Dissertation
Phenotypic Characterization and Genetic Dissection of Resistance to Fire Blight in a Pedigree-Connected Apple Breeding Germplasm Set
Doctor of Philosophy (PhD), Washington State University
01/2020
Handle:
https://hdl.handle.net/2376/111257
Abstract
Breeding resistant apple cultivars is a potentially sustainable solution to fire blight, a devastating bacterial disease caused by Erwinia amylovora. However, resistance/susceptibility to fire blight is challenging to phenotype due to E. amylovora strain virulence, differential host × strain interactions, quantitative host resistance, impacts of tree vigor on susceptibility, and environmental influences on disease. Additionally, most resistance alleles at fire blight quantitative trait loci (QTLs) have been characterized in diverse Malus germplasm with poor fruit quality, which reduces the breeding utility of this germplasm for apple scion improvement. The goal of this work was to enable more efficient breeding for resistance to fire blight in apple. This work leveraged two-year fire blight field incidence and severity data in a pedigree-connected apple reference germplasm set and previously curated high-quality genome-wide single nucleotide polymorphism data. The research objectives were: 1) identify or validate elite sources of resistance to fire blight to enable more informed parental selection in apple breeding programs; 2) characterize phenotypic variation for resistance/susceptibility to fire blight in a pedigree-connected germplasm set; and 3) elucidate the genetic basis of resistance/susceptibility to fire blight in breeding relevant germplasm through pedigree-based QTL analysis. Resistance/susceptibility levels of 94 apple cultivars were determined and multiple possible sources of resistance (e.g., ‘Enterprise’, ‘Frostbite’) were identified or validated. Quantitative variation among and within families for fire blight incidence and severity was characterized. Segregation for resistance/susceptibility to fire blight was observed in most full-sib families including families derived from susceptible parents. QTLs associated with resistance/susceptibility were consistently detected on chromosomes (Chr.) 6, 7, and 15. The moderately susceptible breeding parent, ‘Honeycrisp’, was heterozygous for the Chr. 6 QTL and inherited a rare reduced-susceptibility haplotype from its grandparent ‘Frostbite’. Highly resistant ‘Enterprise’ had putative reduced-susceptibility haplotypes at all three QTLs. Implications of this work are 1) increased understanding of resistance/susceptibility to fire blight in germplasm relevant to U.S. apple breeding programs; 2) more informed parental selection; and 3) development and deployment of predictive DNA tests that breeders can use to pyramid favorable alleles and combine superior fruit quality with resistance to fire blight.
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Details
- Title
- Phenotypic Characterization and Genetic Dissection of Resistance to Fire Blight in a Pedigree-Connected Apple Breeding Germplasm Set
- Creators
- Sarah Kostick
- Contributors
- Katherine M Evans (Advisor)Cameron P Peace (Committee Member)John L Norelli (Committee Member)Lee A Kalcsits (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Horticulture, Department of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 197
- Identifiers
- 99900581807801842
- Language
- English
- Resource Type
- Dissertation