Effects of experimental conditions on mycorrhizal relationships between Pinus sylvestris and Lactarius deliciosus and unprecedented fruit-body formation of the Saffron milk cap under controlled soilless conditions

The mycorrhizal relationships between pines and two edible species of Lacta rius sect. Dapetes were investigated by optimizing the experimental conditi ons of mycelial growth and of mycorrhizal colonization of pine seedlings. I n vitro mycelial growth of Lactarius deliciosus and L. sanguifluus was impr oved on a buffered medium containing glucose, amino acids, and vitamins. Tw o methods of mycorrhization of pines with Lactarius deliciosus were tested. The mycorrhizal colonization was rapid and intense under non-aseptic condi tions with a low nutrient supply and without exogenous glucose. A positive influence of mycorrhizal colonization on Pinus sylvestris growth was subseq uently observed. Under axenic conditions and with a high nutrient supply, m ycorrhization was stimulated at 10 g/L of exogenous glucose, irrespective o f the phosphorus concentration. At high phosphorus level (1 mM) and 0.1, 1. 0, or 10.0 g/L glucose, growth of Pinus sylvestris was reduced by inoculati on. Stability and development of Pinus spp./Lactarius deliciosus symbioses were assayed in a climatic chamber using containers filled with a synthetic substrate. Over a 2-year culture period, the root systems of the pine seed lings were heavily colonized by Lactarius deliciosus. One year following in oculation, Lactarius deliciosus fruit-body primordia appeared associated wi th Pinus sylvestris seedlings. Six months later, two mature basidiomata wer e obtained. This is the first report of soilless fruit-body formation of th is edible mushroom.