Phosphorus is a critical factor of the in vitro monoxenic culture method for a wide range of arbuscular mycorrhizal fungi culture collections

Establishing an effective way to propagate a wide range of arbuscular mycorrhizal (AM) fungi species is desirable for mycorrhizal research and agricultural applications. Although the success of mycorrhizal formation is required for spore production of AM fungi, the critical factors for its construction in the in vitro monoxenic culture protocol remain to be identified. In this study, we evaluated the growth of hairy roots from carrot, flax, and chicory, and investigated the effects of the phosphorus (P) concentration in the mother plate, as well as the levels of P, sucrose, and macronutrients in a cocultivation plate with a hairy root, amount of medium of the cocultivation plate, and location of spore inoculation, by utilizing the Bayesian information criterion model selection with greater than 800 units of data. We found that the flax hairy root was suitable for in vitro monoxenic culture, and that the concentration of P in the cocultivation plate was a critical factor for mycorrhizal formation. We showed that an extremely low concentration of P (3 μM) significantly improved mycorrhizal formation for AM fungi belonging to the Glomerales order, while a high concentration of P (30 μM) was suitable for Diversisporales fungi. Therefore, we anticipate that the refining the P concentration will contribute to future culture collections of a wide range of AM fungi.