Morphological and Molecular Characterization of Nigrospora oryzae Causing Leaf Blight and Wilt in Oreopanax...

The genus Nigrospora remains poorly understood as a plant pathogen. Until 2026, there were only 26 species recorded in MycoBank and 19 in GenBank. Diseases caused by Nigrospora were once considered uncommon, but in recent years there has been a sharp rise in first reports globally, especially in tropical and subtropical regions such as China, Malaysia, India, and the Americas, as well as in Europe. In November 2022, Oreopanax ecuadorensis, a plant endemic to Ecuador, exhibited symptoms of leaf blight and wilting in Quito Metropolitan Park-South, Ecuador. The causal agent was isolated on PDA; DNA was extracted, and PCR products of the ITS and EF regions were sequenced. DNA sequences from isolate CBC-FCA-001 were deposited in GenBank under accession numbers OR597663.1 (ITS region) and PP897887.1 (EF region). Morphological and molecular analyses identified the causal agent as Nigrospora oryzae. Koch's postulates confirmed the isolate's pathogenicity, with mycelium-inoculated, non-wounded plants exhibiting characteristic symptoms while control plants remained healthy. This marks the first report of N. oryzae affecting O. ecuadorensis. Symptoms were observed on multiple plants throughout the site, raising concerns about the vulnerability of endemic flora to emerging pathogens. The rise in Nigrospora-associated diseases, potentially driven by climate change and human activities, highlights the urgent need for research to mitigate their impacts on agriculture and biodiversity conservation.