Fungal diversity in agricultural soil under different farming management systems, with special reference to biocontrol strains of Trichoderma spp.

Fungal communities and their dynamics were investigated in relation to season, soil type and farming management practice. The research was done using soils from high- (H) and low-yield areas (L) of a field site cultivated with winter wheat under two different farming management systems (precision fanning, P; conventional farming, C) over the vegetation period. Fungal diversity was analysed by cultivation-independent methods [direct extraction of DNA from soil followed by PCR amplification of a subunit of the 18S rDNA and fingerprinting (DGGE)] as well as cultivation-dependent techniques (isolation of pure cultures). The comparisons of the PCR amplicons by DGGE patterns showed no differences between the different sampling sites and no influence of the farming management systems. Only small differences were observed over the vegetation period. For cultivation purposes active hyphae were isolated using a soil-washing technique. The resulting isolates were subcultured and grouped by their morphology and genotype. In contrast to the cultivation independent approaches, clear site-specific and seasonal effects on the fungal community structure could be observed. However, minor effects of the different farming management techniques applied were visible for active populations. These results clearly indicate that the potential fungal community (including spores), investigated by the cultivation-independent approach, is almost entirely uninfluenced by the investigated factors, whereas active populations show a clear response to environmental changes. The most abundant group consisting of Trichoderma species was investigated in more detail using strain-specific genotype based fingerprinting techniques as well as a screening for potential biocontrol activity against the wheat pathogen Fusarium graminearum. The genotypic distribution as well as the potential biocontrol activity revealed clear site-specific patterns.