Cold-tolerant Trichoderma species for the managementof Fusarium wilt of tomato plants

Abstract

Cold-tolerant Trichoderma species capable of growing at 5 °C were isolated from rhizospheric soils of the western Himalayan region. Sequencing of the internal transcribed spacer region revealed that these isolates were taxonomically affiliated to Trichoderma gamsii, Trichoderma velutinum and Hypocrea lixii. The isolate showing maximum antagonism against Fusarium oxysporum f.sp. lycopersici (FOL), PETX-Behli-1 (T. gamsii), was studied for its chitinolytic ability. This isolate displayed maximum chitinolysis on chitinase detection agar, with the extracellular proteins in minimal synthetic broth (MSB) amended with colloidal chitin showing higher chitinase activities of 63.1- to 83.8-fold at 5–37 °C than those in MSB alone. Extracellular proteins of cell-free extracts of MSB amended with and without chitin contained polypeptides of 26–180 kDa. In the plate assays, the crude extract containing chitinases inhibited mycelial growth of the pathogenic fungus by 42 %. Seed bacterization and soil application of the chitin-supplemented talc-based formulation of PETX-Behli-1 challenge inoculated with FOL resulted in a significantly lower incidence (61.9 % reduction) of Fusarium wilt relative to the non-bacterized pathogen control in a greenhouse (18–20 °C). This lower incidence was associated with an increase in the plant vigor index, fruit number and fruit weight of 64.8, 205.4, and 210.8 %, respectively, relative to the pathogen control. In the native gel activity assays, PETX-Behli-1 following challenge inoculation expressed a higher intensity or an increased number of isoforms of chitinase, peroxidase and polyphenol oxidase. The results suggest that the cold-active PETX-Behli-1 may represent an important biocontrol agent to control Fusarium wilt of tomato plants grown in winter.