Evaluation of old Carpathian apple cultivars as genetic resources of resistance to fire blight (Erwinia amylovora)

In the interests of re-diversifying cultivar use in apple, one of the most important breeding aims, apart from using local cultivars in breeding, is to improve resistance to fire blight (FB). At the Corvinus University of Budapest, the investigation of Hungarian cultivars found in the Carpathian Basin as genetic resources is a major part of the apple breeding program aimed at multiple resistance. The present study, initiated in the early 2000s, evaluates the FB resistance of 31 apple cultivars. Examination of the damage to shoots and flowers, and of the correlation between them, was carried out after artificial inoculation. Two dominant SCAR markers and one SSR marker were used for the genetic analysis of the cultivars giving the best results in phenotypic analysis, in order to detect quantitative trait locus alleles coding for FB resistance. Based on the results of several years of inoculation tests, the assayed cultivars exhibited a wide range of susceptibility levels on the basis of shoot necrosis and in terms of flower damage. A positive correlation (R = 0.058, p = 0.04) was demonstrated between the susceptibility found for the two plant organs. The cultivars Szabadkai szercsika and Sikulai, which gave outstanding results both in the flower and shoot tests and in the genetic analysis, could be suitable genetic resources for resistance breeding programmes. The present work confirmed the complex polygenic nature of FB resistance and the need to identify further markers in addition to those found on linkage group (LG) 3 and LG 7.