The interest in hazelnut (Corylus spp.) cultivation in Bulgaria has vastly increased. In the northern part of the Plovdiv district at the end of 2015, hazelnut kernels with necrotic and sloughing off pellicle and sunken surface lesions under visibly healthy shells were observed. Kernels with the same symptoms were also found in the autumn of 2016 on the most widely distributed cultivars Tonda Romana (C. avellana), Almond Shaped (C. maxima) and Early Trapesund (C. maxima) from private yards and orchards up to 80 km from the first locality. Symptomatic kernels with removed skin were used for isolations on potato dextrose agar (PDA, Biolife, Italy) and subsequent incubations for 4-5 days at 25°C revealed yeast-like, white to slightly creamy, butyrous colonies with raised centers and peripheral mycelial fringes. In addition to septate mycelium, microscopic observations (total number of 50 for each following structure) also revealed the presence of globose budding cells (diameter of 7 to 26 μm) and cylindrical...

Field surveys in the region of Plovdiv within a small mixed orchard of peach and nectarine trees in the summer of 2017 revealed symptoms and signs of brown rot attended by numerous, slightly greyis...

In June 2020, during an observation of fruit-bearing hazelnut trees (Corylus avelana L., cv. Tonda Gentile), grown in a small private home garden in the region of Kavarna (North-Eastern Black Sea coast of Bulgaria), symptoms of powdery mildew were observed on each of the 15 trees. Compared to the widely spread in Bulgaria powdery mildew caused by Phyllactinia guttata and known with its powdery patches and differing chasmothecia exclusively formed on the abaxial leaf surface, the newly observed disease was characterized by the presence of concomitant pathogen's structures on both the abaxial and adaxial surfaces of the leaves, varying from single pustules to 90% severity on certain leaves, as well as on the husks which were 100% affected. Among the white mycelium, cylindrical conidiophores and singly produced conidia (22-34 x 16-22 µm; n = 50) were found. Scattered or in groups, black spherical chasmothecia (diameter of 85-115 µm; n = 30), possessing 8 to 12 appendages with dichotomous branched apices, were also observed in the autumn. Chasmothecia contained 3 to 5 subglobose asci (45-60 x 34-62 µm; n = 30), each ascus containing 8 hyaline and ellipsoid ascospores (15-22 x 9-16 µm; n = 50). From one field powdery mildew sample DNA was extracted using the Nucleospin Plant II kit (Macherey-Nagel, Germany) and the rDNA ITS region was amplified using primers PMITS1 and PMITS2 (Cunnington, J.H. et al., 2003). The amplicon was sequenced (Macrogen Europe, The Netherlands) and used in a BLAST analysis. This resulted in 100% homology with the ITS sequence of Erysiphe corylacearum. The obtained sequence was different from the ones of Erysiphe pseudocorylacearum (99.20% homology) and Erysiphe coryli-americanae (96.52% homology). The targeted sequence was submitted to GenBank (accession number OQ860748). Based on the symptoms, morphological characteristics and molecular identification, the pathogen was identified as Erysiphe corylacearum. Pathogenicity of the fungus was confirmed under lab conditions (natural day/light regime, 23-25°C) by shaking down conidia from naturally infected leaves on both sides of healthy leaves (2-years plantlets, cv. Tonda Gentile, 3 replicates) and incubation in a moist chamber (plastic bags) for the first 24 hours. First small fluffy white pustules appeared 6-7 days after inoculation, subsequently, the disease was progressing and the pathogen's conidiophores and conidia were morphologically identical to that first observed under natural infections in the private garden. The non-inoculated control plantlets (grown under the same conditions in a separate room) remained symptomless during the entire three weeks testing period. To our knowledge, this is the first report of Erysiphe corylacearum on hazelnut in Bulgaria. In October 2021, the same disease was also found in a hazelnut orchard (1.2 ha) located in the region of Pazardzhik (Central Southern part of the country). Globally, this report indicates the disease's expansion in the Black Sea region since its first observation in Turkey in 2013 (Sezer, A., et al. 2017; Heluta, V.P., et al. 2019; Meparishvili, G., et al. 2019; Rosati, M., et al. 2021) and elsewhere in Europe as well (Beenken, L., et al. 2020; Mezzalama, M., et al. 2021; Voglmayr, H., et al. 2021).

