# Development of Molecular Markers for Bacterial Leaf Streak Resistance Gene bls2 and Breeding of New Resistance Lines in Rice

## TL;DR

This study develops molecular markers for a bacterial leaf streak resistance gene in rice and breeds new resistant lines with good agronomic traits.

## Contribution

Development of two highly accurate molecular markers for bls2 and breeding of four new BLS-resistant rice lines with no yield penalty.

## Key findings

- bls2 was narrowed down to a 113 kb interval with two markers showing over 98% accuracy.
- Four new rice lines with moderate to high BLS resistance and no agronomic trait trade-offs were developed.
- The resistant lines showed lesion lengths between 0.69 and 1.26 cm, significantly lower than the susceptible variety.

## Abstract

Bacterial leaf streak (BLS) is one of the internationally significant quarantine diseases in rice. Effectively utilizing BLS resistance genes from wild rice (Oryza rufipogon Griff.) to breed new varieties offers a fundamental solution for BLS control. This study focused on the fine mapping of the BLS resistance gene bls2 and the development of closely linked molecular markers for breeding BLS-resistant lines. Using a Guangxi common wild rice accession DY19 (carrying bls2) as the donor parent and the highly BLS-susceptible indica rice variety 9311 as the recipient parent, BLS-resistant rice lines were developed through multiple generations of backcrossing and selfing, incorporating molecular marker-assisted selection (MAS), single nucleotide polymorphism(SNP) chip genotyping, pathogen inoculation assays, and agronomic trait evaluation. The results showed that bls2 was delimited to a 113 kb interval between the molecular markers ID2 and ID5 on chromosome 2, with both markers exhibiting over 98% accuracy in detecting bls2. Four stable new lines carrying the bls2 segment were obtained in the BC5F4 generation. These four lines showed highly significant differences in BLS resistance compared with 9311, demonstrating moderate resistance or higher with average lesion lengths ranging from 0.69 to 1.26 cm. Importantly, no significant differences were observed between these resistant lines and 9311 in key agronomic traits, including plant height, number of effective panicles, panicle length, seed setting rate, grain length, grain width, length-to-width ratio, and 1000-grain weight. Collectively, two molecular markers closely linked to bls2 were developed, which can be effectively applied in MAS, and four new lines with significantly enhanced resistance to BLS and excellent agronomic traits were obtained. These findings provide technical support and core germplasm resources for BLS resistance breeding.