First Report of <i>Pyracantha fortuneana</i> Fruit Rot Caused by <i>Alternaria alternata</i> in Yunnan Province, China

Pyracantha fortuneana (H. L. Li, Rosaceae), valued for ornamental and ecological uses, is widely distributed in southern/southwestern China. Its polysaccharides exhibit antioxidant and anticancer potential, driving commercial juice development (Yao et al. 2020). On 10 October 2024, fruit rot symptoms were observed on P. fortuneana at Qujing Normal University, Yunnan, China (25.52°N, 103.75°E). Symptomatic fruits displayed circular to subcircular black lesions; internal tissues were necrotic and brown. Disease incidence averaged 10.4% ± 2.07% (SD) across 500 fruits from five replicates (100 fruits each). Pathogen isolation utilized four replicate 9-cm PDA plates. Three lesion-margin fragments (0.2 × 0.5 cm) per replicate were surface-sterilized (75% ethanol, 4 min), triple-rinsed in sterile water, and incubated at 28 °C in darkness. Hyphal tips from emerging white mycelia were transferred to PDA medium plate after 24 h. Colonies developed gray-green centers with regular white margins within 3 days, covering plates fully by day 9. Nine morphologically similar strains were isolated; a representative (BHB) was characterized morphologically and molecularly. After 14 days, colonies produced solitary or catenate conidia (5.28–13.52 μm × 8.90–28.38 μm; mean 8.66 × 15.50 μm, n=50). Conidia were pyriform to elliptical, with 1–6 transverse and 0–1 longitudinal septa, exhibiting slight septal constrictions, consistent with Alternaria spp. (Simmons 2007). For molecular identification, genomic DNA was extracted, and eight loci were amplified/sequenced: SSU (NS1/NS4), LSU (LSU1Fd/LR5), ITS (ITS1/ITS4), TEF1 (EF1-728F/EF1-986R), Alt a 1 (Alt-for/Alt-rev), EndoPG (PG3/PG2b), OPA10-2 (OPA10-2R/OPA10-2L), H3 (H3-1a/H3-1b) (Zhang et al. 2023; Zheng et al. 2015). Sequences (SSU: PQ895780; LSU: PQ895777; ITS: PQ895770; TEF1: PV082022; Alt a 1: PV082020; EndoPG: PV092677; OPA10-2: PV092678; H3: PV082021) showed 95–100% homology to Alternaria alternata reference strains (GenBank accessions: PP190241 [1,010/1,010 bp], PP190242 [858/858 bp], PP189927 [544/544 bp], PP196558 [251/252 bp], PP196559 [462/481 bp], PP196560 [439/439 bp], PP196561 [670/702 bp], ON375577 [407/407 bp]). Maximum-likelihood and Bayesian phylogenetic analyses (PhyloSuite v1.2.3) using concatenated loci placed BHB within the A. alternata clade. Combined morphology and multigene phylogeny identified BHB as A. alternata. Pathogenicity was confirmed by inoculating needle-wounded fruits with mycelial plugs and conidial suspensions (1×10⁶ conidia/ml). Unwounded fruits inoculated with suspensions/plugs served as positive controls; needle-wounded fruits treated with sterile water were negative controls. After 7 days, lesions matching field symptoms developed on all plug-inoculated fruits (wounded/unwounded), but only on wounded suspension-inoculated fruits. Negative controls remained symptom-free. Reisolation from lesions yielded cultures morphologically and molecularly identical to A. alternata. To our knowledge, this is the first report of A. alternata causing P. fortuneana fruit rot in China. These findings provide critical insights for monitoring disease spread and developing control strategies.