Background. The spot blotch disease caused by the hemibiotrophic fungus Bipolaris sorokiniana has become a serious problem for barley. Utilization of resistant or tolerant barley cultivars ensures sustainable diversity conservation and environmentfriendly crop production. Thus, supplying barley breeders with sources of resistance to harmful diseases is an urgent task. Materials and methods. A set of 100 barley accessions, earlier selected for different levels of resistance to B. sorokiniana, served as the material for this study. Eleven isolates of B. sorokiniana of various geographic origin, belonging to 4 pathotypes, were used for testing. The resistance of barley seedlings was assessed under controlled laboratory conditions, and that of adult plants under artificial infection pressure in the field. Responses to B. sorokiniana were scored using the 0–9 rating scale.Results and conclusions. Barley genotypes with race-specific resistance to the spot blotch causative agent were identified. The percentage of barley genotypes resistant to five isolates of B. sorokiniana pathotype 1 averaged 24.2%; two isolates of pathotype 3, 29.5%; three isolates of pathotype 7, 18.3%; and one isolate of pathotype 0, 37%. Barley accessions manifesting resistance in their seedlings, but susceptible in the phase of milk-wax ripeness, and vice versa, with seedling susceptibility and adult resistance, were identified. Six (6) barley genotypes showed seedling and adult resistance to pathotype 1, nine (9) to pathotype 3, and two (2) to pathotype 7. No barley accessions resistant to all isolates of the pathogen were found.

Aims: To evaluate responses to four strains of potato spindle tuber viroid (PSTVd) and to mixed viroid/viral infection of modern potato cultivars. Study Design: Four PSTVd strains were used to evaluate the tolerance of potato varieties: VP35 (LC523658), VP87 (LC523667), FP10-13 (LC523676), and NicTr-3 (LC654171). These strains were chosen based on their different geographic origin and their different aggressiveness against a highly susceptible tomato cv. Rutgers. Place and Duration of Study: Laboratory of Plant Resistance to Diseases of All-Russian Institute of Plant Protection, St. Petersburg, between January 2022 and May 2024. Methodology: The study included 39 modern potato cultivars of different origin. Transcripts of four PSTVd strains were used to inoculate tomato plants of the cv. Rutgers. Before PSTVd inoculation with tomato sap, all potato plants were tested for viral infection by ELISA. The presence of PSTVd in infected plants was verified by RT-PCR as well as by RT-qPCR. Results: The strain-specificity in the response of 39 cultivars to viroid infection was revealed. Five types of symptoms on tubers were identified at 90 dpi. Five cultivars were identified in which, after the first inoculation of plants with all PSTVd strains, normal in shape tubers were formed. Average tuber weight for PSTVd- infected plants was more than twice and a half time less compared to mock-inoculated plants (P < 0.05). All plants of the next generation derived from infected but normally shaped tubers showed strong symptoms of disease. After three cycles of continuous propagation in tomato cv. Rutgers PSTVd strains became less aggressive to potato cultivars. Mixed viroid/viral infection lead to an increase manifestation of tuber deformation only for certain cultivars. Conclusion: The strain specificity of the majority of cultivars in terms of the degree of symptom development after the first inoculation was established. Five cultivars were symptomless after the first inoculation with four strains but were found to have severe viroid symptoms in plants obtained from PSTVd-infected tubers. No synergism in the manifestation of mixed viroid/viral infection symptoms on tubers was found.

