Brown leaf spot (leaf blight) is a fungal disease caused by Mamianiella coryli, causal agent of early defoliation in summer, and is widely distributed in hazelnut (Corylus avellana L.) growing regions of Iran. During 2019-2020, 48 native and foreign hazelnut cultivars/ and or genotypes were evaluated for susceptibility against M. coryli under natural infection conditions at Astara Horticultural Research Station (northern Iran). One hundred infected leaves were randomly collected from four geographical directions and middle of canopy of each hazelnut tree. Disease severity index (DSI%) on leaves was calculated based on 1-5 rating system (1= >0 to 20% leaf area affected and 5= >80% of leaf area affected) and levels of reactions were determined based on DSI% (<1%= Highly resistant and >50%= Highly susceptible). None of the hazelnut cultivars had genetic resistance to M. coryli and all of the genotypes were grouped into two categories included susceptible (25.1-50%) and highly susceptible. Seven cultivars and/or genotypes included Souchi, Gerdoii 89, Pashmineh 89, Rimsky, Segorbe, Dedobestani and Pronnes were high susceptible and the rest were in the susceptible categories. It was concluded that sanitation of leaf debris in the fall, pruning for better air circulation or fungicide applications in the spring might be useful in disease outbreak conditions. Manuscript profile

Hazelnut (Corylus avellana L.) is affected by dieback (DB) and decline (D) diseases causing significant losses to hazelnut production in the Eshkevarat (Guilan province, northern Iran) as the main region for hazelnut production in Iran. Although, causal agents of these disorders have remained uncertain for many years. During 2017-18, results of a survey on DB and D diseases in hazelnut -growing sites (HGS) from Roudsar (54 out of 199 villages) and Amlash (14 out of 124 villages) counties (Eastern Guilan) revealed that mean frequency distributions (%) of DB and D diseases based on the infected HGS in the Roudsar and Amlash counties were equal to 27.14 and 10.85%, respectively. DB and D diseases were widespread in the Eshkevarat region, where they occurred in 38.7 - 55.3% of the hazelnut orchards. Mean tree infection (%)ranged from 3.94 to 28.3% and 6.1 to 33.6% in Amlash and Roudsar counties, respectively. The fungi with different distribution frequencies includedCytospora sp. (33.60%), Phomopsis sp. (14.40%), Verticillium dahliae(11.20%), Lasiodiplodia sp. (16.80%), Rosellinia necatrix (10.40%), and Pestalotiopsis sp. (13.60%), which were isolated and identified based on their morphological and cultural characteristics and were tested for their pathogenicity. Fungal pathogens infected hazelnut trees individually, or in combinations, to cause hazelnut dieback. Most of these fungal pathogens initiate infections at wounds caused by insects, humans, machinery, lightning, wind, and hail. Manuscript profile

Hazelnut (Corylus avellana L.) production is well-established in Iran. Cultivars that are resistant to plant diseases are needed to expand hazelnut cultivation. The present research aimed to study and compare the susceptibility of 48 Iranian, local and exotic hazelnut cultivars (C. avellana L.) to Phyllactinia guttata, the pathogen causing powdery mildew (PM). The study was conducted under naturallyoccurringinfection at a Research stationforhazelnutin the Guilan province (Astara-north of Iran), during the period 2019-2020. Experiments were arranged in a randomized complete block design with four replicates. The studied cultivars were divided in classes of susceptibility toPh. guttatadepending on the leaf infection (%) and disease severity index (DSI), using a 8-rating scale (0= no visible leaf symptoms to 7 = more than 85% of the leaf surface with symptoms). None of the investigated cultivars demonstrated resistance. Although no plot was scored less than 4, highly significant differences (P=0.01) in susceptibility among hazelnut cultivars were found. So that, 75% of the hazelnut cultivars exhibited high susceptibility to PM. Nocorrespondence was observed within cultivars based on geographical origin. In general, Iranian superior local cultivars Gercheh, Pashmineh 89, Shast-e-Ras, Gerdoii 89 and four Spanish commercial cultivars Fertile de Coutard, Segorbe, Negret, and 'Rondedu Piedmont showed high susceptibility reaction to PM. It was recommended that while paying attention to the susceptibility of cultivars to PM, control measures should also be considered. Manuscript profile

