All the results during incubation, the brown pigmentation and the initiation of primordia suggest that the 2 parts of sawdust + 8 parts of rice straw formulation was the most suitable nutritional condition for the production of vigorous mycelia needed for advanced development of the reproductive phase. However, pure rice straw had the longest number of days in terms of primordial development, with a mean 30.6 d, while no primordia was observed in the 9 parts of sawdust + 1 part of rice straw formulation. Watanabe (2001, cited in Chen 2004) and Oei (1996) enumerated different factors that promote primordia initiation in L. edodes such as removal of CO2 or increasing the O2 supply, water spraying, temperature fluctuation, high humidity, and physical shocks such as agitation and disturbance.