Promotion of symbiosis between plants and arbuscular mycorrhizal fungi using crude drug extract derived from plants belonging to the Gentianaceae family

Abstract

Abstract : Arbuscular mycorrhizal (AM) fungi can establish a mutual symbiotic relationship with approximately 70% of terrestrial plants in their roots and supply them with phosphate. Thus, inoculation with AM fungi leads plants to use the phosphate efficiently and improve growth even under phosphate-starvation conditions. We previously demonstrated that secoiridoid glycosides derived from plants belonging to family Gentianaceae can promote hyphal branching and colonization of AM fungi. The present study investigated whether gentian crude drug extract could replace chemical secoiridoid glycoside and be developed as a new agricultural resource at a low cost. The amount of secoiridoid glycoside in a hot water extract of the gentian crude drug (Ryutan) was measured by high-performance liquid chromatography, which was used for the experiments. Bioassay using AM fungus revealed that the crude drug extract promoted hyphal branching equivalent to that promoted by chemical secoiridoid glycoside. Furthermore, treatment with crude drug extract substantially enhanced the colonization rate of AM fungus in chives and tomatoes. Expression analysis of marker genes for symbiosis in tomatoes revealed no significant changes after treatment with crude drug extract. Considering that crude drug extract had no effect on plant growth, our results demonstrate that gentian crude drug extract can be used as secoiridoid glycoside derived from plants belonging to the Gentianaceae family.