Abstract
Diseases caused by Bipolaris sorokiniana, expressed as leaf spot blotch (SB) and common root rot (CRR), continue to limit spring wheat production, particularly in dry regions where yield losses may reach 35–40%. This study evaluated resistance to SB and CRR in fifty spring wheat genotypes at both seedling and adult plant stages and identified genetic sources of resistance using molecular markers linked to the Sb1 and Sb2 genes. Field trials were conducted in 2023 and 2024 in the Aktobe region under natural infection, artificial inoculation, and a fungicide-treated background. Based on leaf spot blotch severity quantified as the area under the disease progress curve (leaf AUDPC) under natural infection, nine genotypes displayed stable resistance across both years, while fungicide-treated plots revealed twenty-three resistant genotypes in 2023 and eighteen in 2024. Artificial inoculation identified five resistant lines in 2023 and one in 2024. Resistance to common root rot (CRR) was assessed independently based on subcrown internode (SCI) browning at the adult plant stage. Seedling assays confirmed consistent resistance in six genotypes, all of which carried Sb1, Sb2, or their combination. In total, Sb genes were detected in thirty-six of the fifty accessions, including genotypes from Kazakhstan, Russia, and several other countries. The presence of Sb1 or Sb2 was associated with reduced disease severity, particularly at the seedling stage. These findings identify valuable germplasm for breeding wheat with improved resistance to B. sorokiniana in Kazakhstan.