The Application of Trichoderma Strains or Metabolites Alters the Olive Leaf Metabolome and the Expression of Defense-Related Genes

Roberta Marra,Nadia Lombardi,Sergio Bolletti Censi,Francesco Vinale,Mariangela Coppola,Giada D’Errico,Andrea Sicari,Angela Pironti,Filomena Grasso,Rosa Rao,Sheridan L Woo

doi:10.3390/jof6040369

Abstract

Biocontrol fungal strains of the genus Trichoderma can antagonize numerous plant pathogens and promote plant growth using different mechanisms of action, including the production of secondary metabolites (SMs). In this work we analyzed the effects of repeated applications of selected Trichoderma strains or SMs on young olive trees on the stimulation of plant growth and on the development of olive leaf spot disease caused by Fusicladium oleagineum. In addition, metabolomic analyses and gene expression profiles of olive leaves were carried out by LC–MS Q-TOF and real-time RT-PCR, respectively. A total of 104 phenolic compounds were detected from olive leave extracts and 20 were putatively identified. Targeted and untargeted approaches revealed significant differences in both the number and type of phenolic compounds accumulated in olive leaves after Trichoderma applications, as compared to water-treated plants. Different secoiridoids were less abundant in treated plants than in controls, while the accumulation of flavonoids (including luteolin and apigenin derivatives) increased following the application of specific Trichoderma strain. The induction of defense-related genes, and of genes involved in the synthesis of the secoiridoid oleuropein, was also analyzed and revealed a significant variation of gene expression according to the strain or metabolite applied.

Highlights

Olive (Olea europaea L.) has played a fundamental role for the development of Mediterranean civilizations in the economic, social, and cultural areas [1,2]
Our results showed that strains TH1 and T22 and the metabolite 6PP determined a significant reduction of foliar symptoms associated to the olive peacock spot disease
The treatments determined an increase in plant biometric parameters, and a reduction in the number of leaves affected by peacock spot disease compared to controls

Summary

Introduction

Olive (Olea europaea L.) has played a fundamental role for the development of Mediterranean civilizations in the economic, social, and cultural areas [1,2] It is the second most important oil fruit crop in the world, after oil palm, cultivated over 8 million hectares of land, largely concentrated in the Mediterranean basin [3,4]. Olive leaves represent a valuable waste byproduct of olive cultivation and processing, rich of bioactive compounds [6,7] These include phenolic compounds, which have shown numerous positive effects on human health (i.e., antihypertensive, antiinflammatory, hypoglycemic, antimicrobial, and hypocholesterolemic) that were mainly related to an antioxidative action (see [7] for a review)

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Conclusion