Background. It is known that the pathological phenotype of potato plants can be mediated by complementary interactions between the genomic RNA of PSTVd and mRNA of some regulatory genes, which consequently lead to RNA interference, the synthesis of small interfering RNAs (vd-sRNA PSTVd), and impaired morphogenesis. At the same time, symptoms caused by the viroid may vary in different potato cultivars. Here we predict the interactions between the 3’ UTRs of various alleles of the StTCP23 transcription factor gene and the complementary regions in PSTVd genomic RNA. Materials and methods. We selected eight commercial potato cultivars with different symptoms of viroid infection and disease. For each cultivar, six clones of each cDNA amplicon of StTCP23 with a 3’ UTR were identified, and the allelic compositions of the target regions within their 3’ UTRs were characterized. Results. In total, 11 types of alleles of the 3’ UTR StTCP23 segment complementary to the vd-sRNA PSTVd were identified. Cultivars with the A allele (‘Gala’, ‘Colomba’, ‘Favorit’, and ‘Fioletovy’) identical to the reference genome or a high dose of the C allele with a deletion of four nucleotides (cv. ‘Impala’) were characterized by high susceptibility already at the primary (firstyear) infection with the PSTVd. Cvs. ‘Krepysh’, ‘Labadia’ and ‘Riviera’, classified as tolerant during primary inoculation, on the contrary, were characterized by the absence of the A allele and the presence of cultivar-specific mutant alleles. Conclusion. A high degree of polymorphism in the target site (3’ UTR region) of StTCP23 indicates a possible selection pressure on this locus. It can be assumed that cultivars with shorter alleles, which have fewer bases complementary to vd-sRNA in hypothetical duplexes and therefore less likely to induce target gene silencing, are more tolerant to the PSTVd upon primary viroid infection.

Phytophthora infestans is the oomycete that causes potato blight, an important disease. The potato spindle tuber viroid (PSTVd) is a dangerous pathogen of many plants, including potato. We have previously shown that PSTVd can be transmitted from infected potato plants into the Ph. infestans mycelium, replicated within the mycelium, and then transmitted to other potato plants upon their infection with Ph. infestans in laboratory conditions. The objective of this work was to check the hypothesis that PSTVd transmission, preservation, and replication in Ph. infestans are possible to occur in natural conditions during long-term coevolution of the host and pathogen in the Solanum spp.– Ph. infestans system. A screening test for PSTVd was performed in 111 natural Ph. infestans isolates obtained from potato plants, which represented various cultivars, had signs of potato blight, and were collected from industrial potato fields of the Moscow, Vologda, and Bryansk regions and breeding and variety test plots of the St. Petersburg and Moscow regions in 2020 and 2022. Using RT–PCR with PSTVd-specific primers, 42 Ph. infestans isolates collected in 2020 were tested after five passages and 69 Ph. infestans isolates collected in 2022, after a single passage on rye agar. Diagnostic amplicons were detected in 8 and 50 isolates, respectively. Some of the amplicons were visually assessed as minor amplification products, apparently resulting from nonspecific priming on a host Ph. infestans gene, which codes for a hypothetical protein-coding mRNA in Ph. infestans and other oomycetes. Eight amplicons were sequenced to verify the PSTVd presence in Ph. infestans isolates. Three amplicons corresponded to the complete PSTVd genome and five, to its part (~260 bp). The nucleotide sequences of cloned amplification products were identified to species in the BLAST system and deposited in GenBank. The amplicons obtained with the PSTVd-specific primers were identified as PSTVd sequences in all Ph. infestans isolates examined. The majority of the nucleotide sequences were phylogenetically related to BLAST sequences of PSTVd strains originating from Russia; several strains showed similarity to strains from other countries (France, China, and West African countries). The results demonstrate that PSTVd was for the first time detected in natural (field) Ph. infestans isolates and offer new opportunities for studying the intricate multilevel host–parasite interactions.

Barley net blotch is an economically important disease. The causative agent is an ascomycete, Pyrenophora teres, which exists in two forms: P. teres f. teres (Ptt) and P. teres f. maculata (Ptm), which differ in their symptoms on barley plants. These two forms are easily crossed in laboratory conditions with the formation of fertile offspring, however, it is extremely difficult to prove the hybrid nature of fungal isolates, sometimes found in natural populations of the pathogen and bearing signs of both forms. In 2020, we first identified Ptt × Ptm hybrids in natural populations of P. teres in Krasnodar Region in isolates collected in 2016. The aim of the studies was to compare the virulence of two Ptt isolates, two Ptm isolates of different origin and a hybrid isolate Ptt × Ptm to a wide set of barley genotypes from the VIR collection pre-selected for Ptt resistance, to determine variability of the virulence trait in the hybrid isolate and characterize resistance to both forms of the fungus and hybrid. Depending on the barley genotype, 3 types of disease symptoms were manifested upon inoculation with the Ptt × Ptm hybrid isolate: (1) similar to Ptt, (2) similar to Ptm, and (3) a mixed type. Apparently, the manifestation of symptoms after inoculation with the hybrid isolate depends on the barley genotype influencing the expression of certain pathogen effector genes. It was shown that in most cases Ptm isolates differ in virulence from Ptt isolates to the same barley genotypes, and the Ptt × Ptm hybrid isolate from both Ptt and Ptm. On average, the Ptt × Ptm hybrid isolate was less aggressive than the Ptt and Ptm isolates. A comparison of the types of responses of barley genotypes to all studied isolates of Ptt and Ptm revealed 8.8% of genotypes resistant to both forms of P. teres and 5.6% to Ptt, Ptm and the hybrid isolate Ptt × Ptm. The virulence of natural hybrid between two forms of P. teres Ptt × Ptm was studied for the first time. The barley genotypes resistant to the two forms of the net blotch are valuable source of resistance for barley breeding.

