Skip to main content
ARS Home » Northeast Area » Kearneysville, West Virginia » Appalachian Fruit Research Laboratory » Innovative Fruit Production, Improvement, and Protection » Research » Publications at this Location » Publication #347657
Title: Identification of novel strain-specific and environment-dependent minor QTLs linked to fire blight resistance in apples

Author
item DESNOUES, ELSA M-N - Cornell University
item Norelli, John
item ALDWINDKLE, HERB - Cornell University
item Wisniewski, Michael
item EVANS, KATHERINE - Washington State University
item MALNOY, MICKAEL - Fondazione Edmund Mach
item KHAN, AWAIS - Cornell University

Submitted to: Plant Molecular Biology Reporter
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2018
Publication Date: 4/1/2018
Citation: Desnoues, E., Norelli, J.L., Aldwindkle, H.S., Wisniewski, M.E., Evans, K.M., Malnoy, M., Khan, A.M. 2018. Identification of novel strain-specific and environment-dependent minor QTLs linked to fire blight resistance in apples. Plant Molecular Biology Reporter. 36:247-256. https://doi.org/10.1007/s11105-018-1076-0.
DOI: https://doi.org/10.1007/s11105-018-1076-0

Interpretive Summary: Since its first report almost 200 years ago, fire blight, caused by the bacterium Erwinia amylovora, has threatened apple and pear production globally. Epidemics are becoming more common in apple as the varieties and rootstocks being planted are more susceptible, and control is becoming more difficult with the development of antibiotic-resistant strains of the pathogen. The availability of apple varieties with greater genetic resistance to fire blight would be of benefit to growers. However, because pathogens can evolve to overcome genetic resistance and a modern apple orchard is expected to remain in production for 15-25 years, it is important that durable sources of resistance are utilized in breeding. Sources of resistance that have a large effect on disease development and are controlled by a single gene (major gene resistance) are often not durable. Combining multiple sources of low to moderate resistance (minor gene resistance) that act upon different stages of host-pathogen interaction is usually more durable because the possibility for pathogens to mutate quickly at multiple genetic loci is small. When an apple population derived from a cross between a wild apple with moderate resistance to fire blight and domesticated susceptible ‘Gala’ apple was analyzed for its resistance to fire blight, several genetic loci were identified that were associated with small to moderate effects on resistance. The effectiveness of these loci on resistance was strongly affected by both the strain of the pathogen used to evaluate resistance and environmental conditions, and none of loci identified were effective against all strains of the pathogen under all conditions. The potential utility of minor gene resistance in comparison to major gene resistance for the development of new fire blight resistant apple varieties is discussed.

Technical Abstract: Since its first report almost 200 years ago, fire blight, caused by the gram negative bacterium Erwinia amylovora, has threatened apple and pear production globally. Identifying novel genes and their functional alleles is a prerequisite to developing apple cultivars with enhanced fire blight resistance. Here, we report 13 strain-specific and environment-dependent minor QTLs linked to fire blight resistance from a segregating Malus sieversii × Malus × domestica mapping population. Interval mapping at 95% confidence and Kruskal-Wallis analysis at P-value= 0.005 were used to identify QTLs for three strains of E. amylovora differing in virulence and pathogenicity. The QTLs identified, explain a small to moderate part of resistance variability, and a majority were not common between years or E. amylovora strains. These QTLs are distributed in eight linkage groups of apples and comparison of their map position to previously identified fire blight resistance QTLs indicate that most are novel loci. Interaction between experimental conditions in the greenhouse and field, and between years, and differences in virulence levels of strains might be responsible for strain- and year-specific QTLs. The QTLs identified on LG10 for strain Ea273 in 2011 and strain LP101 in 2011, and on LG15 for strain LP101 could be the same QTLs identified previously with strain CFBP1430 in cultivar ‘Florina’ and ‘Co-op16 x Co-op17’ mapping population, respectively. We discuss the potential impact of newly identified minor fire blight QTLs, and major gene-based resistance on the rate of mutation in pathogen populations to overcome resistance and durability of resistance.