Molecular Characterization of Phosphate Solubilizing Fungi Aspergillus niger and Penicillium expansum using the Species-Specific PCR Based Molecular Markers

Phosphorus (P) is a vital macronutrient, yet most soil P occurs in insoluble forms, driving intensive use of chemical fertilizers. Phosphate-solubilizing fungi (PSF), including Aspergillus niger and Penicillium expansum, can enhance P availability but also comprise important postharvest pathogens. This study aimed to characterize apple-associated isolates of both species using morphology and species-specific PCR based markers to provide a basis for future functional screening. A total of 126 fungal isolates (98 putative P. expansum, 28 putative A. niger) were cultured on PDA for macro- and micromorphological assessment and subjected to CTAB-based DNA extraction and PCR with species-specific primers. A. niger formed rapidly growing, granular powdery colonies that darkened to brown–black, with spherical vesicles densely covered by biseriate phialides and rough-walled, dark globose conidia in chains. P. expansum produced moderately fast, velvety colonies that shifted from white to blue–green with concentric rings and showed typical brush-like penicilli with terverticillate branching and smooth, spherical conidia. PCR amplification yielded the expected 404 bp product in 95/98 P. expansum isolates (96.93%) and the 197 bp product in 24/28 A. niger isolates (85.71%), indicating strong concordance between morphological and molecular identification. The integrated morphological-molecular approach reliably resolved apple-associated A. niger and P. expansum populations and establishes a validated genetic resource. Future work will couple PCR-based genotyping with phosphate-solubilization assays and pathogenicity tests to identify elite biofertilizer candidates while monitoring and managing high-risk postharvest lineages.