Characterization of Novel Trichoderma asperellum Isolates to Select Effective Biocontrol Agents Against Tomato Fusarium Wilt

Abstract

The use of novel isolates of Trichoderma with efficient antagonistic capacity against Fusarium oxysporum f. sp. lycopersici (FOL) is a promising alternative strategy to pesticides for tomato wilt management. We evaluated the antagonistic activity of 30 isolates of T. asperellum against 4 different isolates of FOL. The production of extracellular cell wall degrading enzymes of the antagonistic isolates was also measured. The random amplified polymorphic DNA (RAPD) method was applied to assess the genetic variability among the T. asperellum isolates. All of the T. asperellum isolates significantly reduced the mycelial growth of FOL isolates but the amount of growth reduction varied significantly as well. There was a correlation between the antagonistic capacity of T. asperellum isolates towards FOL and their lytic enzyme production. Isolates showing high levels of chitinase and β-1,3-glucanase activities strongly inhibited the growth of FOL isolates. RAPD analysis showed a high level of genetic variation among T. asperellum isolates. The UPGMA dendrogram revealed that T. asperellum isolates could not be grouped by their anta- gonistic behavior or lytic enzymes production. Six isolates of T. asperellum were highly antagonistic towards FOL and potentially could be used in commercial agriculture to control tomato wilt. Our results are consistent with the conclusion that understanding the genetic variation within Trichoderma isolates and their biochemical capabilities are required for the selection of effective indigenous fungal strains for the use as biocontrol agents.

Keywords: Fusarium wilt; T. asperellum; cell wall degrading enzymes; molecular markers; mycoparasitism.

Fig. 1

Mycoparasitic action of T. asperellum isolate TS12 on the mycelium of F. oxysporum isolate FOL-4 showing overgrowth (A) and heavy sporulation (B).

Fig. 2

RAPD patterns of thirty T. asperellum isolates, generated by 10-mer random primer OPY-07.

Fig. 3

Dendogram illustrating the genetic relationship among thirty T. asperellum isolates varied in their antagonistic capabilities against Fusarium wilt pathogen. The scale portrays a similarity index based on Jaccard’s coefficient, and the dendrogram was developed using UPGMA clustering Procedure. The letters in parentheses indicate the antagonistic capabilities of T. asperallum isolates against Fusarium wilt pathogen: (H) high, (M) moderate and (L) low. Bootstrap values obtained from 1,000 replications are indicated above the tree branches. RAPD clusters are designated in roman numerals.