Monitoring of Trichoderma species in agricultural soil in response to application of biopreparations

•Application of T. atroviride/T. harzianum as biopreparations in lettuce cultivation.•Development of molecular markers for T. atroviride and T. harzianum identification.•Counting of Trichoderma spp. colonies in soil samples over time.•Identification of strains collected before and after biopreparations application.•Monitoring of Trichoderma population levels in soil over time with multiplex-PCR.

Strains of Trichoderma are used in crop plant production as plant growth promoters and biological control agents. In this study, strains of T. atroviride and T. harzianum, overgrown on organic material, were applied as biopreparations to the soil in open-field lettuce cultivation, and their population levels were monitored over time. A newly developed multiplex-PCR Trichoderma-identification technique was successfully used to confirm the increased abundance of T. atroviride and T. harzianum in the soil after biopreparations application, whereas these Trichoderma species were not detected in untreated soil. The results of multiplex-PCR were confirmed by standard plating and Trichoderma spp. colony counting of soil samples as well as by molecular identification of representative strains. Indigenous Trichoderma species were identified in field soil, however, their abundance was estimated to be relatively low 103 CFU, when compared to 105 CFU g−1 of dry soil, after biopreparations application, and these fungi persisted at this level even after two years.