Nested Association Mapping of Stem Rust Resistance in Wheat Using Genotyping by Sequencing.

Area of Science:

• Plant Genetics
• Agricultural Science
• Molecular Biology

Background:

• Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), poses a significant threat to global wheat production.
• Understanding the genetic basis of adult plant resistance (APR) is crucial for developing durable disease management strategies.

Purpose of the Study:

• To dissect the genetic architecture of stem rust resistance in wheat (Triticum aestivum) using a combination of genotyping by sequencing (GBS) and joint mapping.
• To identify quantitative trait loci (QTL) associated with resistance to North American Pgt races and the Ug99 race group.

Main Methods:

• Generation of F6 recombinant inbred line (RIL) populations from crosses between 10 resistant wheat varieties and one susceptible line (LMPG-6).
• Phenotyping of RILs across multiple environments (Kenya, South Africa, USA).
• Application of joint mapping (nested association mapping) using GBS-derived de novo SNPs to identify QTL.

Main Results:

• Identification of 59 minor and medium-effect QTL distributed across 20 chromosomes, explaining 1%-20% of phenotypic variance.
• Fifteen QTL were consistently detected in multiple environments, indicating robustness.
• Founder parents exhibited differential allelic effects for the identified QTL.

Conclusions:

• Joint mapping combined with GBS is an effective approach for dissecting complex genetic traits like stem rust resistance in wheat.
• The identified QTL provide valuable genomic regions for further investigation into candidate genes conferring resistance.
• This study provides a model for applying GBS-derived SNPs in marker-trait association studies for other plant species.