Molecular identification and monitoring of major apple tree viruses in Ukraine

Viral diseases of apple trees cause significant economic losses in horticulture in Ukraine, which requires an updated research into their prevalence. The purpose of the study was to assess the prevalence and regional distribution of the main apple tree viruses in industrial plantings of Ukraine using molecular diagnostic methods. The study was conducted by reverse transcription and polymerase chain reaction on 350 samples of apple leaves and bark taken from industrial plantings in five regions of Ukraine. The specificity of detection of three target viruses was confirmed by sequencing the obtained amplicons. The study found that the overall infection rate of apple plantations was 70.6%, which indicates an epiphytic situation. The most prevalent was Apple stem pitting virus (46.0%), whereas Apple chlorotic leaf spot virus and Apple mosaic virus were detected in 36.0% and 13.7% of samples, respectively. Regional analysis revealed the maximum prevalence of viruses in the Zakarpattia (86.0%) and Kyiv (76.3%) regions, while the minimum indicators were recorded in the Kharkiv region (56.8%). A high level of mixed infections was found (25.4%), with a predominance of the combination of Apple stem pitting virus and Apple chlorotic leaf spot virus (18.3%). Also significant is the high percentage of asymptomatic infections (31.2%), which complicates phytosanitary control. The conclusions confirmed that the results obtained justify the need for urgent implementation of a system for molecular monitoring and certification of planting material. The results of the study can be used to develop a national programme for improving apple plantations in Ukraine