Virulence of Pyrenophora tritici-repentis: a minireview

Pyrenophora tritici-repentis is a major wheat pathogen in all wheat (Triticum spp.) growing areas worldwide. Up to date, eight P. tritici-repentis races have been described based on chlorosis, necrosis, or both symptoms caused on race differential wheat genotypes: ‘Glenlea’, 6B662, 6B365, and ‘Salamouni’. Symptom development on differential genotypes depends on the interaction of the pathogen’s necrotrophic effectors named Ptr ToxA, Ptr ToxB, and Ptr ToxC with host susceptibility genes. Ptr ToxA is encoded by the single copy gene ToxA and induces necrosis on sensitive wheat cultivars. Ptr ToxB causes chlorosis and is encoded by the multicopy gene ToxB. The Ptr ToxC is the non-proteinaceous, polar, low molecular mass molecule that also induces chlorosis, but up to date, the gene encoding this toxin is unknown. Races producing Ptr ToxA are predominant in the global Ptr population. There are several reports about new putative races of P. tritici-repentis that do not conform with the current race system, so further research is required. This study aims to collect and systematise available information about the virulence and races of P. tritici-repentis.

Tan spot disease under the lenses of plant pathologists

Necrotrophic plant pathogens pose an important threat to crop production, and many fungi in the Pleosporales have caused the sudden emergence of major epidemics on cereal crops. Tan spot of wheat, caused by Pyrenophora tritici-repentis, is one example, and since its emergence in the 1970s, scientists have explored its virulence and interactions with the host. In this chapter, our aim is to provide a comprehensive review of the most significant landmarks in tan spot research over the past 50 years from a plant pathology perspective.

The first genome assembly of fungal pathogen Pyrenophora tritici-repentis race 1 isolate using Oxford Nanopore MinION sequencing

Objectives The assembly of fungal genomes using short-reads is challenged by long repetitive and low GC regions. However, long-read sequencing technologies, such as PacBio and Oxford Nanopore, are able to overcome many problematic regions, thereby providing an opportunity to improve fragmented genome assemblies derived from short reads only. Here, a necrotrophic fungal pathogen Pyrenophora tritici-repentis (Ptr) isolate 134 (Ptr134), which causes tan spot disease on wheat, was sequenced on a MinION using Oxford Nanopore Technologies (ONT), to improve on a previous Illumina short-read genome assembly and provide a more complete genome resource for pan-genomic analyses of Ptr. Results The genome of Ptr134 sequenced on a MinION using ONT was assembled into 28 contiguous sequences with a total length of 40.79 Mb and GC content of 50.81%. The long-read assembly provided 6.79 Mb of new sequence and 2846 extra annotated protein coding genes as compared to the previous short-read assembly. This improved genome sequence represents near complete chromosomes, an important resource for large scale and pan genomic comparative analyses.

THE EFFECTIVENESS OF BIOLOGICAL FUNGICIDES AGAINST THE SPARE PARTS OF THE LEAVES OF WINTER WHEAT IN THE CONDITIONS OF THE CENTRAL ZONE OF THE KRASNODAR TERRITORY

The biologization of plant growing in modern conditions is becoming an urgent trend in agriculture, which helps to reduce the pesticide load. An important aspect of the transition to organic farming is the use of fungicides based on living microorganisms and their metabolic products to curb the development of diseases. Studies were carried out to assess the effectiveness of modern biofungicides against leaf septoria (Septoria tritici) and yellow spot (Pyrenophora tritici-repentis) of winter wheat - Vitaplan, SP, Gamair, SP, Pseudobacterin-2, Zh, Rizoplan, Zh, Trichocin, SP, Fitosporin -M, SP. Fungicide Amistar Extra, SK was used as a chemical standard. The work was carried out in the conditions of the central zone of the Krasnodar Territory in 2019–2020 on the variety Grom, susceptible to leaf spots. The meteorological conditions of the first year of research were favorable for the development of pathogens of leaf spots. In the second year, conditions were extreme, both for the growth of wheat plants and for the development of phytopathogens. For two years of research, the most effective biofungicides against leaf septoria were Fitosporin-M, SP, Pseudobacterin-2, Zh and Vitaplan, SP, the biological effectiveness was 50.0%, 50.0% and 47.1%, respectively; against yellow spot - Vitaplan, SP and Trichocin, SP, biological efficiency was 48.4% and 45.9%. The use of biological fungicides made it possible to save from 2.5% (Gamair, SP) to 12.6% (Trichocin, SP) of the winter wheat grain yield in comparison with the control (without treatment). The high economic efficiency of the use of biofungicides was established, the maximum net profit was noted in the variant treated with Fitosporin - M, SP (9540 rubles / ha)

Isolate Virulence and Cultivar Response in the Winter Wheat: Pyrenophora tritici-repentis (Tan Spot) Pathosystem in Oklahoma

Prevalence of tan spot of wheat caused by the fungus Pyrenophora tritici-repentis has become more prevalent in Oklahoma as no-till cultivation in wheat has increased. Hence, developing wheat varieties resistant to tan spot has been emphasized, and selecting pathogen isolates to screen for resistance to this disease is critical. Twelve isolates of P. tritici-repentis were used to inoculate 11 wheat cultivars in a greenhouse study in splitplot experiments. Virulence of isolates and cultivar resistance were measured in percent leaf area infection for all possible isolate x cultivar interactions. Isolates differed significantly (P < 0.01) in virulence on wheat cultivars, and cultivars differed significantly in disease reaction to isolates. Increased virulence of isolates detected increased variability in cultivar response (percent leaf area infection) (r = 0.56, P < 0.05) while increased susceptibility in cultivars detected increased variance in virulence of the isolates (r = 0.76, P < 0.01). A significant isolate × cultivar interaction indicated specificity between isolates and cultivars, however, cluster analysis indicated low to moderate physiological specialization. Similarity in wheat cultivars in response to pathogen isolates also was determined by cluster analysis. The use of diverse isolates of the fungus would facilitate evaluation of resistance in wheat cultivars to tan spot.

Genetic polymorphism of ToxB+ Pyrenophora tritici-repentis strains

BACKGROUND: The phytotoxin Ptr ToxB as well as Ptr ToxA is one of the pathogenic factors of Pyrenophora tritici-repentis, that cause leaf chlorosis on susceptible wheat varieties, and is encoded by ToxB gene. P. tritici-repentis strains with ToxB gene are rather rare worldwide. MATERIALS AND METHODS: The object of the study was 37 strains isolated from the leaves of wheat grown in Greece. The virulence of the strains was analyzed and the presence of effector genes as well as the average copy number of ToxB was determined. RESULTS: The race composition of P. tritici-repentis population turned out to be mainly represented by the avirulent race 4 (50% of the strains). Strains of race 1 were not found, while strains of other races were found with a low frequency in the population. All analyzed P. tritici-repentis strains had ToxB gene in the genome, while its homologues and ToxA gene were not detected. The average copy number (R) of ToxB in three P. tritici-repentis strains varied from 0.24 to 1.22. The average copy number of ToxB in the mitotic generation of P. tritici-repentis Gr8 strain, which was characterized by the lowest value of R = 0.24, varied from 0.01 to 0.74 and, on average, turned out to be 2 times higher than in the original strain Gr8. CONCLUSION: Presumably, P. tritici-repentis has a mechanism that gives ToxB+ nuclei an advantage in the division rate over ToxB nuclei. This mechanism indicates the existence of an additional function of this gene that is not associated with pathogenicity.