Breeding apples to withstand infection pressure by fire blight and other diseases

摘要

Commercial cultivars, old varieties and wild species with known resistance against fire blight, caused by the bacterium Erwinla amylovora, were selected as breeding parents. Due to strong fire blight quantitative trait loci (QTLs), the crab apples ‘Robusta 5' and ‘Evereste’ confer virtual immunity against the disease. However, these crab apples lack the characteristics of good fruit quality. In a multilevel phenotypic and molecular selection process, progeny plants were selected based on additional breeding objectives such as agronomic tree features and scab and mildew resistance.‘Ladina’ is a newly named variety and ‘ACV/ 14995', and ‘ACW 11303' are advanced selections with interesting fruit quality. They all carry Rvi6 (Vf) scab resistanceand have a low susceptibility against fire blight based on shoot and flower inoculation tests in the greenhouse. Latent E. amylovora presence was analysed in shoots of plants grown in the greenhouse without visible disease symptoms after artificial inoculation by using quantitative polymerase chain reaction (qPCR). The development of apple cultivars with marketable fruit quality and low susceptibility to E. amylovora and other major apple diseases is especially valuable for organic growing and fruit growing in general.