Comparison of efficacy and modes of action of two high-potential biocontrol &lt;i&gt;Bacillus&lt;/i&gt; strains and commercial biocontrol products against &lt;i&gt;Botrytis cinerea&lt;/i&gt; in table grapes

Héctor Calvo,Jean Roudet,Marc Fermaud,María Eugenia Venturini,Ana Pilar Gracia

doi:10.20870/oeno-one.2021.55.3.4688

Abstract

In table grapes (cv. Thomson Seedless), the antifungal activity against Botrytis cinerea was further analysed and compared between two high potential bacterial biological control agent (BCA) strains, Bacillus velezensis BUZ-14 and B. ginsengihumi S38. Two commercial biocontrol products (BPs), served as standards of comparison, Amylo-X® and Serenade Max®, also based on Bacillus BCA strains. The main mode of action quantified for all the strains was antibiosis due to hydrosoluble and volatile metabolites and their combinations. The BUZ-14 strain was the most active BCA strain, demonstrating significant disease reduction exceeding 60 % when used in the culture form grown in 863 medium, including living cells (LCs) and cell-free supernatant (CFS). Both BPs exhibited significantly reduced efficacy of their CFS fraction (< 10 %) compared with that of the two BCA strains, confirming their high antibiosis potential. The novel methodology allowed us to demonstrate the significant effect of the BCA culture medium on volatilome (VOC) antagonist efficacy. The S38 strain achieved the highest disease reduction (90 %) owing to the greatest production of VOCs in the richest MOLP (Medium Optimum Lipopetide Production) culture medium, whereas grape juice was the least favourable medium for VOC efficacy for both bacterial strains (BUZ14 and S38). The overall poor activity of living Bacillus cells in all the BCA and BPs tested is discussed based on the low capacity of the BCA strains to grow in the berry. Then, the presence of living cells is also discussed with the possibility that these cells are not required in field applications of such BCA strains in this genus. Moreover, different environmental suboptimal conditions, including temperature (22 and 27 °C) and relative humidity (RH) (100 and 85–95 %), were tested, and BUZ-14 exhibited the highest Botrytis reduction at both temperatures and RH values. However, no significant differences were observed between temperatures or RH values for the same BCA. Further studies in vineyard conditions and applications, such as biofumigation or active packaging, will be performed to confirm the new findings reported in this investigation.

Highlights

Botrytis cinerea is the causal agent of grey mould, which is one of the most important and damaging diseases affecting wine grapes and table grapes worldwide
To better characterise and rank the major mode(s) of action (MOAs) of the four bacterial strains tested based on efficacy, the antagonist efficacy was quantified for culture (Cul), living cells (LC), cell-free supernatant (CFS) and volatile organic compounds (VOCs)
This analysis was necessary to elucidate whether the antifungal activity against B. cinerea was mostly due to secondary metabolites produced during the bacteria premultiplication process, by living cells when directly interacting with the pathogen at the fruit surface, or both possibilities (Figure 2)

Summary

Introduction

Botrytis cinerea is the causal agent of grey mould, which is one of the most important and damaging diseases affecting wine grapes and table grapes worldwide. Most of the specific anti-Botrytis synthetic fungicides are responsible for relatively frequent contamination of commercial wines according to Esteve-Turrillas et al (2016). The use of these anti-Botrytis fungicides represents an issue of worldwide relevance with potentially negative consequences for consumer health and international trade

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