The Effect of Viral Infection on the Growth of HoneySweet GM Plum Trees

Plum pox virus (PPV) is one of the most destructive pathogens affecting stone fruit trees. It causes sharka disease and severe yield losses. The genetically modified plum cultivar 'HoneySweet' was developed to provide long-lasting resistance to PPV via RNA interference. Long-term field trials of 'HoneySweet' have been conducted in the Czech Republic since 2001, involving the artificial inoculation of the cultivar with PPV alone, and with apple chlorotic leaf spot virus (ACLSV) and prune dwarf virus (PDV) in combination. This study evaluates the impact of viral infection on tree growth after 24 years in the field. Growth parameters-trunk cross-sectional area (TCSA) and canopy volume-were measured and analysed using ANOVA and Tukey's test. The results show that infected trees exhibit significantly reduced growth compared to non-infected controls, with the strongest inhibition observed in trees inoculated with PPV + PDV + ACLSV. The presence of ACLSV had the most pronounced negative effect on growth, while PDV did not significantly influence tree vigour. These findings emphasise the importance of using virus-free rootstocks and certified planting material to prevent growth suppression in HoneySweet orchards.