DEVELOPMENT OF MEDIA AND AUTOMATED LIQUID FERMENTATION METHODS TO PRODUCE DESICCATION-TOLERANT PROPAGULES OF TRICHODERMA-HARZIANUM

A suitable medium was developed from modified Richard's medium plus V8 juice (RM8) to produce high levels of desiccation-tolerant conidia of Trichoderma harzianum strain 1295-22. The addition of 9% (v/v) glycer ol to RMS improved both biomass production and desiccation tolerance o f the conidia of T. harzianum. This medium was then used in a laborato ry scale fermenter (1.5 liter) to determine optimal operating conditio ns. The optimal temperature for conidial production and desiccation to lerance improvement in the fermenter was 32 degrees C when dissolved o xygen was maintained at 50% saturation of air, and the stirring rate w as 1000 revolutions per minute. The initial water potential of the med ium (with 9% glycerol) was -3.7 MPa, the pH was 6, and neither was con trolled during fermentation. Changes in medium pH and dissolved oxygen were associated with the stages of morphological development and coni diation. The pH of the medium decreased concurrently with germ-tube el ongation and mycelium development and then increased to 6.0-6.2 at phi alide formation. Intensive conidiation occurred at pH 6.3-6.5 and reac hed its maximal level at 6.9-7.1. Changes in pH values could be used a s indicators to monitor the morphological development and conidiation of T. harzianum during fermentation. The use of a 48-h-old culture ino culum, rather than conidial inoculum, to start fermentation reduced th e time required to complete the shift from vegetative growth to phiali de formation. Intensive conidiation occurred immediately after the add ition of culture inoculum and reached maximum levels within 68 h of fe rmentation. Dry weight of biomass increased with the duration of ferme ntation and was greatest at 96 h. However, no improvements in conidia/ gram and CFU/gram were achieved after 72 h of fermentation. The desicc ation tolerance of conidia harvested at 72 or 96 h was significantly ( P = 0.05) greater than that of conidia harvested at 48 h of fermentati on. Results obtained from this study could be used for further scale-u p of the fermentation process. (C) 1996 Academic Press, Inc.