Phyllosticta rizhaoensis sp. nov. causing leaf blight of Ophiopogon japonicus in China

Abstract

Ophiopogon japonicus (Asparagaceae) is a perennial grass species which can be cultivated as an ornamental and medicinal plant. From April 2021 to September 2022, a serious leaf blight disease of O. japonicus was discovered in Rizhao City, Shandong Province, China. The initial disease symptoms were small yellow spots, finally developing as tip blight, often associated with many small, black, semi-immersed pycnidial conidiomata formed in lesions. To obtain isolates of the causal agent for this disease, samples were randomly collected from O. japonicus diseased leaves in Rizhao City. In total 97 Phyllosticta isolates were obtained from samples, and studied using morphological features and multilocus phylogenetic analyses of a combined dataset using the internal transcribed spacers (ITS), the 28S large subunit of ribosomal RNA (LSU), and partial translation elongation factor 1-alpha (tef), actin (act) and glyceraldehyde-3-phosphate dehydrogenase (gapdh) loci. Phylogenetically, these Phyllosticta isolates formed a clade in the P. concentrica species complex, and clustered with P. pilospora and P. spinarum. Morphologically, isolates in this clade differed from P. pilospora and P. spinarum by the size of conidiogenous cells and conidia, and the absence of an apical conidial appendage. As a result, these isolates were described as a novel species Phyllosticta rizhaoensis. Pathogenicity was confirmed using Koch's postulates, which showed that P. rizhaoensis could induce leaf blight symptoms on O. japonicus in China.