First occurrence of Corynespora cassiicola infecting chia plant in Bangladesh and sensitivity of the pathogen to selected fungicides.

Abstract

Chia (Salvia hispanica L.) is an emerging crop in Bangladesh valued for its medicinal properties and economic significance. In March 2024, target spot-like symptoms were observed in an experimental chia field (24.75° N, 90.50° E) at Bangladesh Agricultural University in Mymensingh, Bangladesh, with disease incidence ranged from 23% to 47% across approximately 0.25 ha. Initially appearing as brick-red spots, these symptoms developed into target-shaped concentric rings, affecting leaves, stems, and inflorescences. A total of 24 fungal isolates were recovered from infected tissue; two representative isolates (BGECh-3 and BGECh-4) were randomly selected for detailed characterization. Pathogen identity was established through morphological traits, multilocus phylogenetic analysis of internal transcribed spacer (ITS) and elongation factor 1-alpha (TEF-1α) gene sequences identifying the causal agent as Corynespora cassiicola. Pathogenicity was confirmation through Koch's postulates, and the isolates demonstrated a broad host range and were pathogenic to brinjal, chili, bottle gourd, country bean, tomato, and soybean. In vitro fungicide sensitivity assays with seven commercial fungicides showed that both isolates were highly sensitive to Goldazim (50% carbendazim), which caused 98.05 ± 2.88% mycelial growth inhibition at 10 µg mL - ¹ and complete inhibition at higher concentrations, with the lowest EC50 (0.76 µg mL - ¹). Conza (10% Hexaconazole) and Amistar top (18.2% azoxystrobin + 11.4% difenoconazole) also exhibited high efficacy, achieving 86.17 ± 1.31% and 67.77 ± 1.34% inhibition, respectively, at the same concentration, with EC50 values of 1.34 and 1.09 µg mL - ¹, respectively. Tilt (25% propiconazole) showed moderate activity (59.30 ± 2.08% inhibition at 10 µg mL - ¹; EC50 = 4.75 µg mL - ¹), whereas the remaining fungicides exhibited comparatively lower efficacy and did not produce reliable EC50 estimates. This study represents the first report of target spot disease of chia caused by C. cassiicola in Bangladesh and provides insights for effective disease management strategies.