First report of Colletotrichum nymphaeae causing anthracnose on argan (Argania spinosa. L) in Morocco

Abstract

This study presents the identification of Colletotrichum nymphaeae for the first time as the causal agent of anthracnose on argan fruits (Argania spinosa L.) in Morocco. The affected fruits were collected from Dar Chef Province (Ouazzane region). The pathogen was isolated and identified using morphological and molecular characterization. The pathogenicity tests were also carried out to confirm its ability to induce disease symptoms on argan fruits. The results showed fungal colonies that produce abundant orange conidial masses. The microscopic examination showed cylindrical, hyaline, unicellular conidia similar with known morphology of C. nymphaeae. Pathogenicity tests confirmed Koch’s postulates. The typical anthracnose symptoms were developed on inoculated fruits, with larger lesions developing on wounded tissues (average diameter: 1.64 cm) compared to unwounded tissues (0.66 cm). However, control fruits were asymptomatic. Molecular identification using the internal transcribed spacer (ITS) region of rDNA showed 99.83% similarity with C. nymphaeae isolate from China (GenBank: ON793164.1). Phylogenetic analysis grouped the Moroccan isolate (OP363901) within a well-supported clade alongside Asian and Central American C. nymphaeae species complex, confirming its taxonomic status within the C. acutatum species and highlights its genetic divergence from related species such as C. acutatum, C. lupini, and C. godetiae. This finding raises an important phytopathological concern, given the economic importance of argan oil production in Morocco. The wide host diversity and environmental adaptability of C. nymphaeae suggest its potential impact as an exotic threat to argan agroecosystems. The study highlights the urgent need for integrated disease management strategies and subsequent future research including multilocus sequencing in order to better understand the population structure and epidemiology of C. nymphaeae in Morocco.