# Molecular Marker-Based Identification of Resistance to Bipolaris sorokiniana in Kazakh and Global Wheat Germplasm

## TL;DR

This study identifies wheat lines resistant to Bipolaris sorokiniana in Kazakhstan and globally, using molecular markers to support breeding efforts in dry regions.

## Contribution

The study identifies new wheat genotypes with stable resistance to Bipolaris sorokiniana and links resistance to Sb1 and Sb2 genes using molecular markers.

## Key findings

- Nine wheat genotypes showed stable resistance to leaf spot blotch across two years under natural infection.
- Six genotypes consistently resistant at the seedling stage carried Sb1, Sb2, or their combination.
- Sb genes were detected in 36 of 50 wheat accessions, including international and Kazakhstani genotypes.

## Abstract

In arid and semi-arid regions, including Kazakhstan, wheat production is severely constrained by diseases caused by Bipolaris sorokiniana. This pathogen infects both root and leaf tissues and may reduce grain yield by more than 30%. The present study aimed to evaluate the resistance of fifty wheat breeding lines to B. sorokiniana under contrasting infection conditions. Field experiments were conducted over two growing seasons under natural infection, artificial inoculation, and fungicide-protected treatments. Disease severity was assessed to identify genotypes with stable resistance across years and environments. In parallel, seedling resistance was evaluated under controlled laboratory conditions to determine early-stage responses to the pathogen. Several wheat lines consistently exhibited low disease severity in the field and expressed resistance at the seedling stage. Genetic analysis revealed that many of these resistant lines carry heritable traits associated with enhanced tolerance to B. sorokiniana. The identified genotypes represent valuable genetic resources for wheat breeding programs aimed at improving disease resistance in dry agricultural regions.

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.