Control Effect and Mechanism of Trichoderma asperellum TM11 against Blueberry Root Rot

Abstract

Fusarium oxysporum is the primary pathogen of blueberry root rot; furthermore, we found that Fusarium commune can also cause root rot in blueberries. Trichoderma spp. is widely used to control plant diseases. We isolated Trichoderma asperellum (TM11) from blueberry rhizosphere soil to explore its control effect and mechanism on F. oxysporum and F. commune. We found that the inhibitory effects of TM11 volatiles and broth metabolites on F. oxysporum were significant, but only F. commune volatile metabolites had a significant inhibitory effect on its growth. Twelve known antimicrobial metabolites were detected from the methanol extract of TM11 fermentation broth by HPLC-MS. TM11 lysed and coiled around the hyphae of F. oxysporum and F. commune. The pot experiment showed that TM11 had significant control effects against F. oxysporum and F. commune, and inoculation of TM11 prior to that of F. oxysporum and F. commune was more effective. The TM11, TM11 and F. oxysporum, or F. commune and distilled water treatments had different effects on the activities of superoxide dismutase, peroxidase and catalase, and the enzyme activity levels exhibited the following order: TM11 > TM11 and F. oxysporum or F. commune > distilled water. The results showed that TM11 provided effective control of blueberry root rot.

Keywords: Trichoderma asperellum; biocontrol mechanisms; blueberry root rot; pot tests.

Fig. 1.

Inhibitory activity of strain TM11 against Fusarium commune and Fusarium oxysporum. CK is F. commune and F. oxysporum alone; on the left side of each plate is the TM11 colony, and on the right side is the colony of F. commune or F. oxysporum.

Fig. 2.

Morphological characteristics of strain TM11. A–B) colony of TM11 surface and base, C) conidiophores, D) conidia (scale 20 microns).

Fig. 3.

Phylogenetic trees based on ITS (A) and SSU (B) sequences using the neighbor-joining method. The outgroup was Schizophyllum commune and Nectria berolinensis; numerical values above the branches are bootstrap percentiles from 1,000 replicates. Parsimony bootstrap values of more than 50% are shown at the nodes.

Fig. 4.

Inhibition of Fusarium oxysporum and Fusarium commune hyphal growth by Trichoderma asperellum strain TM11 under a microscope. A) Strain TM11 causes lysis of F. oxysporum lysis of the hyphae (as shown by arrow), B) strain TM11 causes F. oxysporum lysis of the hyphae, and the cytoplasm has leaked out of that hyphal (as shown by arrow), C) strain TM11 to coil around the hyphae of F. commune (as shown by arrow), D) strain TM11 causes F. commune lysis of the hyphae, and the cytoplasm has leaked out of that hyphal (as shown by arrow).

Fig. 5.

Inhibitory effects of volatile metabolites and fermentation metabolites of Trichoderma asperellum strain TM11 on the growth of Fusarium commune and Fusarum oxysporum. CK1 and CK2 represent the growth of F. commune and F. oxysporum on PDA; volatile metabolites mean volatile organic compounds (VOCs) and fermentation metabolites mean secondary metabolites, including alkaloids, ketones, esters, phenols and organic acids, such as erucamide, dibutyl phthalate and benzophenone.

Fig. 6.

Effect of blueberry seedling growth inoculated with Fusarium oxysporum or Fusarium commune. A) Control group: inoculated with F. commune alone, B) treatment 1: F. commune inoculated first, and TM11 inoculated 48 hours later, C) treatment 2: TM11 inoculated first, then F. commune inoculated 48 hours later, D) control group: inoculated with F. oxysporum alone, E) treatment 1: F. oxysporum inoculated first, and TM11 inoculated 48 hours later, F) treatment 2: TM11 inoculated first, then F. oxysporum inoculated 48 hours later.