Two forms of the pathogenic fungus Pyrenophora teres, P. teres f. teres (a net form) and P. teres f. maculata (a spot form), cause different disease signs, net or spot blotch, on barley leaves. The net form of P. teres is widespread wherever barley is cultivated, while the spot form was first identified in Krasnodar krai of Russia in 2011 and Brest oblast of Belarus in 2016. The two forms of the pathogen easily mate each other in laboratory conditions, but their hybrids either do not form or are difficult to detect in nature. The question as to whether hybrids between the net and spot forms are produced and maintained in natural populations is pressing and bears applied significance because different genes determine resistance to the different P. teres forms in barley. Hybrid forms may be virulent to resistance donors used in breeding. The objective of this work was to search Russian and Belarussian natural populations for hybrids between P. teres f. teres and P. teres f. maculata with the use of new form-specific markers, Ptt and Ptm. The study included 138 single-conidium isolates from four P. teres f. maculatа and four P. teres f. teres populations. The isolates were collected from commercial barley plantations of Leningrad oblast, Krasnodar krai (Russia), and Brest oblast (Belarus) from 2013 to 2016. A genotyping with 10 form-specific markers was performed in all isolates. Several isolates were found to combine markers of both of the P. teres forms and were conventionally identified as hybrids between the forms. Hypotheses were advanced to explain the occurrence of hybrids in natural populations. The most plausible hypothesis suggests that sexual or somatic hybridization between the two forms coexisting in barley plantations accounts for the origin of the P. teres isolates that combine markers specific to P. teres f. teres and markers specific to P. teres f. maculata in their genomes. It is also possible that a third, possibly ancestral, intermediate form was preserved during divergence in the species P. teres.

Background The potato spindle tuber viroid (PSTVd) is the smallest of all known potato pathogens. PSTVd is a circular, single-stranded RNA molecule that does not code for proteins. Symptoms caused by PSTVd lead to a significant reduction in tuber yield or death of the plant. PSTVd infection triggers the silencing of host-plant genes and induces disease symptoms in the plant via vd-sRNA. The StTCP23 potato gene which encodes a transcription factor is one of the targets of PSTVd. The aim of the study was to assess the effect of inoculation of potato plants of cv. ‘Colomba’ with the PSTVd viroid NicTr-3 strain on the StTCP23 expression in infected plants.Materials and methods. Potato plants of cv. ‘Colomba’ were inoculated with leaf sap of the tomato cv. ‘Rutgers’ in which the PSTVd viroid NicTr-3 strain was propagated. RT-PCR with specific primers was used to confirm the infection of potato plants with the viroid. Diversity of RNA molecules in the PSTVd population was revealed using RT, cloning, and sequencing of the viroid. The expression of the StTCP23 gene in infected potato plants was assessed by quantitative PCR with the ef1α gene as a reference.Results. Symptoms of infecting ‘Colomba’ plants with the PSTVd viroid strain NicTr-3 were not detected, while the presence of the viroid in potato leaves was confirmed by molecular methods. Ten mutations were found in individual variants of the PSTVd strain NicTr-3, responsible for reducing the viroid’s aggressiveness. An increase in the expression of StTCP23 was shown at 3 time points in ‘Colomba’ plants inoculated with the NicTr-3 strain compared to the control.Conclusion. The mechanism of interaction between PSTVd and the StTCP23 gene in an infected potato plant is not universal and depends both on the potato genotype and viroid strain. Additional studies are required to prove the existence of specific interaction mechanisms between the host-plant and viroid strain genotypes.

