Formation of sclerotia by Morchella esculenta: relationship between media composition and turgor potential in the mycelium

An improved experimental system was devised to study the influence of medium composition and water potentials on the formation of sclerotia by Morchella esculenta. A Petri dish was divided into two by a plastic barrier. One side of this split plate contained nutrient-poor medium (Noble agar), while the other side contained nutrient-rich medium (PDA). Inoculum placed on the poor side grew towards the rich side, ultimately producing sclerotia mainly on the poor side. The effect of salts, sugars and PEG, and the resultant water potentials in the poor medium was studied. Salts inhibited the production of sclerotia, while sugars, especially hexoses and hexitols, enhanced it. When sugars were added, the formation of sclerotia increased until the water potential dropped to −2·1 MPa. Below this value, the rate of sclerotial formation decreased. A positive correlation was found between the turgor potential generated in the mycelium and the quantity of sclerotia produced. It was concluded that two factors are crucial to sclerotial formation on a split plate: optimal water potential of the medium, causing a turgor potential in the hyphase conductive to morphogenesis, and the type of sugar added to the poor medium.