Identification and Application of Powdery Mildew and Stripe Rust Resistance Genes to Improve Disease Resistance in Wheat
Genomics and Gene Discovery
Project Number: 5325-21000-019-01
Start Date: Jul 01, 2013
End Date: Jul 01, 2015
Wheat is one of the most important staple food crops worldwide. Powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) and stripe rust caused by Puccinia striiformis Westend. f. sp. tritici (Pst) are two of the most devastating diseases that severely reduce wheat production worldwide. The discovery of resistance genes and their use in breeding are considered an economical and effective way to control both diseases. Due to rapid evolution and appearance of new virulent pathogen races, it is an ongoing process to identify new resistance genes in order to maintain sufficient diversity of resistance in breeding programs. Many of the 60 powdery mildew resistance genes located at 41 loci (Pm1 to Pm44) and 61 stripe rust resistance genes located at 42 loci (Yr1 – Yr42) in common wheat came from cultivated or wild relatives.
Wild emmer, Triticum turgidum var. dicoccoides (2n = 4x = 28; genome AABB), the progenitor of cultivated tetraploid and hexaploid wheats, is rich in genetic diversity for resistances to powdery mildew and stripe rust. Therefore, identification and characterization of the powdery mildew and stripe rust resistance genes in the wild emmer derivatives are necessary for molecular marker assisted selection and utilization of the disease resistance in wheat breeding program.
Molecular marker technologies can accelerate the identification and characterization of disease resistance genes in wheat. Various markers, including restriction fragment length polymorphisms (RFLPs), simple sequence repeats (SSRs), and amplified fragment length polymorphisms (AFLPs), have been used to map a number of powdery mildew resistance genes. Single nucleotide polymorphisms (SNPs) are exchanges of individual bases at the DNA level and represent smallest observable unit of DNA polymorphism. SNP is a ubiquitous type of genetic variation in eukaryotic genomes and ideally suited for construction of high-resolution genetic/linkage maps and association mapping. One of most popular methods is the Illumina SNP genotyping array. Our research unit has been working on wheat SNP project for many years. In collaboration with UC Davis, we developed wheat Illumina GoldGate and Infinium SNP assay platforms to generate first high-density SNP-based genetic map in wheat.
The objective of this proposal is to apply genomics and mapping technologies to develop molecular markers that are tightly linked to powder mildew and strip rust disease resistance genes and used them for marker-assisted selection and pyramiding of the targeted powdery mildew and stripe rust resistance genes in wheat breeding program.
This will be a collaborative research project between USDA-ARS, Genomics and Gene Discovery Research Unit and China Agriculture University (CAU). Prof. Zhiyong Liu from CAU has introduced 380 accessions of wild emmer from Israel and tested their reactions to prevalence isolates of B. graminis f. sp. tritici and P. striiformis f. sp. tritici . Among 380 wild emmer accessions tested, 94% had intermediate to high levels of resistance to local prevalent Bgt isolate E09 and 11% had intermediate to high levels of resistance to local prevalent Pst isolates CYR29, CYR31, CYR32 and CRY33. Crosses have been made between wild emmer accessions and Chinese elite common wheat cultivars and thereafter backcrossed 4-6 times with Chinese commercial varieties to develop powdery mildew and stripe rust resistance breeding lines in wheat breeding program. These mapping population will be used to characterize the powdery mildew and stripe rust resistance genes using molecular marker technologies. Development of molecular markers for genotyping will be carried out in GGD. This project will be funded by Monsanto's Beachell-Borlaug International Scholars Program by providing financial support to a visiting student from Prof. Liu who will spend one and half a year in GGD working on marker development for genotyping of disease resistance genes. In addition, a total of $48,000 will be provided to GGD for lab supplies etc. The student will analyze the existing wheat maps and genomics data and identify sequences for molecular markers for mapping. If necessary, next-generation sequencing technologies will be used to generate sequence data from both resistance and susceptible parental lines for data analysis. Molecular markers that are closely linked to disease resistance traits will be identified and will be further evaluated in different wheat breeding programs for disease resistance when the student goes back to CAU.