Fusarium spp. belong to the division Ascomycota and cause important plant diseases; these fungi may contaminate food products with mycotoxins, endangering human and animal health. Several Fusarium spp. have been associated with potato dry rot. The most frequent and devastating of these species are F. sambucinum, F. solani and F. oxysporum, depending on the geographic location and the season. Samples of potato tubers with dry rot symptoms were collected, and their putative fungal isolates were identified as Fusarium species using partial nucleotide sequences of the internal transcribed spacer, translation elongation factor 1-α and β-tubulin genes. Among 149 isolates, 12 species were identified. F. oxysporum was the most frequent (45 % of the isolates), followed by F. avenaceum (12.1 %), F. solani (10.7 %) and F. sambucinum (7.4 %). Phylogenetic analyses confirmed the species identifications and revealed a high diversity of F. solani and a low diversity of F. oxysporum. Potential producers of zearalenone and trichothecenes were identified within the obtained isolates using PCR markers. Isolates that were pathogenic to potatoes in laboratory tests were found in four species: F. sambucinum, F. avenaceum, F. culmorum, and F. graminearum. The effects of increased temperature and mixed inoculum on the pathogenicities of chosen species were evaluated. This study adds 434 potato-derived Fusarium sequences to the NCBI GenBank database and demonstrates that the list of Fusarium species and mycotoxins present in potato tubers may be richer than previously believed, regardless of whether these species cause dry rot or live as saprophytes.

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This study describes late blight resistance of potato breeding lines resulting from crosses between cultivar 'Sárpo Mira' and Rpi-phu1 gene donors. The progeny is investigated for the presence of Rpi-Smira1 and Rpi-phu1 resistance (R) genes. Interestingly, in detached-leaflet tests, plants with both R genes withstood the infection of the Phytophthora infestans isolate virulent to each gene separately, due to either interaction of these genes or the presence of additional resistance loci. The interaction was studied further in three chosen breeding lines on the transcriptional level. The Rpi-phu1 expression, measured over 5 days, revealed different patterns depending on the outcome of the interaction with P. infestans: it increased in infected plants whereas it remained low and stable when infection was unsuccessful. The expression patterns of P. infestans effectors Avr-vnt1, AvrSmira1, and Avr8, recognized by the Rpi-phu1, Rpi-Smira1, and Rpi-Smira2 genes, respectively, were evaluated in the same experimental setup. This is the first report that the Avr-vnt1 effector expression is not switched off permanently in virulent isolates to avoid recognition by an R protein but can reappear in a postbiotrophic phase and is present constantly when infecting plants without the corresponding R gene. Both a plant and a pathogen can react to the other interacting side by changing the transcript accumulation of R genes or effectors.

The Rpi-rzc1 gene originates from Solanum ruiz-ceballosii, a wild diploid relative of the cultivated potato. It provides high levels of resistance to late blight both in detached leaflet and in tuber slice tests. Here, we present evidence on the broad-spectrum of this resistance using detached leaflet assays and 509 diverse Polish Phytophthora infestans isolates of which only seven (1.4 %) were virulent on plants with the Rpirzc1 gene. In a previous mapping study genetic distance between the Rpi-rzc1 gene and locus F conferring violet flower colour was 3.4 cM, while on the other side the gene was flanked by marker T1521 located in the distance of 6.1 cM. Adding new RenSeq markers changed the map order and slightly decreased these distances. To further increase the precision of the genetic map we expanded the mapping population with another 240 individuals originating from the same cross. These individuals were assessed for resistance to P. infestans in detached leaflet tests and their flower colours were evaluated. Ten sequence-specific PCR markers were scored in the enlarged mapping population: two were derived directly from the NBS-LRR homologs from the potato genome sequence, two were identified by the Resistance Gene Enrichment Sequencing (RenSeq) approach, and the remaining six from other mapping studies. On the resulting map the Rpi-rzc1 gene is flanked by markers located 0.4 cM from it. Narrowing down the chromosome sector containing the Rpi-rzc1 gene to 1 cM improves the efficiency of marker-assisted selection and will be useful for studies aiming at cloning the gene.

Resistance breeding is a very important alternative to chemical control of late blight. Many resistance (R) genes from the wild Solanum species have been discovered and introduced into the cultivated potato. The laboratory methods to assess the resistance to late blight such as tests on detached leaflets, leaves, tuber slices, or whole tubers, are easy, cheap, fast and provide a good estimation of resistance that can be further confirmed in field trials for the selected material. Laboratory assessment is particularly useful for materials, in which major resistance genes segregate and the resistance is qualitative rather than quantitative.