Photinia × fraseri is widely cultivated as an ornamental plant in gardens (Deng et al. 16 2024). Agricultural industrial park of yangtze university (133 hm²) in Jingzhou, Hubei, China, has P. × fraseri extensively planted along most roadsides. However, this plant is prone to diseases. In July 2025, approximately 15% of P. × fraseri in the farm’s greenhouse showed black necrotic leaf symptoms, reducing ornamental value and threatening local cultivation. This study thus focuses on identifying the pathogen and developing control strategies to support healthy P. × fraseri cultivation. To isolate the pathogen, symptomatic leaf segments (5 × 5 mm) were collected from diseased plants. The leaf tissues were surface-disinfected with 75% ethanol and 2% NaClO for 30 s, rinsed three times with sterile water, and then incubated on potato dextrose agar (PDA) medium supplemented with 50 µg/mL streptomycin. Plates were kept at 28 °C in the dark for 3 days. Three colonies with similar morphology were obtained, all exhibiting a cotton-like appearance, initially grayish-white and later turning dark gray, with black pigmentation on the reverse side. On oat agar medium, conidia of the isolates were solitary or arranged in chains, mostly ellipsoid to obclavate, light to dark brown, and relatively smooth-walled. The conidia typically had 3-5 transverse septa and 1-2 longitudinal septa, which were clearly visible. Conidial dimensions ranged from 16.73 to 49.06 µm (n = 30). These morphological traits are consistent with descriptions of Alternaria alternata species complex (Woudenberg et al. 2014). For molecular identification, the gene regions ITS, GAPDH, RPB2, TEF1, SSU, OPA10-2, and LSU were analyzed (Woudenberg et al. 2015). The resulting sequences were deposited in the GenBank database. BLAST analysis revealed 99 - 100% similarity with the corresponding sequences of A. platycodonis CBS 121348 (ITS: KP124367, GAPDH: KP124219, RPB2: KP124836, TEF1: KP125144, SSU: KP124990, OPA10-2: KP124679, LSU: KP124520). Phylogenetic analysis using bayesian Inference (BI) placed the isolate in the same clade as the ex-type strain A. platycodanis CBS 121348. Pathogenicity tests were conducted by spray-inoculating leaves of P. × fraseri with a conidial suspension (10⁶ spores/mL) obtained from a 15-day-old culture. Three replicates were maintained at 25 °C. Symptoms similar to those observed in the field developed 20 days after inoculation, while control leaves treated with sterile water remained symptomless. To fulfill Koch’s postulates, the pathogen was re-isolated from the inoculated leaves and confirmed to be identical to the original isolate based on morphological and molecular characteristics. Alternaria platycodanis is known as a plant pathogen causing diseases such as black spot decay in pears (Qu et al. 2025), as well as foliar blight, leaf spot, and stem blackening in Lallemantia iberica (Pouralibaba et al. 2024). To our knowledge, this is the first report of A. alternata causing leaf spot on Photinia × fraseri in China.
Pan et al. (Thu,) studied this question.