Piriformospora indica is an axenically cultivable root endophytic fungus which exerts plant growth promoting effects on its host plants. To enable commercial production of its spores, the medium composition and culture conditions have been optimized in a 14 L bioreactor such that they result in maximum biomass during growth phase and in maximum spore yield during subsequent sporulation phase. Maximum spore yields were obtained with modified Kaefer medium using a glucose deprivation strategy. An enhancement of 100% in overall biomass productivity (0.18 g L(-1) h(-1)) and reduction of about 70% in the time (60 h) required to achieve the maximum spore yield (9.25 x 10(7) spores/mL) was achieved in comparison to the original Kaefer medium. The high spore yield obtained in the present study seems to be economical for commercial production of P. indica. (C) 2010 Elsevier Ltd. All rights reserved.