Cross Interaction Between Ilyonectria mors-panacis Isolates Infecting Korean Ginseng and Ginseng Saponins in Correlation with Their Pathogenicity

Abstract

Ilyonectria mors-panacis belongs to I. radicicola species complex and causes root rot and replant failure of ginseng in Asia and North America. The aims of this work were to identify I. mors-panacis that infect Korean ginseng using molecular approaches and to investigate whether their aggressiveness depends on their ability to metabolize ginseng saponins (ginsenosides) by their β-glucosidases, in comparison with other identified Ilyonectria species. Fourteen isolates were collected from culture collections or directly isolated from infected roots and mainly identified based on histone H3 (HIS H3) sequence. Among them, six isolates were identified as I. mors-panacis while others were identified as I. robusta and I. leucospermi. The pathogenicity tests confirmed that the isolates of I. mors-panacis were significantly more aggressive than I. robusta and I. leucospermi. The major ginsenosides in I. mors-panacis-infected roots were significantly reduced while significantly increased in those infected with other species. In vitro, the isolates were tested for their sensitivity and ability to metabolize the total major ginsenosides (Total MaG), protopanaxadiol-type major ginsenosides (PPD-type MaG), and protopanaxatriol-type major ginsenosides (PPT-type MaG). Unexpectedly, the growth rate and metabolic ability of I. mors-panacis isolates were significantly low on the three different ginsenoside fractions while those of I. robusta and I. leucospermi were significantly reduced on PPT-type MaG and Total MaG fractions and not affected on PPD-type MaG fraction. Our results indicate that major ginsenosides, especially PPT-type, have an antifungal effect and may intervene in ginseng defense during Ilyonectria species invasion, in particular the weak species. Also, the pathogenicity of I. mors-panacis may rely on its ability to reduce saponin content; however, whether this reduction is caused by detoxification or another method remains unclear.