Morphological Characterization and Pathogenicity Screening of Fusarium Isolates Associated with Dry Rot of Stored Potato Tubers in Mascara, Algeria

Potato (Solanum tuberosum L.) tuber dry rot caused by Fusarium spp. is a major postharvest disease responsible for significant storage losses worldwide. This study investigated Fusarium isolates recovered from symptomatic potato tubers collected in February 2025 from storage facilities in the Mascara region of Algeria. To our knowledge, this is the first regional characterization of Fusarium-associated dry rot in stored potato tubers from Mascara, Algeria. By integrating morphological characterization, quantitative pathogenicity assessment, and targeted molecular identification, the study examined the relationship between morphotype occurrence and disease-causing potential. A total of 118 purified Fusarium isolates were obtained from symptomatic potato tubers and grouped into 28 morphotypes based on cultural and morphological characteristics. One representative isolate from each morphotype was evaluated for pathogenicity on potato tubers of cv. ‘Arizona’ under controlled incubation conditions, and disease severity was quantified by image analysis. Of the 28 representative isolates tested, 15 induced dry rot symptoms, with marked differences in aggressiveness, whereas several isolates induced little or no necrosis under the conditions tested. Selected aggressive isolates were further analyzed using TEF1-α sequencing, which identified F14 as F. sambucinum and F171 as F. redolens, while F4 and F34 were identified to the F. oxysporum and F. solani species-complex level, respectively. Importantly, morphotype frequency did not necessarily reflect disease severity, as some of the most aggressive isolates belonged to less common morphotypes. These findings suggest that isolation frequency alone may not adequately reflect pathogenic importance and support the integration of occurrence data, pathogenicity testing, and molecular identification in the assessment of Fusarium-associated dry rot in potato storage systems.