Septoria tritici blotch (STB) is caused by the ascomycete Zymoseptoria tritici and one of the predominating diseases in wheat (Triticum aestivum) in Europe. The control of STB is highly reliant on frequent fungicide applications. The primary objective of this study was to assess sensitivity levels of Z. tritici to different fungicide groups. The fungicides included in this study were epoxiconazole, prothioconazole-desthio, tebuconazole, and fluxapyroxad. A panel of 63 isolates from Estonia, Latvia, and Lithuania, and 10 isolates from Finland were tested. Fungicide sensitivity testing was carried out as a bioassay analyzing single pycnidium isolates on different fungicide concentrations. The average EC 50 value in Baltic countries and Finland to epoxiconazole was high ranging from 1.04 to 2.19 ppm. For prothioconazole-desthio and tebuconazole, EC 50 varied from 0.01 to 0.24 ppm, and 1.25 to 18.23 ppm, respectively. The average EC 50 value for fluxapyroxad varied from 0.07 to 0.33 ppm. To explain the range of sensitivity, the samples were analyzed for CYP51 and Sdh mutations, as well as cytb G143A, CYP51 overexpression, and multidrug resistance (MDR). Frequencies of ZtCYP51 mutations D134G, V136A/C, A379G, I381V, and S524T in the Finnish-Baltic region were lower than in other European countries, but have increased compared to previous years. The frequency of cytb G143A conferring strobilurin resistance also augmented to 50-70% in the Z. tritici populations from Estonia, Finland, Latvia, and Lithuania. No Sdh mutations were found in this study, and neither strains of MDR phenotypes. However, we found a strain harboring a previously unknown transposon insertion in the promoter of the MFS1 gene, involved in drug efflux and multi-drug resistance. This new insert, however, does not confer an MDR phenotype to the strain.

High-throughput sequencing technologies were used to identify plant viruses in cereal samples surveyed from 2012 to 2017. Fifteen genome sequences of a tenuivirus infecting wheat, oats, and spelt in Estonia, Norway, and Sweden were identified and characterized by their distances to other tenuivirus sequences. Like most tenuiviruses, the genome of this tenuivirus contains four genomic segments. The isolates found from different countries shared at least 92% nucleotide sequence identity at the genome level. The planthopper Javesella pellucida was identified as a vector of the virus. Laboratory transmission tests using this vector indicated that wheat, oats, barley, rye, and triticale, but none of the tested pasture grass species (Alopecurus pratensis, Dactylis glomerata, Festuca rubra, Lolium multiflorum, Phleum pratense, and Poa pratensis), are susceptible. Taking into account the vector and host range data, the tenuivirus we have found most probably represents European wheat striate mosaic virus first identified about 60 years ago. Interestingly, whereas we were not able to infect any of the tested cereal species mechanically, Nicotiana benthamiana was infected via mechanical inoculation in laboratory conditions, displaying symptoms of yellow spots and vein clearing evolving into necrosis, eventually leading to plant death. Surprisingly, one of the virus genome segments (RNA2) encoding both a putative host systemic movement enhancer protein and a putative vector transmission factor was not detected in N. benthamiana after several passages even though systemic infection was observed, raising fundamental questions about the role of this segment in the systemic spread in several hosts.

Pyrenophora teres (net blotch) and Cochliobolus sativus (spot blotch), the most widely spread diseases in the Northern Baltic region, have high impact on cereal production. The effect of three levels of fertilisation and two fungicide treatments on the severity of barley diseases, grain yield and quality traits (protein content, test weight, thousand kernel weight (TKW), grading) was tested during a period of three years. Weather conditions during the growing season highly determined disease severity, yield and quality. In addition, the infection level of P. teres was more dependent on fungicide treatment (p ≤ 0.001) and barley variety (p ≤ 0.001) while C. sativus infection was influenced more by fertilisation (p ≤ 0.001) and year x fertilisation interaction (p ≤ 0.001). Fungicide treatment had no influence on grain yield and protein content, but slightly improved TKW (p ≤ 0.05), test weight (p ≤ 0.001) and grading (p ≤ 0.001). However, these quality traits were mostly influenced by barley variety (p ≤ 0.001). TKW and test weight were highest at fertilisation level N80P12K43. The effect of year and fertilisation contributed significantly to the grain protein content. Grain yield and protein content were highest at the maximum fertiliser application (N100P15K54).

