Conidial Biomass and Desiccation Tolerance of Trichoderma harzianum Produced at Different Medium Water Potentials

Fungal biomass to be used for biological control of plant pathogens must be economical to produce, able to withstand desiccation, and stable under storage conditions. Polyethylene glycol (PEG) 200 was added to modified Richard's medium (RM8) to create different medium water potentials for producing Trichoderma harzianum. Water potentials of RM8 and RM8 with 6% (v/v) PEG 200 were -0.82 and -1.88 MPa, respectively. As medium water potentials were lowered with increasing concentrations of PEG 200 in RM8, the biomass dry weights decreased. However, conidial density and colony forming units (cfu) in the dry biomass were significantly improved to a maximum at -1.88 MPa. The total cfu number (biomass dry weight x cfu/g) in the dry biomass produced in RM8 at -1.88 MPa was increased on the average about 14-fold over that produced in RM8 alone. Although the cultivation temperatures did not affect the yield of the biomass, raising the cultivation temperature to 30 degrees C and lowering the medium water potential to -1.88 MPa at 24 h of fungal growth enhanced conidial formation and cfu numbers after drying. Under these growth conditions, conidiophores were formed within 12 h after PEG 200 was added; intensive conidiation occurred within 48 h and reached the maximum level in 84 h of incubation. Trehalose levels have been correlated with desiccation tolerance of T. harzianum. The concentration of trehalose in the dried conidial biomass produced in this manner was higher than that produced in RM8 alone, and the germination percentage of the dried conidia was 65%. (C) 1991 Academic Press, Inc.