Identification and pathogenicity analysis of Alternaria alternata, the causal agent of leaf spot disease in Paris polyphylla var. yunnanensis

Paris polyphylla var. yunnanensis is an important perennial medicinal plant whose production is greatly limited by various diseases, including leaf spot disease recently reported in Yunnan, China. However, the causative agent of P. polyphylla leaf spot is still unknown. This study isolated and identified the causal agent of P. polyphylla leaf spot from leaf tissues of infected plants through morphological and molecular characterization. The isolated fungus was identified as Alternaria alternata based on its morphological characteristics and nucleotide sequences of the elongation factor 1-alpha (EF1α), nuclear ribosomal internal transcribed spacer (ITS), the 28S nuclear ribosomal large subunit rRNA gene (LSU), the 18S nuclear ribosomal small subunit rRNA gene (SSU), and the second largest subunit of nuclear DNA-directed RNA polymerase II (RPB2). The re-isolation of the isolate fulfilled Koch´s postulates, indicating that A. alternata was the causal agent of P. polyphylla leaf spot. The findings of this study will potentially pave the way for epidemiological forecasting and developing control strategies for this disease.