First report of Curvularia alcornii causing leaf spot of quinoa in Bangladesh

Abstract

Quinoa (Chenopodium quinoa Willd.) is a nutritionally valuable pseudo-cereal with growing cultivation potential in Bangladesh; however, its productivity is increasingly constrained by foliar diseases, particularly leaf spot. During field surveys at Sher-e-Bangla Agricultural University, Dhaka, quinoa plants exhibiting typical leaf spot symptoms were observed. The present study aimed to identify and characterize the causal agent using an integrated morphological, molecular, phylogenetic, and pathogenicity-based approach. A fungal isolate (SMM-CaQSAU-1) was consistently recovered from infected leaves. Morphological characterization on potato dextrose agar revealed grey to black colonies with abundant aerial mycelia and conidia that were ellipsoidal to curved, dark brown, thick-walled, measuring 18–22 × 8–12 µm. Molecular identification based on BLAST analysis showed that the isolate shared 91.70% sequence similarity in the internal transcribed spacer (ITS) region and 98.39% similarity in the large subunit (LSU) rRNA region with the Curvularia alcornii reference strain MFLUCC 10–0703. Phylogenetic analysis using concatenated ITS and LSU sequences placed the isolate within a well-supported C. alcornii clade, distinct from other Curvularia species. Pathogenicity tests on detached leaves and intact quinoa plants reproduced characteristic leaf spot symptoms within 3–5 days after inoculation, and the pathogen was successfully re-isolated, fulfilling Koch’s postulates. To our knowledge, this study represents the first report in Bangladesh of C. alcornii causing leaf spot disease in quinoa. The findings provide critical baseline information for accurate disease diagnosis and highlight a potential emerging threat to quinoa cultivation in Bangladesh, underscoring the need for surveillance, resistance screening, and integrated disease management strategies.