Evolution of Trichoderma harzianum populations distribuited in peach orchards against Armillaria mellea

The aim of the work was to investigate the quantitative development of Trichoderma harzianum Rifai populations which were added in peach orchards to control Armillaria mellea (Vahl ex Fr.) Kummer. A two-year study (2000/01) was carried out in two peach orchards, located in the Cesena and Ravenna provinces, in which a T. harzianum-based commercial product was distributed in different doses in the planting holes. Soil samples were collected from different zones (rhizosphere of peach trees and between rows) of the two orchards, and the density of Trichoderma populations were quantified by serial dilution method in association with the use of a selective medium (Trichoderma-selective medium + propamocarb). The population density of Trichoderma was significantly higher, on average, in the rhizosphere of peach plants (2657 c.f.u./g) than between rows (uninoculated soil) (632 c.f.u./g), showing the successful settling down of the artificial inoculum. In the peach orchard located in Ravenna, this effect extended over at least 15 months after inoculum distribution.