The fruiting body formation of Flammulina velutipe is affected by some environmental factors:
Temperature: Temperature is one of the important factors in the control of mycelial growth and fruit body formation. The temperature extremes (maximum and minimum) are of great importance in determining the survival and distribution of a fungal species in nature . Generally, The optimum temperature for mycelial growth of Flammulina velutipe is between 22 and 26⁰C. The mycelium grows slowly, but does not die when exposed to a temperature of 3-4⁰C. On the other hand, at around 34⁰C growth ceases and at over 34⁰C the mycelium is killed instantly. The temperature necessary for primordium formation is between 10 and 20⁰C. Specifically, at a temperature of 15⁰C, it takes about 15 h for primordium formation, but at 5 or 10⁰C it takes about 48 h.
Moisture and humidity: Moisture of substrates and the humidity of the environmental air also affect the fungal growth. High humidity (90–95%) is favourable for pinning and fruiting of Flammulina velutipe but the moisture content of the substrate might be even more critical towards contamination. The optimal water content for wooden substrates is 35–60% and, for other substrates is 60–80%. The lower values reflect the oxygen demand of the fungi in the substratum, balanced against their requirement for water.
Oxygen supply: Flammulina velutipes is an aerobic species and, must be supplied with sufficient oxygen. Plunkett (1956) showed that under conditions of continuous exposure of carbon dioxide in the air: 1) pileus diameter decreased with increasing concentration of carbon dioxide(0.06-4.90% carbon dioxide); 2) stipe elongation was less sensitive to carbon dioxide than pileus expansion; and 3) stipe elongation and pileus expansion were both prevented by high concentration of carbon dioxide. According to Long (1966), the carbon dioxide inhibition of pileus growth can be limited to the expansion phase of pileus development and not to pileus formation and early growth.
Light intensity: Light is believed to stimulate the morphological changes that take place during basidiocarp formation of many basidiomycetes mushroom. It has been reported that F. velutipescan form basidiocarps in total darkness, although these basidiocarps lack mature pilei. It was shown that the diameter of the pileus increases in proportion to the light intensity (up to 100 lux) (Inatomi et al., 2001), and thus it is believed that the formation of the pileus of F. velutipesis stimulated by light.
Hydrogen ion concentration (pH) : pH has great effects on morphological development. The pH requirements for growth and fruiting differ as to their optimal values but not necessarily in the same direction from one species to another. Mycelial growth is less affected by pH, but basidiocarp development of several species occurs best at neutral or slightly acidic pH values around pH 6-7 . The pH change that occurs during growth (e.g., by the production of organic acids) may trigger the response from vegetative growth to fruiting.
Mechanical injury: The onset of basidiocarp development correlates with nutritional exhaustion of the growth substrates. Basidiocarp development for commercial mushroom production is thus often induced by covering compost colonized by vegetative mycelium with a layer of moist peat and chalk, which have only limited nutrient. Typically, mycelia of basidiomycetes are not uniformly competent to differentiate; and only young hyphae can be induced to initiate fruiting body development (Ross, 1982). Mechanical injury of established mycelium locally stimulates basidiocarp development, because wounding causes outgrowth of fresh hyphae. The molecular principles triggering differentiation are not known. Various substances with fruiting inducing activity in specific or several basidiomycetes have been described: cerebrosides , sucrose esters of fatty acids and other surfactants , cAMP and AMP , anthranilic acid and indole and other substances of yet unknown nature present in fungal extracts.