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Pseudomonas syringae pv. aesculi (Pae) causes bleeding canker, a destructive disease of horse chestnut trees (Aesculus hippocastanum) that limits the breeding of horse chestnut genotypes. The susceptibility of 322 F1 progeny from 20 horse chestnut parent tree sources to the pathogen Pae was evaluated using different inoculation methods. The resulting infection rates, in decreasing order, were caused by inoculation of apical buds, inoculation of annual stems, insertion of bacteria into cut wounds on trunks and foliar spraying of the pathogen. According to the resistance index (RI) results of the field pathogenicity tests, at 2 or 3 years after inoculation 40, 40 and 20 % of horse chestnut parent tree sources were resistant, tolerant and susceptible, respectively, to Pae. Microbiological analyses of plant tissues from buds, phloem in the main trunks and roots of infected F1 progeny regardless of parent tree source showed long-term survival of Pae bacteria in 70 % of tolerant F1 progeny plants that lacked bleeding canker symptoms. Initial RI results and microbial analyses indicated that there was some frequency of resistance in the natural horse chestnut population. Altogether, 41 F1 progeny were the most promising lines based on their viability and the absence of Pae in their tissues.

We analyzed the spreading and persistence of PSTVd variants in several ornamentals in the territory of the Czech Republic. The pool of PSTVd variants detected in Solanum jasminoides, S. muricatum, Datura sp. and Brugmansia sp. was biolistically transferred to Matricaria chamomilla, Argyranthemum frutescens and Diascia sp., species which we found as sensitive hosts for PSTVd from ornamentals. The PSTVd pool showed sequence changes and increased variation after its transfer to potato, suggesting a wide adaptation potential of PSTVd in this crop. Potato exhibited genotype-dependent leaf and spindle tuber symptoms, when inoculated with the sap from S. jasminoides infected with the predominant and sequence-stable PSTVd-S1.