Reynoutria sachalinensis extract elicits SA-dependent defense responses in courgette genotypes against powdery mildew caused by Podosphaera xanthii

Theoni Margaritopoulou,Eleftheria Toufexi,Emilia Markellou,Leonidas Rempelos,Dimosthenis Kizis,Andreas Theocharis,Carlo Leifert,Christos Anagnostopoulos,Yerasimos Troyanos,George Balayiannis

doi:10.1038/s41598-020-60148-6

Abstract

Powdery mildew (PM) caused by Podosphaera xanthii is one of the most important courgette diseases with high yield losses and is currently controlled by fungicides and sulphur applications in conventional and organic production. Plant derived elicitors/inducers of resistance are natural compounds that induce resistance to pathogen attack and promote a faster and/or more robust activation of plant defense responses. Giant knotweed (Reynoutria sachalinensis, RS) extract is a known elicitor of plant defenses but its mode of action remains elusive. The aim of this study was to investigate the mechanisms of foliar RS applications and how these affect PM severity and crop performance when used alone or in combination with genetic resistance. RS foliar treatments significantly reduced conidial germination and PM severity on both an intermediate resistance (IR) and a susceptible (S) genotype. RS application triggered plant defense responses, which induced the formation of callose papillae, hydrogen peroxide accumulation and the Salicylic acid (SA) - dependent pathway. Increased SA production was detected along with increased p-coumaric and caffeic acid concentrations. These findings clearly indicate that RS elicits plant defenses notably as a consequence of SA pathway induction.

Highlights

Plants upon attack of pathogenic micro-organisms activate complex immune networks to prevent or minimize colonization of their internal structures and deprivation of nutrients
Observations of conidia germination with fluorescent microscopy up to 7 d pai showed that RS application delayed hyphae formation and subsequent conidiophore production when compared with the water treated plants (Fig. 1b)
We studied the effect of RS application on Powdery mildew (PM) progress in S and intermediate resistance (IR) courgette genotypes and described its mode of action

Summary

Introduction

Plants upon attack of pathogenic micro-organisms activate complex immune networks to prevent or minimize colonization of their internal structures and deprivation of nutrients. Apart from microbial infection, plant resistance mechanisms may be induced by a range of elicitors which are signal-inducing compounds or agents that trigger the innate immune system and prime and/or induce defense responses[2,3]. SA is a phenolic plant hormone that plays central role in plant defense against biotrophic pathogens[4] This natural defense phytohormone serves as an endogenous signal to activate certain immune responses and to establish disease resistance. There are substances (e.g. elicitors) that can enhance the efficacy of resistance by assisting a prompt and effective response under the challenge of a pathogen They are of particular interest as they allow targeted induction of plant resistance during periods of high disease pressure and/or plant susceptibility and thereby increase resource use efficiency. Various elicitors are commercially available and marketed as plant strengthening products (e.g. chitin, chitosan, etc.) or plant protection products (e.g. RS), our understanding of the molecular and biochemical mechanisms by which elicitors induce plant resistance and how this compares to genetically determined resistance/tolerance is still relatively limited

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