Potato spindle tuber viroid (PSTVd) is a small infectious non-coding circular RNA causing diseases of important crops, including tomato and potato. The symptoms vary from mild to severe depending on the viroid strain, the host plant variety, and the environmental conditions. The molecular mechanisms underlying the development of particular disease phenotypes remain elusive. The PSTVd strain NicTr-3 causes severe disease symptoms on Solanum lycopersicum cv. Rutgers and Solanum tuberosum cv. Colomba. It was found that after three cycles of propagation in tomato cv. Rutgers, infection of potato cv. Colomba with NicTr-3 resulted in very mild symptoms including smaller size of tubers and delayed leaf senescence. Sequence analysis of PSTVd clones isolated from tomato inoculum revealed the presence of mutated variants of genomic RNA. Transcriptome analysis carried out on leaves showed a considerable difference between infected and healthy plants at 14 dpi and 30 dpi. Interestingly, the response of potato plants to the attenuated PSTVd strain revealed a large number of DEGs associated with initiation of dormancy with a considerable increase in the vegetation period. The second vegetative generation (tuber-derived plantlets from control healthy and PSTVd-infected plants) was characterized by similar phenotypes and transcriptomes. Thus, here we describe a case of attenuation of a severe PSTVd strain after continuous propagation in tomato. It would be of interest to consider the attenuated viroid strains as a potential biocontrol agent or vaccine against this type of pathogenic RNA.

Wheat stripe rust (YR) caused by Puccinia striiformis f. sp. tritici ( Pst ), poses a significant threat to global food security. Resistance genes commonly found in many wheat varieties have been rendered ineffective due to the rapid evolution of the pathogen. To identify novel sources of adult plant resistance (APR), 292 accessions from the N.I. Vavilov Institute of Plant Genetic Resources, Saint Petersburg, Russia, were screened for known APR genes (i.e. Yr18 , Yr29 , Yr46 , Yr33 , Yr39 and Yr59 ) using linked polymerase chain reaction (PCR) molecular markers. Accessions were evaluated against Pst (pathotype 134 E16 A+ Yr17+Yr27) at seedling and adult plant stages across multiple years (2014, 2015 and 2016) in Australia. Phenotypic analyses identified 132 lines that potentially carry novel sources of APR to YR. Genome-wide association studies (GWAS) identified 68 significant marker-trait associations (P<0.001) for YR resistance, representing 47 independent quantitative trait loci (QTL) regions. Fourteen genomic regions overlapped with previously reported Yr genes, including Yr29 , Yr56 , Yr5 , Yr43 , Yr57 , Yr30 , Yr46, Yr47 , Yr35 , Yr36 , Yrxy1 , Yr59 , Yr52 and YrYL . In total, seven QTL (positioned on chromosomes 1D, 2A, 3A, 3D, 5D, 7B and 7D) did not collocate with previously reported genes or QTLs, indicating the presence of promising novel resistance factors. Overall, the Vavilov diversity panel provides a rich source of new alleles which could be used to broaden the genetic bases of YR resistance in modern wheat varieties.

докторскую диссертацию «Селекция полукарликовых сортов озимой мягкой пшеницы».Сегодня Л.А.Беспалова -признанный лидер среди селекционеров не только нашей

