Pathogenic Alternaria Species Associated with Young Cedrus atlantica Manetti: Morphological and Molecular Characterization

The seedlings of the young Atlas cedar (Cedrus atlantica Manetti) are very important for the regeneration and restoration of forest populations of this endemic species, which inhabits a very fragmented area in the highest mountains of North Africa (Algeria and Morocco). There is very minimal information on the diseases that are afflicting these young plants. In this work, Alternaria strains CHP2, S4.2, and SP1.1 were isolated from different plants and subjected to identification and pathogenicity testing. The infected plants developed clear symptoms of light brown disease spots on the leaves with a yellowish or chlorotic halo around them, which gradually developed to a yellowing of the plantlets and their complete drying. Some spots merged to form large areas of necrosis which covered an average of 80% of the plantlets. The impact of the infection on plant physiology was determined using measurements of photosynthetic pigments, which showed reductions of 46.28% in chlorophyll and 59.90% in carotenoids in strains SP1.1 and CHP2, respectively. Molecular characterization of the ITS region of the isolates revealed that strains CHP2 and S4.2 showed high sequence similarity to reference sequences of Alternaria spp., including taxa related to A. destruens and A. murispora, although species-level identification remains tentative. These findings highlight the growing relevance of fungal pathogens in forest regeneration under global climate change. By revealing the pathogenic role of Alternaria species, this study contributes to sustainable forest management and conservation strategies in changing environments.