Involvement of metabolic components, volatile compounds, PR proteins, and mechanical strengthening in multilayer protection of cucumber plants against Rhizoctonia solani activated by Trichoderma atroviride TRS25

Justyna Nawrocka,U Małolepsza,M Szczech,K Szymczak

doi:10.1007/s00709-017-1157-1

Justyna Nawrocka, U Małolepsza + Show 2 more

Open Access

https://doi.org/10.1007/s00709-017-1157-1

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Abstract

In the present study, the spread of Rhizoctonia solani-induced disease was limited when cucumber plants were pretreated with Trichoderma atroviride TRS25. The systemic disease suppression was related to TRS25-induced resistance (TISR) induction with simultaneous plant growth promotion. Protection of cucumber was related to enhanced activity of defense enzymes, e.g., guaiacol peroxidase (GPX), syringaldazine peroxidase (SPX), phenylalanine ammonia lyase (PAL), and polyphenol oxidase (PPO) as well as phenolic (PC) concentration increases in the conditions of hydrogen peroxide (H2O2) accumulation, resulting in thiobarbituric acid reactive substance (TBARS) decrease. Moreover, the obtained results indicated that TISR might depend on accumulation of salicylic acid derivatives, that is methyl salicylate (MeSA), ethylhexyl salicylate (EHS), salicylic acid glucosylated conjugates (SAGC), and β-cyclocitral as well as volatile organic compounds (VOC) such as Z-3-hexanal, Z-3-hexenol, and E-2-hexenal. The results point to important, not previously documented, roles of these VOC in TISR signaling with up-regulation of PR1 and PR5 gene characteristic of systemic acquired resistance (SAR) and of PR4 gene, marker of induced systemic resistance (ISR). The study established that TRS25 enhanced deposition of callose and lignin in specialized plant cells, which protected vascular system in cucumber shoots and roots as well as assimilation cells and dermal tissues in shoots and leaves. These compounds protected cucumber organs against R. solani influence and made them more flexible and resilient, which contributed to better nutrition and hydration of plants. The growth promotion coupled with systemic mobilization of biochemical and mechanical strengthening might be involved in multilayer protection of cucumber against R. solani activated by TRS25.

Highlights

Rhizoctonia solani is one of the most destructive soil-borne necrotrophs
The growth promotion coupled with systemic mobilization of biochemical and mechanical strengthening might be involved in multilayer protection of cucumber against R. solani activated by TRS25
In TRS25-induced TISR, systemic enhancement of defense enzymes including guaiacol peroxidase (GPX), syringaldazine peroxidase (SPX), phenylalanine ammonia lyase (PAL), and polyphenol oxidase (PPO) accompanied by accumulation of H2O2 and PC as well as decrease in lipid peroxidation was detected

Summary

Introduction

Rhizoctonia solani is one of the most destructive soil-borne necrotrophs. The pathogen induces damping-off, blight, rot of roots, and shoots in a variety of crop plants including cucumber (Singh et al 2002; Bartz et al 2010; Saberi et al 2013; Yousef et al 2013). Some strains act directly against pathogens via mycoparasitism, competition, and antibiosis (Elad 2000; Melo and Faull 2000; Vinale et al 2008; Monfil and Casas-Flores 2014; Vos et al 2015); others promote plant growth (Harman et al 2004; Aly and Manal 2009; Christopher et al 2010; Yadav et al 2011) or induce natural plant protection at the site of infection as well as at distance to the pathogen resulting in alteration of the plant systemic resistance (Harman et al 2004; Singh et al 2010; Hermosa et al 2012; Yousef et al 2013; López-Bucio et al 2015; Vos et al 2015; Zhang et al 2016). Simultaneous cucumber growth promotion and up-regulation of systemic resistance against pathogens are observed less frequently and still need elucidation (Shoresh et al 2005; Harman et al 2012; Mathys et al 2012)

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