Response of Lettuce Cultivars to Inoculation with Trichoderma spp.

Fungi of the Trichoderma genus are present in practically all types of soil and they have the ability to establish a beneficial relationship with plants. In addition to acting as direct biological control agents, they also act as plant growth promoters, by an indirect biological control mechanism. Because of these, many products containing Trichoderma strains are used to improve seed health, providing better development of roots and aerial parts of plants. In view of this fact, research work was carried out in a greenhouse with the aim of evaluating the effect of five Trichoderma strains, belonging to the species T. virens, T. asperellum, T. asperelloides, in addition to a strain unidentified at the species level T. koningiopsis, in three new crisp lettuce cultivars (BRS Lélia, BRS Leila, and BRS Mediterrânea). A conidial suspension of each of the strains was prepared (1.0 x 107 conidia mL-1) and applied at the time of sowing the lettuce in pots. The experiment was completely randomized in a factorial 5x3 design (Trichoderma spp. x cultivars). Control treatments consisted of pots containing plants without any of the fungi. All Trichoderma strains applied increased fresh mass and length of root, fresh mass of aerial part and lettuce height in comparison to the controls treated just with water. The cultivar BRS Leila showed an increase of 44% in fresh root mass, 45% in fresh mass of aerial part, with T. virens; 15% in plant height with T. koningiopsis, and 23.94% in root length, with Trichoderma sp. For ‘BRS Lélia’ the highest values ​​of fresh root mass, fresh mass of aerial part and root length were 30%, 36.71%, and 13.33% with T. asperellum. Trichoderma asperelloides provided 13.72% increase in height compared to the control. ‘BRS Mediterrânea’ showed increments of 75% of fresh root mass, 78.45% of fresh mass of aerial part, and 44.37% of height with T. virens. With T. asperelloides, 40.61% was observed in root length. The strain T. virens performed better in all the analyzed variables, except for root length.