Phenotypic and marker-assisted characterization of new apple genotypes with high resistance to fire blight

In the period 2016–2018 the susceptibility to fire blight of seven apple genotypes, including four recently bred was assessed. The studies showed that two of the genotypes (J-2003-05 and ‘Early Szampion’) are highly resistant to the disease. The indicator of assessment was evaluated by the size of necrotized part of terminal shoots after their inoculation with strain Ea659 of Erwinia amylovora. The analysis of disease incidence on individual shoots of both genotypes showed no symptoms on 92% and 100% of shoots inoculated in 2016, 83.8 and 77.0% of shoots in 2017, and 87.8 and 77.3% of shoots inoculated in 2018, respectively. Molecular tests based on 16 genetic markers revealed that genotype J-2003-05 possesses 10 resistance alleles (covering the region of interest from LG 3, 5, 7, 10 and 12). This genotype is derived from the cross between ‘Melfree’ and ‘Sawa’ and produces very large dark-red tasty fruits. Genotype ‘Early Szampion’ representing the selected hybrid from the cross of ‘Gold Milenium’ and ‘Sampion’, producing large, bright red, attractive fruits, was found to possess 10 resistance alleles (covering the region of interest from LG 3, 7, 10 and 12), Both genotypes have the prospect of being used in breeding programs and commercial planting.