Identification and host range test of leaf spot of Axonopus compressus

In 2022, an extensive outbreak of an unknown disease showing symptoms of brown, nearly round, or elongated spots on leaves was observed in the field of Axonopus compressus at the Songhuaba vegetable base in Kunming, Yunnan, China. To clarify the pathogenic species causing A. compressus leaf spot, the hypothetical pathogen was isolated and cultured, morphologically analyzed, multi-gene sequenced, and tested using Koch’s postulates. The results proved that the pathogen was confirmed as Bipolaris zeae. The host spectra of this pathogen were tested by spore suspension inocultaion. The results proved that it can infect twenty-one economically important crops and common weeds, including rice (Oryza sativa), maize (Zea mays), sorghum (Sorghum bicolor), wheat (Triticum aestivum), coix (Coix lacryma-jobi), palm grass (Setaria palmifolia), foxtail grass (Setaria viridis), wild oat (Avena fatua), ryegrass (Lolium perenne), and barnyard grass (Echinochloa crusgalli). Furthermore, the toxicity of seven chemicals against B. zeae was tested on plates, revealing that difenoconazole (0.381 mg∙L⁻¹) exhibited the highest efficacy in inhibiting its growth, followed by fluxapyroxad (0.988 mg∙L⁻¹), iprodione (1.864 mg∙L⁻¹), mancozeb (5.40 mg∙L⁻¹), thiophanate-methyl (930.57 mg∙L⁻¹), azoxystrobin (989.57 mg∙L⁻¹), and chlorothalonil (1 547.36 mg∙L⁻¹). The pathogens and host range of A. compressus leaf spot were clarified, and the fungicides with good antibacterial effect were selected. This study provides a theoretical basis for the diagnosis and prevention of this disease.