The effect of substrate on the growth of population density of Trichoderma harzianum (TrH 40)

Abstract

Trichoderma harzianum is an efficient biocontrol agent that is commercially produced to prevent the development of several pathogenic soil fungi. Successful implementation of the bioagent can be achieved by preparation of microbial biomass with high population density and with high levels of viability and vigour. The most critical aspect o f introducing ormulations of biocontrol agent to the agriculture is the lack of knowledge of proper mass production and deliveiy systems. Therefore this study aimed at identifying the most suitable locally available culture medium for the production of Trichoderma harzianum (TrH 40) and the determination of effects of different substrates on shelf life of the same. The moisture level of four substrates, Rice husk, Kurakkan, white rice and red rice was adjusted to (30-60%) and inoculated with spore suspension prepared from 7-day-old culture of T. harzianum (TrH 40). All the sterilized and inoculated substrates were incubated in Erlenmeyer flasks at 28°C for 14 days. Population density of T. harzianum in stored substrates was estimated by counting the colony forming units (cfu/g). Suitable range of dilution to obtain the ideal number o f colonies of T.harzianum was determined. Population counts were taken at 27th, 35*, 47* and 54* days after inoculation. Results indicated that serial dilution up to 10'10 were more suitable for culturing in potato dextrose agar (PDA) plates and starting from 10"6 it gave the most suitable number of colonies to be count. All the substrates in the dilution range selected showed an effective propagation of T.harzianum (TrH 40). At the 27* day, the population count was maximum in the Kurakkan (2.2* 1010 cfu/g) medium. Results of the statistical analysis (Two way ANOVA) revealed that all the substrates equally support growth (p=0.492>0.05) of the organism. Rice husk is the best substrate, showing an increase in population during the storage period. Maximum population density was recorded in the white rice after 35 days. But viability declined within a short period of time.