Sunflower (Helianthus annuus) is widely used for cut flowers and decoration in Belgium. A serious outbreak of what was suspected to be white rust on sunflower was observed in an East Flemish nursery near the city of Ghent in August 2004. This disease has previously been reported in Europe (southwest of France) (1) and other parts of the world with losses as much as 70 to 80% (Australia, North and South America, and Africa) (2,3). In the Flemish nursery, only single diseased plants (cv. Sunrich) were found. Blister-like pustules containing sporangia were observed on infected leaves. Initially the blisters were pale green to yellow on the abaxial surface and white on the adaxial surface of the leaves. As the disease progressed, white pustules that formed on the adaxial surface of the leaves slowly turned yellow, and the blisters on the abaxial surface became yellow to orange and necrotic in the center. Finally, the pustules coalesced and the leaves withered. Stem lesions were not observed. Short, cylindrical to spherical-cuboid sporangia, recovered from the pustules on the adaxial surface of leaves, measured between 17.5 and 22.5 μm, with an average of 20.2 μm. Sporangial dimensions were similar to those of Albugo tragopogonis (Pers.) S.F. Gray (1). Inoculations were done by spraying a suspension of 1 × 10⁵ sporangia per ml prepared by scraping pustules from naturally infected leaves. Leaves on three 2-month-old healthy plants were sprayed with this inoculum and three plants sprayed with distilled water served as controls. The plants were kept for 48 h under a humid chamber and subsequently at room temperature (20 to 25°C) on the laboratory bench. Initial symptoms of white rust were observed 12 to 14 days after inoculation. On the basis of symptoms, morphological characteristics, and pathogenicity tests, the pathogen was identified as A. tragopogonis. To our knowledge, this is the first record of A. tragopogonis on H. annuus in Belgium. References: (1) K. G. Mukerji. Description of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, England, UK, 1976. (2) A. Pernaud and A. Perny, Phytoma 471:43, 1995. (3) P. S. van Wyk et al. Helia 22:83, 1999.

Maize (Zea mays) is the second most grown cereal crop in Bulgaria with an average area of about 500 000 ha. Damage was observed in October 2014 on a plot in the region of Silistra (North-Eastern Bulgaria). Symptoms consisted of scattered plants with suppressed growth and small cobs due to a root and stem base rot. On some of the damaged parts (except cobs) black conidiomata were visible. The isolations on potato dextrose agar (PDA) revealed a relatively fast growing fungus. The single-conidia colonies grown in the dark at 25°C on PDA were fluffy and covered the plates (d = 90 mm) in about one week. The conidiomata both on plant parts and medium released two types of conidia morphologically identical to those of Phaeocytostroma ambiguum (Mont.) Petr. (Lamprecht et al. 2011). The predominant type (alpha-conidia) were pale to medium brown, ellipsoid to pyriform, with an ovoid to truncate base, averaged 13.8 x 6.8 μm. The second type (beta-conidia) were sparse, predominantly formed in conidiomata on plant tissue, and were pale brown, subcylindrical, straight to curved and measured 15-28 x 1.25-2 μm. Pathogenicity of two isolates was proven by artificial inoculation of maize seedlings (4-week old, 3 plants per pot, d = 10 cm) by pouring the substrate with a mix of sterile water (100 ml) and a blended 3-week old colony grown on PDA, followed by incubation in a moist chamber (72 hrs). Additionally, detached maize cobs (milk and dough stages) were also inoculated by placing colonized PDA plugs (5 mm) under the corn-husks and covering the inoculation site with plastic tape before incubation under moist conditions (48 hrs). All inoculated objects and the negative controls (inoculated with sterile water or sterile PDA plugs) were incubated at room temperature (22-25°C). A positive reaction consisting of necrosis around the inoculation point was first found on the cobs after one week. After another 2-week period the symptomatic zone enlarged and was covered by numerous emerging small black stromata. The single-necked conidiomata were fully mature after about 40 days. Symptoms of wilting and root necrosis were registered in the seedlings test about a month after the inoculation. The subsequent re-isolations revealed the same fungus from all inoculated samples but not from negative controls. The genomic DNA of one isolate was extracted using a fast DNA extraction method (Vercauteren et al. 2010). The rDNA-ITS region was amplified using primers ITS1 and ITS4 (White et al. 1990) and the PCR product was sequenced. This sequence was used in a BLAST search on NCBI, resulting in a 100% homology to all Phaeocytostroma ambiguum ITS sequences present in the database, and was subsequently submitted to GenBank (accession number KT966745). To our knowledge, this is the first report of Phaeocytostroma ambiguum (Mont.) Petr. as the causing agent of root and stem base rot on maize in Bulgaria and the pathogen’s capacity also to inoculate the cobs is a warning to the growers about potential complications resulting from the disease.

Expansion of hazelnut (Corylus spp.) cultivation in Bulgaria has led to an increased interest in any attendant disease. In the district of Plovdiv during the post-harvest storage periods of 2015 and 2016 shriveled nuts of the cultivars Tonda Romana (C. avellana) and Early Trapesund (C. maxima) were observed. Nuts originating in three locations displayed necrotic pellicles and sunken moldy surface lesions followed by dry rot. Microscopic observations revealed the presence of septate, dichotomously branched and undulating mycelium, and of hyaline, solitary, terminal and fusiform asci that had a rostrum-like apical appendage. Asci 41.6 (40.0-43.3) x 15.4 (11.7-18.3) μm, n=50, usually contained eight uninucleate, slightly bent, wedge-shaped, elongate with one end obtuse and the other end gradually attenuating into a fine point, hyaline ascospores sized 17.6 (16.6-18.3) x 3.0 (2.5-3.3) μm, n=50. Symptomatic pellicles and seeds were plated on potato dextrose agar (PDA), and incubation at 25°C resulted in slow-g...