The most widespread and harmful disease of barley is net form of net blotch caused by the ascomycete Pyrenophora teres f. teres Drechsler (Ptt). A cost effective and environmentally sustainable strategy for barley protection against Ptt is to develop barley cultivars possessing genetic resistance. In previous GWA analysis, we identified SNP-markers associated with a resistance locus on chromosome 3H in the interval of 45.82–54.53 cM. These SNPs have been described previously in the literature to be located within the same region of chromosome 3H. The aim of the study was to validate QTL markers controlling resistance to Ptt on chromosome 3H in this region by KASP genotyping in four F2 populations of crosses between the resistant cultivars, Morex, Fox, and Zolo, and the accession, Local k-21578, with the susceptible barley cv. Gesine and in a doubled haploid (DH) population of Canadian Lake Shore (CLS)/Harrington. Eleven of fifteen studied markers showed high efficacy (97.5–100%) for co-segregation with resistance to Ptt in the DH population, CLS/Harrington. Three of these markers located at 54.53 cM and one at 51.27 cM were effective in two F2 populations of crosses of Morex and Fox with susceptible cv. Gesine. These markers are also located close to each other on the physical map (442,203,921–443,119,491 bp). Apparently, in cultivars, CLS, Morex, and Fox, resistance to Ptt is determined by the same locus. Markers JHI-Hv50k-2016-166392 (47.1 cM, 112,536,071 bp), Clone ID 3255462_1 (51.63 cM, 363,531,898 bp), and Clone ID 3255462_2 (51.63 cM, 363,531,871 bp) showed high efficacy in the DH population and in the F2 population, Local k-21578/Gesine. Apparently, at least two loci controlling Ptt resistance exist in the chromosome region of 47.0–54.3 cM: one at 46.0–48.44 cM and another at 51.27–54.8 cM. These regions were found to harbor several genes involved in important plant functions, including disease response and signaling pathways. Allele-specific PCR markers were developed based on the KASP assay data and tested on six resistant, two moderately resistant, and two susceptible barley genotypes. Four markers were found to be effective to differentiate susceptible and resistant barley genotypes. The KASP and allele-specific PCR markers associated with Ptt resistance on chromosome 3H will be useful for pyramiding resistance QTLs in barley marker-assisted selection.

Potato spindle tuber viroid (PSTVd) is a harmful quarantine disease with wide geographic distribution. To date, experimentally proved resistance or tolerance of potato cultivars to PSTVd has not been reported. The aim of this study was to evaluate responses to four PSTVd strains of 39 modern potato cultivars of different origin. Four PSTVd strains of different origin, the intermediate VP35, VP87, and two sever strains FP10-13 and NicTr-3, deposited in GenBank, were used. Transcripts of these strains were used to inoculate tomato plants of the cv. Rutgers. Before PSTVd inoculation with tomato sap, all plants were tested for viral infection by ELISA. The presence of PSTVd in infected plants was verified by RT-PCR as well as by RT-qPCR at sixty days post-inoculation (dpi). The strain-specificity in the response of cultivars to viroid infection was revealed. Five cultivars were identified in which, after the first inoculation of plants with all PSTVd strains, normal in shape tubers were formed. All plants of the next generation derived from infected but normally shaped tubers showed strong symptoms of disease. PSTVd and mixed viroid/viral infection (PVY + PSTVd, PVM + PSTVd, and PVY + PVS + PSTVd) led to a significant decrease in the number and weight of tubers in most of the cultivars studied.

Background. Among the weeds of the Solanaceae family, a potential viroid infection reservoir, black nightshade (Solanum nigrum L.), is ubiquitous in Russia.Materials and methods. Molecular diagnostics of the viroid was performed using RT-PCR with the P3/P4 primers specific for PSTVd and 6Pospi F/R specific for the Pospiviroidae family of viroids. The amplification products were cloned and sequenced, and the nucleotide sequences were deposited in the GenBank database.Results. RT-PCR showed that 80–100% of plants were infected with PSTVd. The cDNA amplicons of two plants from Nizhny Novgorod (Sn1 and Sn2) and one plant from Tula Province (Sn3) were cloned (3 clones each) and sequenced. An analysis of the nucleotide variability in the clones revealed significant genetic differences between the PSTVd strains, independent of the geographical origin. Mutations U120C and U192C, compared with the reference strain VP35 (LC523658), were found in all 9 clones. The Sn1 isolate was close to the “potato” VP35 isolate and differed from it only by three mutations. The Sn2 isolate was represented by three identical clones and differed from VP35 by nine mutations, while Sn3 had 22 mutations in the region of 49–310 nucleotide positions in total for three clones. After artificial infection of healthy S. nigrum plants in a greenhouse, the presence of PSTVd in infected plants was confirmed and it was proved that the viroid was transmitted by seeds to plants of the next generation.Conclusion. For the first time in externally healthy plants of S. nigrum, widely distributed in the potato fields of Russia (Nizhny Novgorod and Tula Province), the potato spindle tuber viroid, PSTVd, was detected. It was proved that the viroid was preserved in the seeds of S. nigrum and transmitted to their progeny. Genetic heterogeneity of PSTVd strains from S. nigrum plants was found. Two mutations, U120C and U192C, were common for all tested clones of PSTVd strains.

