Effect of metabolites from different Trichoderma strains on the growth of Rosellinia necatrix, the causal agent of avocado white root rot

Abstract

Seven different strains of Trichoderma isolated from avocado roots showed antagonism to Rosellinia necatrix, which is the causal agent of white root rot. We studied these Trichoderma strains on the basis of the secondary metabolites produced in liquid culture. Five different compounds, namely, 6PP (6-pentyl-α-pyrone), Harzianolide (4-hexa-2,4-dienyl-3-(2-hydroxy-propyl)-5H-furan-2-one), T39butenolide (4-hexa-2,4-dienyl-3-(2-oxo-propyl)-5H-furan-2-one), Dehydroharzianolide (4-hexa-2,4-dienyl-3-propenyl-5H-furan-2-one) and Cerinolactone [(3-hydroxy-5-(6-isopropyl-3-methylene-3, 4, 4a, 5, 6, 7, 8, 8a-octahydronaphthalen-2-yl) dihydrofuran-2-one); a recently discovered novel metabolite], were obtained. In vitro studies of the effects of these compounds on different R. necatrix strains isolated from avocado roots and with different virulence demonstrated that 6PP had the strongest effect even at a low concentration. Although unstable, Cerinolactone and T39butenolide also had large effects on R. necatrix, mainly at a concentration of 200 μg. Harzianolide and Dehydroharzianolide exhibited the lowest effects on the pathogen. In vivo studies of Trichoderma metabolites on Lupinus luteus plants demonstrated the delay of white root rot epidemic through preventive application of 6PP or Harzianolide to seeds or plantlets by immersion in solutions of these metabolites at 1 mg l⁻¹ (minimum effective dosage). In contrast, Cerinolactone only was effective at 10 mg l⁻¹ when applied by plantlet immersion. Thus, this study reports the role that these metabolites could play for controlling avocado white root rot caused by R. necatrix.