Degree

Doctor of Philosophy (PhD)

Department

School of Plant, Environmental, and Soil Sciences

Document Type

Dissertation

Abstract

Plant breeding is crucial for sustaining food production. Rice remains the staple food of over half of the world’s population and a vital economic crop in the U.S., supporting jobs and contributing billions to the economy. However, rice production faces significant challenges from diseases, with rice blast and sheath blight being the most economically damaging in the U.S., causing severe yield losses depending on environmental conditions and disease severity. Breeding disease-resistant varieties offers the most sustainable and cost-effective solution. Advances in molecular breeding, such as Marker-Assisted Selection (MAS) and Genomic Selection (GS), have enhanced breeding efficiency and precision. Additionally, leveraging elite germplasm pools accelerates breeding cycles and optimizes resource use.

This project aimed to enhanced disease resistance breeding in U.S. rice through two main objectives: (1) characterizing blast resistance and identifying/validating resistance loci within U.S. breeding germplasm, and (2) investigating the genetic architecture of sheath blight tolerance and improving breeding approaches to enhance resistance.

Through comprehensive evaluation of U.S. rice breeding germplasm against prevalent Southern U.S. blast races, we observed significant phenotypic variation and high heritability. Genome-wide association studies (GWAS) identified multiple loci, including Pita and a novel resistance locus, qBlast4.1, on chromosome 4. Validated in a bi-parental population, qBlast4.1, conferred broad-spectrum resistance to six of eight evaluated blast races and co-localized with Pi63, reinforcing its role in resistance. Another potential broad-spectrum resistance locus on chromosome 8 warrants further investigation.

For sheath blight, strong heritability and broad phenotypic variation were observed across multiple field evaluations (2022–2024), despite varying disease pressure. A negative correlation between sheath blight resistance, days to heading, and plant height highlights the need to account for these traits in phenotypic evaluations. GWAS identified significant loci, but no single major-effect locus, highlighting the polygenic nature of sheath blight resistance. Given this complexity, GS was explored and demonstrated strong cross-validation prediction accuracies (0.43 for SBTOP and 0.42 for SBBASE), confirming its applicability. In a breeding context, GS effectively enriches populations for sheath blight tolerance and helps eliminate highly susceptible lines.

These findings provide key insights into blast resistance in U.S. rice germplasm and demonstrate the potential of GS to enhance sheath blight resistance in elite U.S. rice breeding germplasm.

Date

3-27-2025

Committee Chair

Famoso, Adam

Download

Available for download on Sunday, March 26, 2028

Share

COinS