Development of novel detection primers and screening for apple rubbery wood virus 1 and 2 in Germany

Apple rubbery wood disease is globally distributed and affects primarily apples and pears. A characteristic symptom of the disease, which is caused by the two viruses Apple rubbery wood virus (ARWV) 1 and 2 respectively, is enhanced branch and twig flexibility leading to reduced fruit yields. In this study, a highly sensitive RT-PCR detection system was established for reliable and specific detection of all ARWV-1 and ARWV-2 genomic segments, S, M and L, and their variants. Phloem was identified as convenient tissue for reliable ARWV detection. The detection system was applied to 1059 apple samples from German commercial orchards, experimental plots, and variety collections to investigate ARWV distribution across Germany. Overall, ARWV-1, ARWV-2, or mixed infections were identified in 14.2 % of the samples. Commercial orchard samples from thirteen federal states were tested. In eleven federal states ARWV-1 infections ranging from 2.1 % to 16.7 % were detected, in five federal states the ARWV-2 infection status varied from 1.6 % to 12.4 % and in one federal state ARWV-1 and -2 mixed infections were observed. Within the commercial orchard sample set, 47 different apple varieties were tested. Several varieties, highly relevant for apple growers, show ARWV infection rates between 5 % and 10 %. This study provides the first comprehensive overview of ARWV occurrence in German apple orchards and underscores the importance of sensitive diagnostic tools for effective disease monitoring, analysis of planting material and future management strategies.