Direct sequencing is the gold standard for genome haplotyping, while PCR is used for detection of limited number of genetic variations. However, these methods are not suitable for fast low-cost in-field testing of plant specimens. Here, we developed a two-color florescent nanosensor system (named here biplex deoxyribozyme nanomachine or bixDNM) that can haplotype dsDNA amplicons. The sensor is based on fluorescent binary deoxyribozyme embedded in a nanostructure containing together four DNA binding arms. Two allele specific sensors were tailored for producing signals at two different wavelengths (525 and 662 nM) only in the presence of fully matched analytes. Accurate haplotyping of seven barley samples was achieved. This is the first technique showing detected of both short (146 bp) and long (1348 bp) dsDNA amplicons with single nucleotide specificity. The study demonstrated bixDNM can become a foundation for future development of a plant haplotyping technology that can be used in field or at the low resource agricultural settings.

Potato spindle tuber viroid (PSTVd) is a naked, circular, single-stranded RNA (356–363 nucleotides in length) which lacks any protein-coding sequences. It is an economically important pathogen and is classified as a high-risk plant quarantine disease. Moreover, it is known that PSTVd is mechanically transmitted by vegetative plant propagation through infected pollen, and by aphids. The aim of this study is to determine the possibility of viroid transmission by potato pathogen Phytophthora infestans (Mont.) de Bary. PSTVd-infected (strain VP87) potato cultivars Gala, Colomba, and Riviera were inoculated with P. infestans isolate PiVZR18, and in 7 days, after the appearance of symptoms, re-isolation of P. infestans on rye agar was conducted. RT-PCR diagnostics of PSTVd in a mixture of mycelia and sporangia were positive after 14 days of cultivation on rye agar. The PSTVd-infected P. infestans isolate PiVZR18v+ was used to inoculate the healthy, viroid-free plants of potato cv. Gala and tomato cv. Zagadka. After 60 days, an amplification fragment of PSTVd was detected in the tissues of one plant of tomato cv. Zagadka by RT-PCR with the primer set P3/P4, indicating successful transmission of PSTVd by P. infestans isolate PiVZR18v+. This result was confirmed by sequencing of the RT-PCR amplicon with primers P3/P4. The partial sequence of this amplicon was identical (99.5 %) to PSTVd strain VP87. RT-PCR showed the possibility of viroid stability in a pure culture of P. infestans isolate PiVZR18v+ after three consecutive passages on rye agar. PSTVd was not detected after the eighth passage on rye agar in P. infestans subculture. These results are initial evidence of potato viroid PSTVd being bidirectionally transferred between P. infestans and host plants.

Viroids belong to a very interesting class of molecules attracting researchers in phytopathology and molecular evolution. Here we review recent literature data concerning the genetics of Potato spindle tuber viroid (PSTVd) and the mechanisms related to its pathological effect on the host plants. PSTVd can be transmitted vertically through microspores and macrospores, but not with pollen from another infected plant.The 359 nucleotide-long genomic RNA of PSTVd is highly structured and its 3D-conformation is responsible for interaction with host cellular factors to mediate replication, transport between tissues during systemic infection and the severity of pathological symptoms. RNA replication is prone to errors and infected plants contain a population of mutated forms of the PSTVd genome. Interestingly, at 7 DAI, only 25 % of the newly synthesized RNAs were identical to the master copy, but this proportion increased to up to 70 %at 14 DAI and remained the same afterwards. PSTVd infection induces the immune response in host plants. There are PSTVd strains with a severe, a moderate or a mild pathological effect. Interestingly, viroid replication itself does not necessarily induce strong morphological or physiological symptoms. In the case of PSTVd, disease symptoms may occur due to RNA-interference, which decreases the expression levels of some important cellular regulatory factors, such as, for example, potato StTCP23 from the gibberellic acid pathway with a role in tuber morphogenesis or tomato FRIGIDA-like protein 3 with an early flowering phenotype. This association between the small segments of viroid genomic RNAs complementary to the untranslated regions of cellular mRNAs and disease symptoms provides a way for new resistant cultivars to be developed by genetic editing. To conclude, viroids provide a unique model to reveal the fundamental features of living systems, which appeared early in evolution and still remain undiscovered.

