Population dynamics of Trichoderma spp. in paddy fields soil

Fungi belonging to the genus Trichoderma are one of the most effective biocontrol agents of plant diseases. Because of importance of Trichoderma strains in agriculture and lack of information about their ecology and population dynamics in natural habitats in Iran, we studied seasonal changes of Trichoderma spp. populations and its relation to microbial competition and environmental factors (soil moisture, pH, EC, organic matter as well as precipitation and temperature). Three rice fields in North of Iran (Amol, Mazandaran province) were selected and sampling was performed monthly for one year at 15 cm soil depth. All microorganisms were isolated with dilution plate method, using general and selective media. Trichoderma, total fungi and bacterial populations in paddy soils ranged 1.1×101-11×103, 1.7×103-3.1×104 and 2.2×104-6.5×105 cfu/g soil, respectively. Highest Trichoderma population was recorded in late spring and during autumn for all fields, while, population was decreased in winter. According to the multiple linear regression analysis results, there was positive correlation between Trichoderma populations and soil moisture and electrical conductivity, and negative correlation with total fungal count (P=0.01). There was no significant correlation between Trichoderma populations and other factors.