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Triggering the plant resistance induction phenomenon by chemical compounds, for example acibenzolar-S-methyl ester, has been known and described in scientific literature. Other benzothadiazole derivatives have been also described, however, their properties have not been sufficiently studied. The tested substance, N-methyl-N-methoxyamide-7-carboxybenzo(1.2.3)thiadiazole (BTHWA), is an amide derivative of benzothiadiazole, showing a stimulating effect on plant growth, apart from its plant resistance inducing activity. This article presents the impact of BTHWA, used solo and in the program with fungicides, on the strawberry plants development, fruits health, yield, and quality parameters of the crop. The results show that the combined use of BTHWA and fungicides had a positive impact on the plants health and fruit health and nutraceutical and nutritional composition of compounds when compared to the results obtained when strawberries were treated only with the BTHWA or the fungicide. As a result of BTHWA use, the partitioning of assimilates has changed, which directly translated into the results of the conducted experiments. A reduction in the respiration of the fruit during storage was also observed, possibly due to a reduced disease infestation and a lower dry matter content in the fruit. A correlation between the parameters determined during the experiment was found. The BTHWA mode of action was evidenced to be beneficial to strawberry plants and fruit.

The relationship between housekeeping and pathogenicity-related genes and virulence or avirulence towards the primary Malus resistance genes (R) has not been previously studied for Venturia inaequalis fungus, the causal agent of apple scab. In this study, the sequences of two housekeeping genes encoding elongation factor alpha (EF-1α) and β-tubulin and two previously unstudied effector genes of V. inaequalis from mannosidase and glucosidase families of 100 strains collected from apple cultivars with Rvi6, Rvi1, and Rvi17 and without known scab resistance genes were submitted to the analyses. Based on the phylogenetic and diversity data, as well as recombination analyses of the sequenced regions, we assessed the phylogenetic relationships and genetic structure of the pathogen within the species and the evolutionary forces that are currently acting upon this microorganism. The topology of the obtained phylograms demonstrates the lack of a relationship between the phylogenetic position of the strain and the host cultivar and the geographical origin or race of the strain. The isolates from different hosts were differentiated but did not form diagnosable, distinct phylogenetic groups. These results suggest that the analyzed genes may be too conserved to reflect the adaptation of pathogens to apple genotypes with different R genes, thus, they do not adequately reflect race discrimination. In contrast, based on variation and gene flow estimation, genetic divergence was observed among strains virulent to apple trees containing Rvi6. The results of this study confirmed a lack of free recombination between strains and demonstrated that the analyzed regions are in linkage disequilibrium and contain non-random polymorphisms associated with the strain.

During the summers of 2013–2014, symptoms similar to viscid rot and upright disease were observed on cranberries (Vaccinium macrocarpon) on one plantation in central Poland. The associated fungi were isolated from symptomatic plant tissue. On the basis of morphological and cultural characteristics and the ability of isolated fungi to elicit viscid rot symptoms on cranberry fruits, they were classified as the genus Diaporthe. Further analysis of ITS sequence data allowed for the classification of the newly obtained isolates as D. vaccinii. Additional analysis of genetic diversity using five RAPD and eight ISSR primers constituted additional confirmation of genetic distance existing between closely related D. vaccinii and D. eres species, enabling their differentiation.

Bull's eye rot is the most important storage disease of apples, causing up to 30-40% crop yield losses on susceptible cultivars in Poland. Due to the intensive plant material exchange, the knowledge about the species composition of causal agent of the disease needs to be updated. In this study, a previously modified multiplex PCR assay (Gariepy et al., 2003) was applied for the identification of the fungi in pure cultures. In years 2014-2015, 497 isolates of Neofabraea spp. from 493 samples of symptomatic fruit collected from 8 cold storages located in different regions of Poland were identified. Neofabraea alba was the predominant species (87% of the isolates) followed by N. perennans and N. kienholzii represented by 10 and 3% of the isolates, respectively. The species N. malicorticis was not detected. For the determination of genetic diversity, representative isolates of N. alba (25), N. perennans (22) and N. kienholzii (10) were analyzed by ISSR PCR with 5 microsatellite markers. The resulting dendrogram comprising results of all five ISSR reactions, segregated all strains according to their species affiliation. No relations were found between the observed amplification pattern and the geographical origin of the strain.

