First Report of needle blight Caused by Darkera parca on Picea schrenkiana Fisch. et Mey. in Xinjiang, China

Picea schrenkiana Fisch. et Mey., a keystone species for maintaining the ecological balance of the desert-oasis ecosystem in the Tianshan Mountains (Huo et al. 2017), was observed with severe needle blight symptoms in a natural stand (≈20 ha) in Tacheng, Xinjiang, China (44°10′48″ N, 84°7′35″ E; altitude 1681 m) in May 2025. Disease incidence ranged from 25% to 35% across five standard plots (100 trees/plot), with severely infected trees exhibiting yellowed crowns and reduced vigor. Affected needles showed longitudinally arranged black elliptical lesions (200-300 µm diameter) embedded under the epidermis. As the disease progressed, needles turned brown but remained attached to living twigs. Twenty symptomatic needles collected from 10 trees were surface-sterilized (75% ethanol, 1 min; 1% Ca(ClO)2, 40 s), and conidiomata were excised, transferred to potato dextrose agar (PDA), and incubated at 25 ± 2°C. Twenty morphologically similar isolates were obtained via hyphal tip method, and two isolates (YS-2, YS-3) were selected for morphological and molecular characterization. Colonies were white, irregular, with floccose aerial mycelia and slow growth. Conidiomata were solitary or aggregated, immersed, globose to subovoid, unilocular, glabrous, 250-380 µm in diameter. Conidia (20.1-31.4 × 5.5-8.6 µm) were hyaline, subcylindrical, straight or slightly curved, truncate at the base, aseptate, smooth-walled, with irregular mucoid appendages. These morphological characteristics aligned with descriptions of the genus Darkera (Li et al. 2020). Genomic DNA was extracted from 15-day-old mycelia using a fungal genomic DNA extraction kit (Biomiga, USA). The internal transcribed spacer (ITS) region, translation elongation factor 1-alpha (TEF-1α), and 18S ribosomal RNA (SSU) regions were amplified with primers ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R (Carbone et al. 1999), and NS1/NS4 (White et al. 1990), respectively. Sequences were deposited in GenBank (ITS: PX642403, PX998304; TEF-1α: PX620502, PZ011831; SSU: PX642404, PX998305). BLASTn analysis of the sequences revealed 98.7% (409/412 bp) and 99.81% (527/528 bp) identity for isolates YS-2 and YS-3, respectively, with Darkera parca CPC23903 (KM108354.1) based on the ITS region; 100% identity (227/227 bp and 297/297 bp) with D. parca CPC23904 (KM108408.1) and D. parca CPC23903 (KM108407.1) based on the TEF-1α region; and 99.57% (468/470 bp) and 100% (473/473 bp) identity with D. parca CPC23903 (KM108354.1) based on the SSU region. A maximum-likelihood phylogenetic analysis based on concatenated ITS, TEF-1α, and SSU sequences grouped the isolates within the D. parca clade with 100% bootstrap support. Pathogenicity was confirmed on twenty 5-year-old healthy P. schrenkiana seedlings using a conidial suspension (1×106 conidia/ml), with sterile water as control. Inoculated needles were bagged for 48 h and maintained at 25°C. After 40 days, 80% of inoculated plants developed symptoms consistent with field observations, while controls remained asymptomatic. The same pathogen (reisolated as YS-X) was identified as D. parca, fulfilling Koch’s postulates. To our knowledge, this is the first report of D. parca causing needle blight on P. schrenkiana in Xinjiang, China. The pathogen contributes to tree decline and poses a threat to the ecological stability of the Tianshan Mountains, underscoring the need for early detection and management strategies.