Antifungal Activity of Propyl-Propane-Thiosulfinate (PTS) and Propyl-Propane-Thiosulfonate (PTSO) from Allium cepa against Verticillium dahliae: In Vitro and in Planta Assays.

Ana Falcón-Piñeiro,Enrique Guillamón,Alberto Baños,Miguel Noguera,Juan Antonio Navas-Cortes,Juan José Ariza,Efrén Remesal

doi:10.3390/jof7090736

Abstract

Verticillium wilt, caused by Verticillium dahliae, is the most devastating soil-borne fungal disease of olive trees worldwide. Currently, there is no effective measure available to control the pathogen in diseased plants in open field conditions. Searching more effective and sustainable solutions are a priority for the olive sector. The existing alternatives for disease control include the use of biological control microorganisms and compounds of natural origin from plants, such as Alliaceae. Propyl propane thiosulfinate (PTS) and propyl propane thiosulfonate (PTSO) are two organosulfur compounds derived from Allium cepa with a widely documented antimicrobial activity. The aim of this study was to evaluate the antifungal activity of PTS and PTSO against the defoliating and non-defoliating V. dahliae pathotypes. Firstly, several in vitro tests were performed (Minimum Antifungal Concentration, susceptibility studies according to the Kirby–Bauer disk-diffusion method, antifungal activity through aerial diffusion and effect on mycelial growth). The ability of both compounds to sanitize soil was evaluated using a sterile substrate inoculated with V. dahliae. Finally, challenges in growth chambers were carried out. PTS and PTSO generated growth inhibition zones in agar diffusion and the gas phase, and the mycelial growth of all the V. dahliae strains was significantly altered. The V. dahliae population in soil was considerably reduced after the sanitization. Finally, in planta assays demonstrated the ability of these compounds to reduce disease related parameters and their contribution to control the phytopathogen. In conclusion, the results showed that the PTS and PTSO from Allium cepa display in vitro and in vivo antifungal activity against V. dahliae and suggested that both compounds could be used as natural and environmentally friendly tools for Verticillium wilt management.

Highlights

The aim of the present study was to evaluate the antifungal activity of volatile organosulfur compounds propane thiosulfinate (PTS) and propane thiosulfonate (PTSO) from Allium cepa against the plant pathogenic fungi V. dahliae, both in vitro and in planta, and the determination of their potential use as soil sanitizer providing a new method to control Verticillium wilt in olive trees
The antifungal activity of organosulfur compounds PTS and PTSO has been evaluated against three different isolates of V. dahliae (Table 1)
Even though at the plant level, the D pathotype shows a greater virulence and lethality compared to the ND [3], our results showed no differences in the antifungal activity of PTS and PTSO between the D and ND isolates, neither in the disk-diffusion tests nor the Minimum Fungicidal Concentration (MFC) values obtained

Summary

Introduction

Verticillium wilt caused by fungus Verticillium dahliae is currently considered the main and most devastating soilborne fungal disease of olive trees (Olea europaea L.) [1]. It affects more than 400 plant species, such as cotton, tomato, almond and peach, the high incidence of this disease in all Mediterranean olive-growing regions is threating olive trees and olive oil production, causing important economic losses [2]. The D pathotype can be lethal to the plant and causes the extensive and early drop of infected green leaves and, eventually complete defoliation and necrosis. Trees infected by the ND pathotype can show complete remission from symptoms [3]

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