Identification and characterization of <i>Alternaria tenuissima</i> and <i>A. alternata</i> causing leaf spot of <i>Potentilla anserina</i> L. in China

Potentilla anserina L. is widely recognized for its extensive applications in traditional medicine and as a food source, harboring abundant bioactive compounds that confer significant medicinal and economic value. However, a severe disease consisting of leaf spots has adversely impacted P. anserina yield and quality in Heilongjiang Province, China. This study aims to identify the causal agent(s) of the disease, characterize the pathogen(s), and screen for effective control means. A total of 128 isolates were obtained from spotted leaves of P. anserina, with Alternaria tenuissima accounting for 68.7% and A. alternata for 32.3% of the isolates. These species were identified according to morpho-molecular characteristics and phylogenetic analyses. According to pathogenicity tests, A. alternata and A. tenuissima are both highly pathogenicity to P. anserina. In addition, all isolates were highly pathogenic to Astragalus laxmannii, Glycyrrhiza uralensis, and Trifolium pratense, moderately pathogenic to Artemisia argyi，and Beta vulgaris, and did not infect Mentha canadensis, Glycine max, Arachis hypogaea or Capsicum annuum. The isolates of A. alternata and A. tenuissima exhibited high sensitivity to benzoxystrobin and the biological control agent Paenibacillus polymyxa, with EC50 and IC50 values ranging from 0.09 to 0.57 µg/ml and 0.07 to 0.12 mg/ml, respectively. The efficacies varied between 96.1% and 97.5% at 480 μg/ml and between 95.1% and 97.1% at 240 mg/ml, respectively. According to this study, the pathogens responsible for P. anserina leaf spot in Heilongjiang, China, are A. tenuissima and A. alternata. Both showed high pathogenicity, but were effectively controlled by benzoxystrobin and Paenibacillus polymyxa, suggesting chemical treatments, intercropping and biocontrol as management strategies.