Background Tracking newly emergent virulent populations in agroecosystems provides an opportunity to increase our understanding of the co-evolution dynamics of pathogens and their hosts. On the one hand host plants exert selective pressure on pathogen populations, thus dividing them into subpopulations of different virulence, while on the other hand they create an opportunity for secondary contact between the two divergent populations on one tree. The main objectives of the study were to explore whether the previously reported structure between two Venturia inaequalis population types, virulent or avirulent towards Malus x domestica cultivars carrying Rvi6 gene, is maintained or broken several years after the first emergence of new virulent strains in Poland, and to investigate the relationship between ‘new’ and ‘native’ populations derived from the same commercial orchards. For this purpose, we investigated the genetic structure of populations of the apple scab fungus, occurring on apple tree cultivars containing Rvi6, Rvi1 or Rvi17 resistance gene or no resistance at all, based on microsatellite data obtained from 606 strains sampled in 10 orchards composed of various host cultivars. Results Application of genetic distance inferring and clustering methods allowed us to observe clear genetic distinctness of the populations virulent towards cultivars carrying Rvi6 gene from the Rvi6-avirulent populations and substructures within the Rvi6-group as a consequence of independent immigration events followed by rare, long-distance dispersals. We did not observe such a structuring effect of other genes determining apple scab resistance on any other populations, which in turn were genetically homogenous. However, in two orchards the co-occurrence of strains of different virulence pattern on the same trees was detected, blurring the genetic boundaries between populations. Conclusions Among several resistance genes studied, only Rvi6 exerted selective pressure on pathogens populations: those virulent toward Rvi6 hosts show unique and clear genetic and virulence pattern. For the first time in commercial Malus x domestica orchards, we reported secondary contacts between populations virulent and avirulent toward Rvi6 hosts. These two populations, first diverged in allopatry, second came into contact and subsequently began interbreeding, in such way that they show unambiguous footprints of gene flow today. Electronic supplementary material The online version of this article (10.1186/s12862-018-1122-4) contains supplementary material, which is available to authorized users.

Brown rot caused by fungi belonging to the genus Monilinia is one of the major limiting factors of sour and sweet cherry production. Up to now, three species, M. fructigena, M. laxa and M. fructicola, have been identified as causal agents of brown rot on cherries worldwide. From 2010 to 2013, during the monitoring of cherry orchards in different areas of Poland, a fourth species, M. polystroma, was isolated from brown rot symptoms on sour and sweet cherry fruits. To the best of the authors’ knowledge, this is the first time M. polystroma has been reported as the causal agent of brown rot on cherries. The genetic diversity of M. polystroma isolates from cherries and other hosts was analysed using PCR MP, ISSR and RAPD techniques and showed its clear distinctness from other Monilinia spp. tested. The cluster analysis of fingerprinting data revealed a high similarity of M. polystroma isolates from Poland and their close relationship with the reference strain from Japan, indicating that this species is a recently introduced pathogen. The highest genetic distance between the examined isolates and the highest number of different genotypes was observed in an ISSR assay. Detailed genetic diversity characteristics revealed that M. polystroma isolates from cherries did not create a distinct group but were intermingled with M. polystroma isolates from other hosts. The results of the pathogenicity test conducted on different fruit species indicated a lack of host specificity for M. polystroma isolates.

Based on partial sequence analysis of the β-tubulin gene, 19 isolates of fungi causing bull's eye rot on apple in Poland were classified into species: Neofabraea alba, N. perennans and N. kienholzii. To the authors’ knowledge, the detection of N. kienholzii is the second in Europe and the first in Poland. Species affiliation of these fungi was confirmed by a new species-specific multiplex PCR assay developed on the basis of previously published methods. The new protocol allowed for the specific identification of bull's eye rot-causing species, both from pure cultures and directly from the skin of diseased or apparently healthy apples. In 550 samples of diseased fruits collected from nine cold storage rooms located in three regions of Poland, in 2011 and 2012, N. alba was detected as the predominant species causing bull's eye rot, occurring on average in 94% of the tested samples. Neofabraea perennans was found in a minority of apple samples, N. kienholzii was found only in two apple samples, while N. malicorticis was not detected in any sample tested. In tests on 120 apparently healthy fruits, only N. perennans was detected in a single sample. The results of genetic diversity analyses of bull's eye rot-causing fungi based on the β-tubulin gene sequence and an ISSR (inter-simple sequence repeat) PCR assay with two primers were consistent, showing the expected segregation of tested isolates with respect to their species boundaries. However, the genetic distance between N. perennans and N. malicorticis was very low, as reported previously.

Cherry leaf spot (Blumeriella jaapii) is the most dangerous disease of orchards and nurseries of stone fruit trees, especially sour cherries. Chemical method is the primary tool for controlling cherry leaf spot. Dodine, benzimidazole and triazole fungicides are the most commonly used. The frequent application of these fungicide groups resulted in the development of resistant forms of the causal agent to their active substances. In years 2012–2015 in 33 selected sour cherry orchards located in central Poland, the occurrence of resistant forms of B. jaapii to dodine and benzimidazoles was determined by using a spore germination test on the poisoned agar medium. The study showed high resistance to thiophanate-methyl in 15 orchards, and to dodine in 5 orchards. The medium resistance to thiophanate-methyl and dodine occurred in 7 orchards. Low level of resistant forms to thiophanate-methyl was found in 11 orchards, and to dodine – in 21. The obtained results will be the basis for implementation of cherry leaf spot control programs in regard to appropriate antiresistance guidelines.

