Seed-Associated Fungal Diversity and the Molecular Identification of Fusarium with Potential Threat to Ginseng (Panax ginseng) in China

Abstract

The utility of traditional methods for detecting seed-borne fungi is limited by the fact some fungi are unculturable or difficult to isolate. The seed-borne pathogens affecting Panax ginseng cultivation have not been fully characterized. Seed-borne fungi can be identified based on the high-throughput sequencing of internal transcribed spacer (ITS) amplicons. A hierarchical clustering tree diagram analysis based on operational taxonomic units revealed a relationship between the seed-borne fungi and the region from which the seeds were collected. This study analyzed the fungal diversity on 30 ginseng seed samples from the main ginseng-producing areas of China. The 50 most abundant genera were identified including those responsible for ginseng diseases, Fusarium, Alternaria, Nectria, Coniothyrium, Verticillium, Phoma, and Rhizoctonia. Fusarium species, which are the primary causes of root rot, were detected in all seed samples. The results of a phylogenetic analysis indicated that the seed-borne fungal species originating from the same region were closely related. Fungi on ginseng seeds from eight different regions were divided into eight clades, suggesting they were correlated with the local storage medium. A total of 518 Fusarium isolates were obtained and 10 species identified, all of which can be detrimental to ginseng production. Pathogenicity tests proved that seed-borne Fusarium species can infect ginseng seedlings and 2-year-old ginseng root, with potentially adverse effects on ginseng yield and quality.