Trichoderma spirale T76-1 displays biocontrol activity against leaf spot on lettuce (Lactuca sativa L.) caused by Corynespora cassiicola or Curvularia aeria

Lettuce (Lactuca sativa) is an edible leafy vegetable used in diverse recipes. The disease known as leaf spot leads to plant death and is caused Corynespora cassiicola or Curvularia aeria. In this study, 5 selected isolates of Trichoderma spp. were assessed for their antifungal activities against C. cassiicola and C. aeria. Trichoderma spirale T76-1 was superior in inhibiting the mycelial growth of C. cassiicola and C. aeria by 84.68% and 93.03%, respectively, in dual culture assays. In a volatile antifungal bioassay T. spirale T76-1 suppressed the growths of C. cassiicola and C. aeria by 41.29% and 42.35%, respectively. GC/MS profiling revealed the presence of antifungal compounds, including alcohol and pyran. Poisoned food technique showed that the cell-free culture filtrate of T. spirale T76-1 inhibited C. cassiicola and C. aeria by 48.47% and 51.67%, respectively. The enzyme activities of beta-1,3-glucanase and chitinase in the cell-free culture filtrate were 10.13 and 0.93 U mL(-1), respectively. Scanning electron microscopy of mycelia incubated with cell-free culture filtrate of T. spirale T76-1 showed abnormal shapes in both pathogens. Leaf spraying with a spore suspension of T. spirale T76-1 suppressed disease incidence by up to 58-62% compared to control (96-98% penetration, inoculation with pathogen alone). These findings reveal that competition, volatile antifungals, and enzyme activities are mechanisms involved in the biocontrol of leaf spot in lettuce by T. spirale T76-1.