Fireblight (Erwinia amylovora) affects Mal d 1-related allergenicity in apple

Fireblight infection of apple and pear trees is a bacterial disease of serious economic concern. In this study, apple fruits (cultivar "Elstar", "Topaz") from healthy trees and trees naturally infected by the fireblight-causing bacterium Erwinia amylovora, as well as leaves from infected seedlings (cultivar "Golden Delicious"), were analysed for their Mal d 1 allergen concentrations. In addition, trees were treated with the two Aureobasidium pullulans biocontrol strains CF10 and CF40, active ingredients of Blossom Protect FB. Mal d 1, an 18 kDa intracellular protein is the major apple allergen in Northern and Central Europe and is a member of the family 10 of pathogenesis-related proteins, which is upregulated upon stress and pathogen attack. In young symptomless leaves from infected seedlings Mal d 1.01 transcript levels were significantly increased when compared to controls from healthy plantlets. Quantitative Mal d 1 transcript expression in field grown apple fruits did not show significant differences between samples from infected trees and controls. However, Mal d 1 protein content in apple fruits increased in fruits from infected trees. In fruits from trees with fireblight but treated with A. pullulans, Mal d 1 transcript and protein levels were reduced. These data show that an increase of Mal d 1-related allergenicity in fruits may result from fireblight infection. Thus, successful strategies against fireblight are needed to protect the orchards and simultaneously control the allergen content in fruits.