Ondrášek, Ivo

The distribution of ‘Candidatus Phytoplasma prunorum’, a phloem-limited pathogen, varies among plant tissues during the year, but knowledge about quantitative comparisons of its presence in roots and above-ground tissues across Prunus species remains limited. The variation in ‘Ca. P. prunorum’ in four Prunus species was monitored monthly during 2025 using quantitative PCR-based absolute quantification. Roots, one-year-old shoots and annual shoots were sampled monthly from 21 infected trees of Prunus armeniaca, Prunus domestica, Prunus persica and Prunus salicina. Phytoplasma titer varied with plant part and sampling month, and differences were also observed among the examined host groups. Because cultivar and rootstock were linked to species, these differences cannot be attributed to species alone. Roots provided the most consistent year-round detection, whereas above-ground tissues showed stronger monthly variation during the studied period. P. domestica displayed the most distinct pattern: roots remained frequently positive, while one-year-old shoots and particularly annual shoots had lower detection rates and lower phytoplasma titers. Multilocus genotyping detected ten multilocus profiles, but their uneven distribution among only 21 trees precluded a reliable evaluation of their relationship with phytoplasma titer or symptom expression.

‘Candidatus Phytoplasma prunorum’, the causal agent of European stone fruit yellows (ESFY), is one of the most important pathogens causing considerable economic losses in stone fruit orchards. This study evaluated trees infected and noninfected by phytoplasma ESFY of 16 apricot varieties grown in an orchard in Lednice (Czech Republic) between the years 2008-2014. Pomological traits, phenophases, pollen germination and seed viability were analysed as well as the presence of ‘Ca. P. prunorum’ in pollen, flower organs, fruit flesh, immature seeds and seedlings by nested PCR. One of the most detrimental impacts was the decreased fruit set of infected trees which occurred in 12 out of 16 studied varieties reaching an average fruit set decrease of 16.1%. Pollen germination rates also suffered, showing an average decrease by 11.78% in infected trees. In the analysis of some traits, overall significant differences were observed between the infected and noninfected trees. However, for all analysed traits in different varieties, both positive and negative influences of phytoplasma ESFY were observed. The presence of ‘Ca. P. prunorum’ in infected trees was confirmed in flower parts (only in peduncle in 70.2% of cases) and fruit parts (immature fruit flesh in 42.0% and milky kernels in 26.2% of cases), however, neither in seedlings nor in pollen.