Development of trichoderma-stock culture production for farmers

Microbial contamination is a major problem involved in the stock culture production of Trichoderma harzianum by using autoclaved sorghum seeds as a substrate. Moreover, these stock culture could not be kept longer than 2 wk at room temperature. The objectives of this study included the development of appropriate culturing substrate for the production of Trichoderma-stock culture which could be kept longer at room temperature without loosing the quality and disease control efficacy. For culturing substrate preparation, the sieved fertile soil (Din-khui-pai) and washed river sand were mixed at the ratio 90:10 by weight, them the mix was blended with 1-2 hr-soaked broken rice at 10 percent by weight. Moisture content of the mixture was adjusted at 13-15 percent before autoclaving at 15 lb/square inch, 121 deg C for 30 min. This substrate provided good mycelial growth and sporulation of T. harzianum isolate CB-Pin-01. Population quantification of 30 day-old-stock culture incubated at 25 deg C by dilution spread plate on Martin medium revealed over 10**(8) colony forming units (cfu)/g. Quality evaluation was conducted by inoculating 5 g of stock culture into 1 kg steamed soaked broken rice. Good mycelial growth and sporulation of T. harzianum observed on steamed soaked broken rice indicated the high quality of stock culture. For storage storage study, stock cultures using various rates of broken rice including 10, 20, 30, 40 and 50 percent by weight were preserved at 8-10, 22-25 and 25-32 deg C for 180 days. At 30 days after storing, all stock cultures provided over 10**(8) cfu/g with high quality of growth and sporulation. However, when storing periods were prolonged upto 90 and 180 days, only stock cultures preserved at 8-10 deg C retained their viability and quality. Determination of disease control efficacy of Trichoderma culturing on steamed broken rice produced from stock cultures (10 percent broken rice) stored at 8-10, 22-25 and 25-32 deg C for 30 days was performed by mixing fresh culture with ricebran and compost at 1:10:40 by weight before broadcasting each ready mix on the yard-long bean planting soil at 100 and 150 g/square m. All Trichoderma cultures could control the damping-off of yard-long bean caused by Sclerotium rolfsii. Their efficacies were comparable to the use of commercial Trichoderma biofungicide (Unigreen UN-1) at a rate 50 g/square m. In trichoderma treatments, the significantly higher percent surving plants and the lower sclerotial numbers as compared to the control were observed. When stock cultures stored for 90 and 180 days were used, only fresh inoculum produced from stock cultures preserved at 8-10 and 22-25 deg C retained effectiveness for controlling damping-off.