Biocontrol ability of Trichoderma harzianum strain T22 against Fusarium wilt disease on water-stressed lettuce plants

The control ability of Trichoderma harzianum strain T22 against Fusarium wilt of lettuce caused by Fusarium oxysporum f.sp. lactucae strain 365.07 was studied through mesocosm assays under extreme soil water content available for plants (-0.5 and -0.03 MPa).T22 was applied to nursery substrate at seeding, and to mesocosm soil at transplant of seedlings artficially infected by the pathogen. T22 decreased disease severity in comparison to infected controls by 57 and 78% in dry and wet conditions, respectively. Plant biomass was increased by T22 under both moisture levels. T22 colony growth, spore germination and antagonism to the pathogen were investigated under different water potential ( -0.03, -0.1, -0.5, -1.0, -2.0, -7.0 and -14.0 MPa) on minimal agar medium. All these parameters were influenced by water potential. However, they were similar at the same MPa values tested in the mesocosm assays.Our results provide evidence that T. harzianum strain T22 could be effective to control wilt disease caused by F. oxysporum f.sp. lactucae strain 365.07 under extreme soil moisture regimes already present in Italy, and susceptible to become more frequent in the near future.