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.

A collection of 96 Polish isolates of Phytophthora infestans sampled in the years 2006, 2008 and 2009 were analysed using phenotypic and genotypic markers. Mating type, virulence, resistance to metalaxyl, mitochondrial haplotype and polymorphism at 12 simple sequence repeat (SSR) loci were determined. The majority of isolates were of the A1 mating type, mitochondrial haplotype Ia and sensitive to metalaxyl. Virulence factors against potato R genes R1, R3, R4, R7, R10 and R11 were present in most isolates. Genotyping using SSR markers revealed high genetic diversity within the Polish P. infestans population. Amongst the 96 isolates 66 unique genotypes were identified, 49 of which were observed only in single isolates. Eight isolates of the genotype 13_A2 lineage that has been reported in other parts of Europe were also found in Poland. The implications of these results are discussed.

Fusarium is one of the most important genera of phytopathogenic fungi, causing potato wilt in the field and potato tuber dry rot during storage. The objectives of this study were to identify Fusarium species associated with both potato diseases in different growing regions in Algeria, and to assess their pathogenicity. Among the 152 isolates collected from symptomatic potato plants and tubers in different provinces in Algeria, 13 species of Fusarium and Neocosmospora were identified. Among these three species were isolated only from plants showing symptoms of Fusarium potato wilt (F. oxysporum, F. venenatum, Neocosmospora solani). Two species (F. culmorum, N. tonkinensis) and an isolate of Neocosmospora sp. were found exclusively in tubers with potato dry rot and the remaining ones (F. redolens, F. cf. tricinctum, F. sambucinum, F. cf. incarnatum-equiseti, F. nygamai, F. brachygibbosum and N. falciformis) were associated with both sample types. Fusarium sambucinum was the most frequent species (52.6% of isolates). Fusarium oxysporum and F. nygamai isolates were the most aggressive in the potato wilt pathogenicity test, and F. sambucinum isolates were the most aggressive in the potato tuber pathogenicity test. This is the first study identifying and characterizing potato dry rot and potato wilt pathogens in Algeria.

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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.

Late blight is a devastating and worldwide potato and tomato disease caused by Phytophthora infestans (Mont.) de Bary. The aim of the study was to compare P. infestans isolates collected from potato and tomato plants by determining their virulence, aggressiveness, and sporulation intensity on both hosts in reciprocal testing with the goal of elucidating possible host specialization of the pathogen. Isolates were multiplied on leaflets of their primary hosts. In total, 76 potato-derived P. infestans (P) isolates and 100 tomato-derived P. infestans (T) isolates collected from 2005 to 2007 were studied in detached-leaflet assay experiments. Virulence was assessed on Black's potato differentials R1-R11 and cv. Bzura, as well as on the set of six tomato genotypes, namely cv. New Yorker (Ph-1 gene), Solanum pimpinellifolium L 3708 (Ph-3), West Virginia'63 (Ph-2), West Virginia 700 (Ph-1, Ph-2), Ottawa 30 (Ph-1, Ph-2), and BALU-30 (Ph-1, Ph-2, fruit resistance). Aggressiveness scored as disease severity and sporulation intensity assessed on a 0-3 grade scale were evaluated on leaflets of susceptible cultivars of both hosts. All 176 of the tested isolates were pathogenic to both hosts, indicating that extreme host specialization has not occurred. However, we did observe differences between P and T virulence spectra and their race structures supporting the notion of host adaptation of P. infestans. P and T isolates were more frequently virulent to differentials of their own hosts. P isolates had higher sporulation intensity on their own hosts than on tomato hosts, while for T isolates a similar sporulation intensity was observed on both hosts. Significantly stronger severity of the disease development on T testers was evoked by T isolates. All isolates showed stronger aggressiveness on susceptible potato than on susceptible tomato hosts, and the latter finding indicates a relatively greater suitability of potato host tissue for P. infestans pathogenicity. The host adaptation observed in this study was not conditioned by an ability to evoke disease, but rather by quantitative differences in pathogenic fitness. Genetic characterization of P and T populations is needed to place the present findings in a fuller context.

Phytophthora infestans (Mont.) de Bary is a destructive potato pathogen. Changing weather conditions are among the factors that influence the pathogen population structure. In this study, 237 P. infestans isolates were collected from a single unprotected experimental field in an area with high late-blight pressure located in Boguchwała in the southeastern part of Poland during 15 growing seasons (2000–2014). The isolates were assessed for mating type, mitochondrial haplotype, resistance to metalaxyl, virulence, and polymorphism of 14 single-sequence repeat markers (SSRs). The results revealed 89 unique genotypes among the 237 P. infestans isolates. Eighty-seven isolates belonged to genotype 34_A1, which was detected in all the years of research except 2012. Isolates of P. infestans from individual years were very similar to each other, as shown by Nei’s genetic identity based on 14 SSR markers. The obtained results on isolate characteristics were analyzed in terms of meteorological data (air temperature and precipitation) and indicated that frost, long winters, and hot, dry summers did not directly affect the P. infestans population structure. We described the variability in metalaxyl resistance and virulence among isolates of the P. infestans genotype 34_A1.

Late blight is a disease with the biggest economic impact on potato cultivation worldwide. Pyramiding of the resistance genes originating from potato wild relatives is a breeding strategy that has a potential to produce potato cultivars durably resistant to late blight. Growing such cultivars would allow limiting the intensive chemical control of the disease. The goal of this work was to transfer the late blight resistance gene Rpi-rzc1 from Solanum ruiz-ceballosii to the tetraploid level of cultivated potato and to pyramid it with the Rpi-phu1 gene. We obtained two diploid and, through 4x-2x cross, a tetraploid potato population segregating for the Rpi-rzc1 presence, as well as one diploid and one tetraploid population where both genes were introgressed. In total, 754 progeny clones were tested for resistance to late blight in detached leaflet assays. Pathogen isolates avirulent on plants with both genes and virulent on plants with the Rpi-phu1 were used. The selection was assisted by two PCR markers flanking the Rpi-rzc1 gene and a newly designed, highly specific intragenic marker indicating the Rpi-phu1 gene presence. We obtained 26 diploid and 49 tetraploid potato clones with pyramid of both genes that should enhance the durability and spectrum of their late blight resistance and that can be exploited in potato breeding. The specificity of the marker for the Rpi-phu1 gene and the precision of the Rpi-rzc1 mapping were improved in this work.