Hazelnut (Corylus avellana L.), one of the world's major tree nut crops, is widely produced in Iran, with an annual yield of more than 21,500 tons of hazelnuts. A survey of hazelnut orchards in Iran was conducted during 2021-2022, revealing the presence of root tumors on hazelnut trees in Guilan (northern Iran), Mazandaran (northern Iran), Qazvin (northwestern Iran), and Qom (north-central Iran) provinces. Samples of these root tumors were collected for further analysis. Isolations from fresh galls on SNA, D1M, IA, LB, and SC culture media yielded predominant colonies similar to Agrobacterium, which were subsequently purified and characterized. All 29 strains isolated were Gram-negative, rod-shaped, obligate aerobic, motile, and tested positive for oxidase, catalase, arginine dihydrolase, and urease. However, they did not hydrolyze starch, gelatin, or esculin, but did hydrolyze Tween-80 and urea. They exhibited growth on 2% NaCl and at 35°C, and were able to produce 3-ketolactose but not indole, DNase, pectinase, levan, or reduce nitrate. Furthermore, 11 representative strains were randomly selected for PCR amplifications of T-DNA genes using specific primers At1/At2, F8360/F8361, and tms2F1/tms2R2, resulting in 338, 453, and 617 bp amplicons, respectively. In pathogenicity tests, bacterial strains were inoculated into tomato, hazelnut, sunflower seedlings, and carrot discs, leading to the formation of tumors on plant stems and callus on carrot discs. Based on phenotypic, physiological, and biochemical properties, pathogenicity tests, and molecular methods, the bacterium responsible for causing root gall in hazelnut trees was identified as A. tumefaciens biovar 1. This bacterial root gall appears to be widespread among various local hazelnut cultivars (Gerd-e-Eshkavar, Alamout, Tarom, etc.), with a higher prevalence in old hazelnut orchards with stony soils. This study represents the first report of root gall on hazelnut trees grown in Iran. It was observed that the number of sites where tumors have developed and the number of galls present in old hazelnut orchards with stony soils are higher. Manuscript profile

Iran has suitable conditions for cultivating high-quality varieties of hazelnuts (Corylus avellana L.). Most of hazelnut orchards in Iran have been established by planting native genotypes. Aspergillus flavus Link. (AF) is a filamentous fungus affecting hazelnut kernels in orchards and during storage conditions. The most widely explored strategy for reducing aflatoxin contamination is the development of host resistance. The relative susceptibility of 12 native and exogenic hazelnut varieties including Soorii, Gerd-e-Eshkevarat, Gerd-e-Shouk, Navan 1, Fertil du Cortard, Pashmineh 89, Rasmi, Gerje, Ronde du pimount, Shastak, Negret, Gerdooii, to AF contamination was evaluated as in vitro by the kernel screening assay. Hazelnut kernels were surface sterilized and then inoculated with spore suspension (1×106 spores/ml) of AF by dipping method. Experiments were done in a completely randomized design with four replications. After five days of inoculation and incubation at 28 °C, the criteria of the AF growth (sporulation density, SD %) and sporulation rate (SR, spores/ml) on whole (intact) and wounded (cut) kernels of hazelnuts were measured. Results revealed statistical significant differences among hazelnut varieties for the SD% and SR parameters (ρ≤0.05). The Averages SD% and SR of A. flavus on intact and wounded kernels ranged from 16.50-75.14%, 48.25-100% and 14.6×105-16.7×106, 12.6×107-47.6×107, respectively. The highest and lowest SD% on whole and wounded kernels was related to hazelnut varieties Pashmeneh 89 and Gerde-Eshkevarat, respectively. The cultivated variety Gerde-Eshkevarat was recorded as an important potential source of resistance to AF. Manuscript profile