Screening of apricot hybrids for resistance to Plum pox virus

The successful control of sharka disease is based on a complex of measures and approaches. The most beneficial and economically and ecologically sound approach for minimizing losses caused by the disease is the growing of resistant cultivars. Because of this, the apricot breeding program of the Fruit Growing Institute, Plovdiv, Bulgaria, aimed to obtain cultivars that are resistant to Plum pox virus (PPV), the causal agent of sharka, and, at the same time, possess good fruit quality and economic parameters. In that respect, during 2009-2014, F1 apricot hybrids were created by cross-pollination between resistant or partially resistant cultivars well adapted to Bulgarian agro-ecological conditions. The F1 individuals were grown under natural background near stone-fruit trees infected predominantly by the M strain of PPV. During 2014-2015, a total of 341 individuals from 13 hybrid families were screened for PPV resistance. The screening included a) field observations for sharka symptoms, b) serological analysis and c) genotyping by using sets of molecular markers located in a locus linked to PPV resistance in the apricot genome (marker-assisted selection; MAS). According to the MAS results from screening with two sets of molecular markers, 93 individuals (27.27%) of all analysed individuals, originating from eight hybrid families, were genotyped as resistant. On the basis of the screening data for resistance and some agronomic evaluations of the fruits, a few hybrids from the crosses `Harlayne' x 'Harcot' and `Harcot' x 'SE0' have been artificially inoculated for further scoring.