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POSTERS: Plant defense response

Genetic resistance to fire blight in three pear populations maps to chromosome 2
Jason Zurn - USDA-ARS NCGR. Sara Montanari- University of California Davis, John Norelli- USDA-ARS AFRS, Nahla Bassil- USDA-ARS NCGR, Richard Bell- USDA-ARS AFRS

Fire blight, caused by Erwinia amylovora, is a constant problem for pear (Pyrus spp.) growers in the U.S. Resistant cultivars are the best option for managing fire blight. Fire blight resistance has been observed in the cultivars Potomac and Old Home and the selection NJA2R59T69. Mapping populations (‘El Dorado × ‘Potomac’, ‘Old Home’ × ‘Bartlett’, and NJA2R59T69 × ‘Bartlett’) were developed to identify the genomic regions associated with fire blight resistance in these sources. Progeny were genotyped with the recently developed Axiom Pear 70K Genotyping Array. Phenotyping was conducted in 2017 and 2018 by inoculating multiple actively growing shoots of field grown trees with E. amylovora isolate E153n via the cut leaf method. Severity was calculated by determining the percentage of blight on the current season’s shoot. Chromosomal linkage groups were created for each population and an integrated two-way pseudo-testcross approach was used to map QTLs. In each population, a single resistance QTL was identified at a similar region on chromosome 2. Fire blight resistance QTLs have been identified in this region for ‘Harrow Sweet’ and ‘Moonglow’ (parent of ‘Potomac’). The resistance in NJA2R59T69 originated from the P. ussuriensis selection ‘Illinois 76’ and not a P. communis source like ‘Potomac’ and ‘Old Home’. Additional work is needed to further characterize this resistance region.