Distribution and Molecular Phylogeny of Fusarium Species Associated with American Ginseng Root Rot in China.

American ginseng (Panax quiquefolium L) of the Araliaceae family is a medicinal and functional herbal originated in North America. In the 1980s, American ginseng was successfully introduced in China and is now grown mainly in Jilin province and Shandong province. Root rot of American ginseng is a major problem that causes reduction in yield and quality in the major ginseng production regions of China. Fusarium is an important and typical soil-borne genus, and several species exist in association with American ginseng root disease in all growing seasons and years. In the present study, 1 to 4-year-old American ginseng root samples were collected from 10 fields located in Jilin and 9 fields located in Shandong. A total of 506 isolates were obtained from Jilin and Shandong (199 and 307, respectively). Fusarium species were isolated most frequently (36% of the total isolates) from disease tissues and identified by morphological characteristics and sequencing of the translation elongation factor (EF1-α). Nine Fusarium species were identified as, F. oxysporum, F. solani, F. proliferatum, F. armeniacum, F. acuminatum, F. torulosum, F. equiseti, F. graminearum and F. commune. Species distribution and frequency of these fungi was influenced by root age, F. oxysporum were recovered mostly from 1 and 2-year-old roots (45% and 71%, respectively) while F. solani were recovered more often from 3 and 4-year-old roots (52% and 62%, respectively). F. oxysporum and F. solani were the two most frequent and widespread species. Conversely, several other species were only found in 1-year-old roots (F. armeniacum and F.equiseti), 3-year-old roots (F. graminearum), and 4-year-old roots (F. proliferatum, F. commune and F. torulosum). Besides, members of this phylogenetic species have a restrictive geographic distribution, either. Five species (F. oxysporum, F. solani, F. acuminatum, F. torulosum, and F. commune) and 6 species (F. oxysporum, F. solani, F. proliferatum, F. armeniacum, F. equiseti and F. graminearum) were recovered from Jilin and Shandong, respectively. This typification is consistent with the wide distribution of F. oxysporum and F. solani in root ages and geographic regions. Phylogenetic analysis of isolates in F. oxysporum and F. solani based on the combined sequences of internal transcribed spacer（ITS）and 2 protein coding genes (EF-1αandβ-tubulin) showed F. oxysporum populations from Jilin and Shandong clustered together in one group while 2 distinct groups were found in F. solani populations. Each groups corresponded to a specific geographical region Jilin or Shandong. Results from this study suggest that Fusarium species distribution in American ginseng was influenced by root age and the distribution of F. solani was correlated with geographical region.