Hop Polyphenols in Relation to Verticillium Wilt Resistance and Their Antifungal Activity.

Sabina Berne,Branka Javornik,Sebastjan Radišek,Damijana Kastelec,Nataša Kovačević

doi:10.3390/plants9101318

Abstract

(1) Background: Verticillium wilt (VW) of hop is a devastating disease caused by the soil-borne fungi Verticillium nonalfalfae and Verticillium dahliae. As suggested by quantitative trait locus (QTL) mapping and RNA-Seq analyses, the underlying molecular mechanisms of resistance in hop are complex, consisting of preformed and induced defense responses, including the synthesis of various phenolic compounds. (2) Methods: We determined the total polyphenolic content at two phenological stages in roots and stems of 14 hop varieties differing in VW resistance, examined the changes in the total polyphenols of VW resistant variety Wye Target (WT) and susceptible Celeia (CE) on infection with V. nonalfalfae, and assessed the antifungal activity of six commercial phenolic compounds and total polyphenolic extracts from roots and stems of VW resistant WT and susceptible CE on the growth of two different V. nonalfalfae hop pathotypes. (3) Results: Generally, total polyphenols were higher in roots than stems and increased with maturation of the hop. Before flowering, the majority of VW resistant varieties had a significantly higher content of total polyphenols in stems than susceptible varieties. At the symptomatic stage of VW disease, total polyphenols decreased in VW resistant WT and susceptible CE plants in both roots and stems. The antifungal activity of total polyphenolic extracts against V. nonalfalfae was higher in hop extracts from stems than those from roots. Among the tested phenolic compounds, only p-coumaric acid and tyrosol markedly restricted fungal growth. (4) Conclusions: Although the correlation between VW resistance and total polyphenols content is not straightforward, higher levels of total polyphenols in the stems of the majority of VW resistant hop varieties at early phenological stages probably contribute to fast and efficient activation of signaling pathways, leading to successful defense against V. nonalfalfae infection.

Highlights

Verticillium wilt (VW), caused by plant pathogenic fungi from the Verticillium sensu stricto genus, is one of the most serious soil-borne diseases, estimated to affect nearly 400 plant species, ranging from herbaceous annuals to woody perennials [1]
The antifungal activity of total polyphenolic extracts against V. nonalfalfae was higher in hop extracts from stems than those from roots
Total polyphenols were extracted from dry samples of hop roots and stems, collected at phenological (BBCH) stages 51–55 and 87–89, and their concentration was determined spectrophotometrically [43]

Summary

Introduction

Verticillium wilt (VW), caused by plant pathogenic fungi from the Verticillium sensu stricto genus, is one of the most serious soil-borne diseases, estimated to affect nearly 400 plant species, ranging from herbaceous annuals to woody perennials [1]. The colonization of host plants occurs through the root epidermis and, if successful, the fungus spreads to the vascular tissues, leading to systemic infection of the plant [2]. The disease symptoms vary among hosts, they typically include wilting, chlorosis, necrosis, and vascular discoloration [1,2,3]. VW of hop was first reported in 1924 in England [6], where mild and lethal (progressive) disease forms were described [7] and attributed to the pathogen virulence, the sensitivity of the hop cultivars, and ecological. Genetic analysis and pathogenicity assays confirmed mild and lethal groups among V

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