Efficacy of the fungicide tebuconazole was tested in 2 treatment regimes in 3 spring barley varieties over three years (2003)(2004)(2005). The impact of the fungicide on the control of major barley pathogens Pyrenophora teres and Cochliobolus sativus, as well as kernel yield was studied in the course of field trials. The fungicide treatments had a strong impact on the control of infection of P. teres and increased kernel yield in variable disease infection conditions. For the more resistant genotype, fungicide application had relatively low returns because of the much higher level of biological resistance and small disease-related yield reductions. For the susceptible genotype, severe disease infection caused bigger yield reduction, not compensated by the use of fungicides. Use of fungicide demonstrated the highest economic return in the case of the moderately susceptible barley variety.

Ramularia leaf spot (RLS) is a disease of barley (Hordeum vulgare) caused by the fungus Ramularia collo-cygni Sutton & Waller (Rcc). Rcc causes necrotic lesions, premature senescence of leaves, and yield reduction. Under Estonian conditions, there are usually no leaf spots on the upper leaves of barley prior to flowering. In 2009, 2010, and 2012, symptoms similar to those of RLS were observed on leaves of spring and winter barley in several Estonian agricultural regions. Approximately 30% of the plants in affected fields were symptomatic. Symptoms were not observed in 2011, which was a dry and hot year. Initial symptoms were small brown spots, beginning on the upper leaves (flag leaf, F-1 leaf) at the flowering growth stage (4). Later, the spots spread to the sheaths, stems, and awns and became necrotic. The lateral margins of the spots were delimited by the leaf veins and spots are surrounded by a chlorotic halo. During summer 2012, two samples of 15 F-1 leaves were collected from spring barley cv. Maali and line SJ111609 from the Estonian Crop Research Institute in eastern Estonia in late July at growth stage 71 (4). In addition, six grain samples, containing 200 seeds each of the cv. Maali, were collected from different agricultural regions in Estonia, along with one grain sample of SJ111609 from Jõgeva. All samples were collected from untreated plots and leaves were observed under a dissecting microscope, revealing white clusters of conidiophores in rows on the undersides of the leaves. Conidia and conidiophores were scraped aseptically from the leaf surface using a sterile needle under a dissecting microscope and transferred to potato dextrose agar (PDA) containing ampicillin sodium salt (50 mg l−1). Plates were incubated at 18°C in the dark for 20 days until fungal mycelia were produced. The fungus was initially identified as Rcc on the basis of morphological characteristics (3). Colorless, 0- to 3-septate conidiophores were 15 to 17 × 2 to 5 μm, with a strongly curved end. Conidia were 7 to 11 × 3 to 6 μm, solitary, subglobose, single-celled, and of a darkish color. To confirm the presence of Rcc, DNA was extracted from the original barley leaf material, milled seeds, and positive control mycelia of Rcc grown on PDA using DNeasy Plant Mini Kit (Qiagen Gmbh, D-40724 Hilden, Germany) following manufacturer's guides. Rcc specific primers RC3 and RC5 (1) were used. A positive control consisting of 1 ng of purified Rcc DNA was included in the PCR. Standard PCR was conducted in a SEE AMP Seegene cycler. PCR were carried out in 20 μl volumes, containing 2 μl of DNA, 10 μl PCR mix, 0.4 μl each of forward and reverse Rcc primers, and 7.2 μl H2O. Qualitative detection analyzed by standard PCR with primers RC3 and RC5 revealed the presence of Rcc in symptomatic leaves and seeds. To complete Koch's postulates, a pathogenicity test was performed. Twenty-five barley seedlings were grown under controlled conditions (15°C/48 h dark, 16 h light/8 h dark, 70% RH) and spray-inoculated with a suspension of Rcc mycelium fragments as described by Macepeace et al. (2). The pathogen was re-isolated from leaves with necrotic lesions similar to those observed in the field, thus fulfilling Koch's postulates. To our knowledge, this is the first confirmed report of Ramularia leaf spot caused by Ramularia collo-cygni on barley in Estonia. References: (1) P. Frei et al. J. Phytopathol. 155:281, 2007. (2) J. C. Makepeace et al. Plant Pathol. 57:991, 2008. (3) B. C. Sutton and J. M. Waller. Trans. Brit. Mycol. Soc. 90:55, 1988. (4) J. C. Zadoks et al. Weed Res. 14:415, 1974.