First report of needle blight of blue spruce (Picea pungens) caused by Neoscytalidium dimidiatum in Turkey

Abstract

The blue spruce (Picea pungens Engelm.) is an exotic conifer species widely used for decorative purposes in landscaping and private gardens. In 2020, 60% of forty blue spruce trees between 20 and 25 years old planted in front of buildings in Kavaklıdere, Ankara, displayed needle blight symptoms. Needles on the lower and interior crown closest to the trunk were infected from the bottoms of branches. They showed a brown-colored or burned appearance before dropping off, starting from their tips, resulting in up to a 65% reduction of the canopy. On the surface of infected tissues, a black-colored fungal mass was observed. Fungal colonies isolated from twenty symptomatic branches and needles were initially dark gray and became black within 4 to 7 days. Zero- to one-septate dark brown conidia (4.6 to 9.8 × 3.6 to 7.5 μm) formed in arthric chains were disarticulating and cylindrical-truncate to rod-shaped, oblong, ellipsoidal, doliiform, or globose, consistent with the description of Neoscytalidium spp. (Crous et al. 2006). The internal transcribed spacer, translation elongation factor 1-α, and β-tubulin loci of a randomly selected isolate (Nd_Pp01) were sequenced using the primers ITS1/4, EF1-728 F/986R, and Bt2a/Bt2b and deposited in GenBank under the accession numbers OK643641, OK666381, and OK666382, respectively. The sequences had 99.77–100% nucleotide identity with those of the type specimen of N. dimidiatum, CBS 145.78. Phylogenetic analysis with concatenated sequences further confirmed the identification. The isolate was deposited in the Bolu Abant Izzet Baysal University Culture Collection with accession number BAIBU-179. A pathogenicity test was conducted with ten 1-year-old P. pungens plants by spraying a conidial suspension (105 conidia/ml) of the isolate Nd_Pp01 onto the needles (Türkölmez et al. 2019). Five seedlings sprayed with sterile water were used as controls. All plants were placed in a growth chamber at 28°C with 70% RH. Spray-inoculated needles initially showed yellow spots within two weeks and turned brown six weeks after inoculation, whereas the controls remained symptom-free. The pathogen was re-isolated from the inoculated needles but not from controls. To our knowledge, this is the first report of N. dimidiatum causing needle blight on P. pungens in Turkey and worldwide (Farr and Rossman 2023).