To investigate the current status of viroid infection in potato fields in Russia, potato spindle tuber viroid (PSTVd) and chrysanthemum stunt viroid (CSVd) were detected in potato (Solanum tuberosum) and S. nigrum plants growing in the Volga (V), North-Western (NW), and Far Eastern (FE) federal districts in Russia. While both PSTVd and CSVd were detected in potato samples from the V and FE regions, only CSVd was detected in potato samples from NW. CSVd was detected in S. nigrum from FE, and this was the first detection of CSVd in S. nigrum. Analysis of the complete genomes of 30 PSTVd and 10 CSVd variants revealed that 5 and 7 PSTVd variants from V and FE, respectively, and 2, 4, and 3 CSVd variants from V, NW, and FE, respectively, were new. Analysis of the infectivity of and symptoms caused by 15 Russian PSTVd isolates in tomato revealed that 14 PSTVd isolates caused intermediate or severe symptoms, and only FP14 caused mild symptoms. Our survey revealed that most of the Russian PSTVd isolates from V and FE caused intermediate symptoms in tomato, and the genome sequences were identical to that of PSTVd isolated from S. demissum. Phylogenetic analysis of nucleotide sequences of the Russian PSTVd variants showed their close relationship to previously studied PSTVd isolates, suggesting that most strains in Russia have not substantially changed genetically, but have widely spread in potato fields.

Potato viral disease has been a major problem in potato production worldwide including Russia. Here, we detected Potato Virus M (PVM), P (PVP), S (PVS), Y (PVY), and X (PVX) and Potato Leaf Roll Virus (PLRV) by RT-PCR on potato leaves and tubers from the Northwestern (NW), Volga (VF), and Far Eastern (FE) federal districts of Russia. Each sample was co-infected with up to five viruses. RT-PCR disclosed all six viruses in NW, three in VF, and five in FE. Phylogenetic analyses of PVM and PVS strains resolved all PVM isolates in Group O (ordinary) and all PVS isolates in Group O. Seven PVY strains were detected, and they included only recombinants. PVY recombinants were thus the dominant potato virus strains in Russia, although they widely varied among the regions. Our research provides insights into the geographical distribution and genetic variability of potato viruses in Russia.

The genetic control of virulence was studied in four isolates of the fungus Pyrenophora teres f. teres, originating from various geographic regions in experiments with nine barley accessions, possessing known resistance genes. Experiments were performed with the ascospore progeny of two crosses. The results of segregation for virulence in the progeny of direct crosses were confirmed by analysis of backcrosses and sib crosses. One to four genes for avirulence toward various barley genotypes were found in the isolates under study. It is suggested that dominant suppressor genes are involved in the genetic control of avirulence toward four barley genotypes.

Viroids belong to a very interesting class of molecules attracting researchers in phytopathology and molecular evolution. Here we review recent literature data concerning the genetics of Potato spindle tuber viroid (PSTVd) and the mechanisms related to its pathological effect on the host plants. PSTVd can be transmitted vertically through microspores and macrospores, but not with pollen from another infected plant. The 359 nucleotidelong genomic RNA of PSTVd is highly structured and its 3D-conformation is responsible for interaction with host cellular factors to mediate replication, transport between tissues during systemic infection and the severity of pathological symptoms. RNA replication is prone to errors and infected plants contain a population of mutated forms of the PSTVd genome. Interestingly, at 7 DAI, only 25 % of the newly synthesized RNAs were identical to the master copy, but this proportion increased to up to 70 % at 14 DAI and remained the same afterwards. PSTVd infection induces the immune response in host plants. There are PSTVd strains with a severe, a moderate or a mild pathological effect. Interestingly, viroid replication itself does not necessarily induce strong morphological or physiological symptoms. In the case of PSTVd, disease symptoms may occur due to RNA-interference, which decreases the expression levels of some important cellular regulatory factors, such as, for example, potato StTCP23 from the gibberellic acid pathway with a role in tuber morphogenesis or tomato FRIGIDA-like protein 3 with an early flowering phenotype. This association between the small segments of viroid genomic RNAs complementary to the untranslated regions of cellular mRNAs and disease symptoms provides a way for new resistant cultivars to be developed by genetic editing. To conclude, viroids provide a unique model to reveal the fundamental features of living systems, which appeared early in evolution and still remain undiscovered.