KISS, Tomáš

‘Candidatus Phytoplasma spp.’ are pathogenic bacteria that infect many plant species. ‘Candidatus Phytoplasma pyri’, one of the members of the 16SrX group causes pear decline disease that adversely affects pear crops. To describe the prevalence of ‘Ca. P. pyri’ genotypes in the Czech Republic, 143 pear samples were collected from 41 locations including commercial orchards as well as trees along roads. Phytoplasma was detected by PCR in 115 samples, and it was possible to determine imp gene genotype in 84 samples. The most frequent genotypes were A1, B1, and C, which were identified in 71% of phytoplasma positive samples. ‘Ca. P. pyri’ was present either alone or as a mix of two populations in 88% of genotyped samples, and in another 6% of samples it was found in a mixed infection with ‘Ca. Phytoplasma mali’. A sole infection with ‘Ca. Phytoplasma mali’ was observed in 6% of samples. As for symptoms, 19% of symptomatic samples were found to be phytoplasma negative, and 74% of asymptomatic samples proved to be phytoplasma positive; leaf roll was more often observed in phytoplasma positive samples, while leaf narrowing rather indicated the absence of phytoplasma. The mildest symptoms were observed in samples infected with ‘Ca. P. pyri’ of the A1 imp genotype.

‘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.