Effectiveness of Trichoderma application through drip-irrigation to reduce Sclerotinia disease incidence and improve the growth performance of greenhouse lettuce

A greenhouse experiment was carried out during the winter growing season in 2015 in Ladispoli (central Italy) to assess the influence of Trichoderma atroviride strain AT10 on shoot fresh biomass and resistance against the soilborne pathogen Sclerotinia spp. of lettuce crop (Lactuca sativa L. 'Canasta') grown in a naturally infested soil. T. atroviride strain AT10 was applied five times (1, 11, 24, 34 and 49 days after transplanting) by drip irrigation at a rate of 1 kg ha(-1) for each application. Lettuce drop caused by Sclerotinia spp. appeared at 49 days after transplanting where untreated plants (control) showed a higher mortality than plant treated with T. atroviride (4.0 vs. 0.9%). The disease incidence increased significantly at 56 days after transplanting with higher value in control plots than in plots treated with T. atroviride AT10 (4.1 vs. 2.4%). At the end of the trial (61 days after transplanting) the disease incidence reached 8.5% in control plot and 3.3% in treated plots. The efficacy of Trichoderma treatments in reducing the disease incidence in comparison with control treatment was calculated with the Abbott's formula and varied from 42.1 to 77.2%. The antagonistic activity of T. atroviride strain AT10 against Sclerotinia was demonstrated through in vitro tests. At harvest, lettuce plants inoculated with T. atroviride strain AT10 had a 13% higher shoot fresh weight than untreated plants indicating a phytostimulation action of the endophytic fungus.