Brown rot, caused by fungi belonging to the genus Monilinia, is one of the most important diseases of stone and pome trees in the world. During the summers of 2010 and 2011, a total of 670 Monilinia spp. isolates were obtained from infected fruits. They were collected from different commercial stone and pome fruit orchards, located in northern, southern and central Poland. All isolates were identified using multiplex PCR. Twenty isolates obtained from plum, peach and apple fruits were identified as M. polystroma and 5 isolates from plums as M. fructicola. The remaining isolates were identified as M. fructigena or M. laxa. The identification of the isolates was also confirmed on the basis of growth characteristics in culture according to the EPPO standard PM 7/18. A comparison of morphological features of four Monilinia spp. growing on two selective growth media, APDA-F500 and CHA, indicated significant differences between these species. In artificial inoculation of fruits, all the examined Monilinia spp. isolates were pathogenic. The species affiliation of M. polystroma and M. fructicola isolates collected from orchards in Poland was confirmed on the base of phylogenetic and sequence analysis of the internal transcribed spacer (ITS1/5.8S rDNA/ITS2) region of ribosomal DNA.

Fourteen primers were designed specific to SNP (G → C mutation) in the cytochrome b gene of Venturia inaequalis, corresponding to G143A substitution related to strobilurin resistance. Specificity of the primers and amplification efficiency were preliminarily tested in conventional PCR at different annealing temperatures. The performance of several preselected primer sets was verified in real-time PCR with SYBR Green I dye. Finally, two primer sets ('2Wt' and '5Mt') were successfully applied for discrimination between wild-type and mutated allele. Different sensitivity of the detection of homologous and non-homologous DNA corresponded to the difference in Ct values equalled 10.5 for '2Wt' and 12.0 for '5Mt' primer set. Primers specific to Mycosphaerella fijensis cytochrome b sequence (Wille et al. 2002) were applied for additional control of PCR inhibitors. The reliability of the new method was evaluated and verified using two series of reference DNA dilutions and artificial mixtures of both types of DNA. Developed real-time PCR assay was applied to measure the ratio of mutated to non-mutated allele in field samples, collected in Poland in 2009, using two series of reference DNA in every run. The measured mutation level for the samples derived from orchards with conventional chemical control was very high (50-100%). For two populations originating from one organic orchard, the measured level of mutation was 1% and 46%. The combination of molecular and traditional tests for the evaluation of mutation level and monitoring of resistance levels in orchards is recommended.

BGPI : équipe 5; International audience; Plant pathogens adapt readily to new crop varieties in agrosystems, and it is crucial to understand the factors underlying the epidemic spread of new virulent strains if we are to develop more efficient strategies to control them. In this study we used multilocus microsatellite typing, molecular epidemiology tools and a large collection of isolates from cultivated, wild and ornamental apples to investigate the origin of new virulent populations of Venturia inaequalis, an ascomycete fungus causing apple scab on varieties carrying the Rvi6 resistance gene. We demonstrated a common origin at the European scale of populations infecting apples (Malus × domestica) carrying the Rvi6 resistance and Malus floribunda, the progenitor of the Rvi6 resistance. Demographic modeling indicated that the Rvi6-virulent lineage separated several thousands of years ago from populations infecting non-Rvi6 hosts, without detectable gene flow between the two lineages. These findings show that 'breakdowns' of plant resistance genes can be caused by the selection and migration of virulent genotypes from standing genetic variation maintained in environmental disease reservoirs, here ornamental crabapples. This work stresses the need to take better account of pathogen diversity in resistance screenings of breeding lines and in resistance deployment strategies, in order to enhance sustainable disease management.

Crown and leather rot of strawberry caused by Phytophthora spp. are major soil diseases of cultivated strawberry (Fragaria × ananassa) in Poland. In this study, in total 45 isolates of Phytophthora spp. from plants of cultivars Elsanta, Honeoye, Florence, Camarosa, Roxana, Onebor, Alba, Elegance, Albion, Senga Sengana and Malwina originating from crowns (20 isolates) and fruits (25 isolates) as well as 25 soil samples from the same fruiting strawberry plantations located in central, north-eastern, and south-eastern regions of Poland were identified. Among them, 44 isolates from plant organs and eight from soil samples were identified as Phytophthora cactorum and from one plant and one soil sample as P. citricola; of those remaining from the soil, one was identified as P. citrophthora and one as P. cryptogea. Identifications were based on morphological characteristics and DNA analyses. Species-specific polymerase chain reaction confirmed the presence of Phytophthora spp. in all positive examined plant and soil samples and confirmed that P. cactorum is predominantly responsible for crown and leather rot diseases of strawberry in monitored regions of Poland. Pathogenicity tests showed that all isolates of Phytophthora spp. originating from soil derived from strawberry plantations were pathogenic both to strawberry and to raspberry.