The Beneficial Fungus <i>Trichoderma afroharzianum</i> T22 Increases Lettuce Yield but Does Not Reduce Verticillium Wilt Disease Under Field Conditions

Trichoderma spp. can suppress plant diseases and increase crop growth. However, few studies have tested their effects on lettuce grown in pathogen infested soil at the field scale. This study evaluated effects of the commercial strain T. afroharzianum T22 on lettuce in a field infested with the soilborne pathogen Verticillium dahliae. Field experiments were conducted over two consecutive seasons by applying Trichoderma afroharzianum T22 to soil as the active ingredient of Trianum-P. At harvest, disease severity was rated, lettuce head weight was measured, and rhizosphere soil was collected. The amount of T. afroharzianum T22 and V. dahliae in sampled soil was measured using previously developed qPCR assays. Verticillium wilt disease severity and the abundance of V. dahliae was not significantly different between control and T. afroharzianum T22 treated plots. Trichoderma afroharzianum T22 application significantly increased lettuce yield in both seasons and T. afroharzianum T22 was detected only in soil of treated plots. Outcomes of this research demonstrate T. afroharzianum T22 can significantly increase lettuce yield in pathogen infested soil and will provide lettuce growers additional options for improving crop productivity.