Phylogenetic and Morphological Characterization of Spegazzinia Species from Oryza sativa L. in Thailand

Spegazzinia, a genus within the family Didymosphaeriaceae, is known for its pleomorphic conidia and diverse ecological roles. As a vital cereal crop, rice (Oryza sativa L.) supports a rich fungal community, yet many associated fungi lack thorough taxonomic validation combining morphology and molecular data. This study identifies and characterizes Spegazzinia species associated with rice in Thailand by collecting dead rice leaves in Chiang Rai Province. Fungal isolates were obtained through single-spore isolation, and their morphological traits were examined. Phylogenetic analyses were conducted using concatenated sequences from four gene regions, including large subunit nuclear rDNA (LSU), internal transcribed spacer (ITS), small subunit nuclear rDNA (SSU), and translation elongation factor 1-alpha (tef1-α). Maximum likelihood and Bayesian inference phylogenetic trees indicated that two isolates clustered with Spegazzinia deightonii and S. tessarthra. Morphological traits aligned with these species, including the production of two conidial types (α and β) with distinctive structural features. The isolate of S. tessarthra represents a new host record for Spegazzinia on rice, broadening its known host spectrum, while S. deightonii, first reported in 1971, is herein recollected on rice in this study. This research emphasizes the significance of integrating morphological and molecular approaches in fungal taxonomy, enhancing our understanding of fungal diversity in rice ecosystems.