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The cyclic plastic deformation of polycrystals leads to the inhomogeneous distribution of the cyclic plastic strain. The cyclic plastic strain is concentrated in thin bands, called persistent slip bands (PSBs). The dislocation structure of these bands generally differs from the matrix structure and is characterized by alternating dislocation-rich and dislocation-poor regions. The mechanisms of the dislocation motion in the PSBs and the formation of the point defects and their migration are quantitatively described. It is shown that, due to localized cyclic plastic straining in the PSBs, persistent slip markings (PSMs) are produced where the PSBs emerge on the surface. They typically consist of a central extrusion accompanied by one or two parallel intrusions. The deep intrusion is equivalent to the crack-like surface defect. The concentration of the cyclic strain in the tip of an intrusion leads to intragranular fatigue crack initiation. The mechanism of the early crack growth in the primary slip plane is proposed and discussed. Numerous PSMs are produced on the surface of the cyclically loaded materials. PSMs contribute to the formation of the surface relief, as well as the relief on the grain boundary. PSMs from one grain impinging the grain boundary are sufficient to create sharp relief on the grain boundary. Void-like defects weaken the grain boundary cohesion and extra material push both grains locally apart. The conditions necessary for the weakening of the grain boundary are enumerated and examples of grain boundary crack initiations are shown. The relevant parameters affecting grain boundary initiation are identified and discussed. The collected experimental evidence and analysis is mostly based on the papers published by the author and his colleagues in the Institute of Physics of Materials in Brno.

Apple cultivars ‘Idared’ and ‘Sampion’ were selected for application of in vitro thermotherapy at 39 ± 0.5°C. The presence of viruses in selected initial trees was detected by enzyme-linked immuno-sorbent assay (ELISA) and reverse transcription polymerase chain reaction (RT-PCR) before the beginning of thermotherapy. Cultivars ‘Idared’ and ‘Sampion’ were both infected with Apple chlorotic leaf spot virus (ACLSV) and with Apple stem pitting virus (ASPV). Cultivar ‘Sampion’ was moreover infected with Apple stem grooving virus (ASGV). Both apple cultivars were successfully multiplied in in vitro cultures on Murashige and Skoog (MS) medium with 1.5 mg l−1 6-benzylaminopurine (BAP). After the end of thermotherapy and transfer to ex vitro conditions, three clones of apple cultivar ‘Idared’ were free of both viruses (ACLSV, ASPV) according to repeated RT-PCR and ELISA. On the contrary, the same viruses (ACLSV, ASGV and ASPV) as in the initial field-grown trees were detected by RT-PCR in all four clones of cultivar ‘Sampion’. Other sanitation and testing of apple cultivars will continue in the following years.

A pentaplex reverse-transcription polymerase chain reaction (Pentaplex RT-PCR) in a single tube was developed for the simultaneous detection of the pome fruit viruses: Apple stem pitting virus (ASPV), Apple stem grooving virus (ASGV), Apple chlorotic leaf spot virus (ACLSV) and Apple mosaic virus (ApMV). This is the first report of the simultaneous detection of all four viruses and host mRNA as an internal specific control. Pentaplex RT-PCR was applied successfully throughout the year, using different plant organs (leaves or dormant buds). The sensitivity of detection by monoplex- and pentaplex RT-PCR assays was comparable. Different combinations of mixed infections of viruses were identified in samples of infected apple and pear trees from different geographical regions. The pentaplex RT-PCR assay developed was sensitive, simple, rapid, and reliable for simultaneous detection of the four viruses in extracts of leaves or dormant buds.