Since 2021, symptomatic leaves have been collected from production areas of this base to determine the pathogens causing sunflower foliar diseases. One hundred bacterial strains were isolated, and two genera and five species were identified based on morphological characteristics, molecular genetics, and phylogenetic analysis (16S gene region). The genus Bacillus was represented by four species: Bacillus subtilis, B. megaterium, B. amyloliquefaciens, and B. flexus. The genus Paenibacillus was represented by one species, P. peoriae. Pathogenicity experiments showed that B. subtilis, B. megaterium, B. flexus, and P. peoriae could cause leaf mottle disease symptoms. However, disease symptoms caused by B. flexus were highly similar to those observed on infected leaves under natural conditions in the field. Therefore, these bacterial isolates were found to be the primary pathogens causing sunflower leaf mottle, and B. flexus was the most common and virulent pathogen in this study. In addition, this is the first report of B. megaterium, B. flexus, and P. peoriae as pathogens associated with sunflower leaf mottle in Kazakhstan.