In July 2023, chestnut tree mortalities were reported in the parc châtaigneraie, situated in the Akfadou mountain range, in Tizi Ouzou, Algeria. Dead sweet chestnut (Castanea sativa) trees exhibited symptoms including crown dieback, withered and dried leaves clinging to the branches, and trunk and branch cracks and cankers, with a proliferation of epicormic shoots under the cankered areas. 

Examination of the cankers with a handheld magnifying lens exposed orange masses, erupting from under the bark. Cankers were found on the lower part of the trunk, with few occurrences on the branches. Flat mycelial fans were observed throughout the bark. Samples of infected wood were collected and subjected to further analysis in the laboratory. Close observation of fragments of infected wood under the stereomicroscope showed orange to dark orange fruiting structures (pycnidia), originating in the cambium, which showed a discoloration in cross section. After incubation (24 h) in a humid chamber, twisted yellowish tendrils oozing from the pycnidia were observed. Pycnidia were isolated from the bark and transferred onto full-strength potato dextrose agar (PDA). Fast-growing whitish colonies that turned yellow-orange developed within 5 days, with a growth rate of 7 mm/day at 30°C. Conidiospores were hyaline, aseptate, oblong to cylindrical, and 2 to 4 × 1.5 to 2 μm in size. Total genomic DNA was extracted, and the elongation factor 1-alpha (EF-1α) (Carbone and Kohn 1999) and beta-tubulin (βT1) (Glass and Donaldson 1995) gene regions were amplified using the Phire Direct PCR Kit (Thermo Fisher). PCR amplicons were subsequently sequenced. The EF-1α (PQ416673) and βT1 (PQ416670) sequence identity was determined using the GenBank database with 99.69 and 100% identity to Cryphonectria parasitica (OM112254.1 and MK578073.1), respectively. Based on disease symptoms, cultural and morphological characteristics, and DNA sequence similarity, the fungal pathogen was identified as C. parasitica. Koch’s postulates were performed to confirm the pathogenicity of C. parasitica by using detached twigs of chestnut trees as described in Hunter et al. (2013). Twelve chestnut twigs (20 cm long and 2 cm in diameter) were surface sterilized and then put to dry in a laminar hood under a constant airflow for 10 min. Seven-day-old mycelial plugs from cultures of C. parasitica were used to inoculate two branches with three replicates. The six controls were inoculated with PDA plugs. After 5 weeks of incubation at 20°C (9-/15-h light/dark regime, respectively), canker zones developed around the inoculation point, from which the pathogen was reisolated. The recovered C. parasitica isolate was confirmed using methods described above. The resulting consensus sequences of the recovered pathogen matched C. parasitica with 99.71 to 100% identity to EF-1α (PQ416674 and PQ416675) and 100% identity to βT1 (PQ416671 and PQ416672). This represents the first report of C. parasitica in Algeria and the second report in Africa (EPPO 1994). According to forestry archives, the chestnut groves of Tizi Ouzou infected with C. parasitica came from the Cévennes in France (Rabhi and Messaoudène 2018). Further field surveys need to be conducted to detect the presence of this disease in other chestnut orchards across Algeria, and phytosanitary regulation measures must be undertaken in order to counter the spread of this disease in Algeria and the North African region.