Antifungal activity of essential oil from Eucalyptus staigeriana against Alternaria alternata causing of leaf spot and black rot in table grapes.

Alternaria alternata causes leaf spot and black rot diseases in leaves and grapes of grapevines, respectively, and leads to huge economic losses in table grapes production. As natural antifungal agents, essential oils (EOs), which are generally recognized as safe substances, shows strong antifungal activity against fungal phytopathogens. The aim of this study was to determine the chemical composition of Eucalyptus staigeriana EO and its in vitro and in vivo effects against A. alternata. The major compounds of E. staigeriana EO were citral (34.32%, of which 21.83% geranial and 12.49% neral), limonene (20.60%) and 1,8-cineole (12.33%). E. staigeriana EO exhibited the highest inhibitory activity on mycelial growth and conidial germination at 1 µL mL-1. Moreover, the EO was able to reduce the incidence and severity of leaf spot disease in leaves and black rot disease in table grapes caused by A. alternata. These results represent a possible alternative to reduce the use of synthetic molecules for the control of diseases in postharvest of table grapes and in vineyard.

Essential oil as sustainable alternative for diseases management of grapes in postharvest and in vineyard and its influence on wine.

This study aimed to determine the chemical composition of Eucalyptus staigeriana essential oil (EO) and its effect in vivo against Botrytis cinerea and Colletotrichum acutatum in postharvest of grapes and in a vineyard. Moreover, grapes collected from de field experiments were used to evaluate the impact of the alternative control on the alcoholic fermentation and wine composition. The major compounds of E. staigeriana EO were citral (30.91%), 1,8-cineole (24.59%), and limonene (19.47%). In the postharvest experiment, EO was efficient, reducing the incidence and severity of disease caused by B. cinerea and the incidence of disease caused by C. acutatum, both in preventive and curative treatment. Moreover, this EO reduced the incidence and severity of gray rot caused by B. cinerea and the severity of ripe rot caused by C. acutatum in the field. The alternative control did not significantly influence the alcoholic fermentation and volatile composition of wines, except for the residual presence of 1,8-cineole that can contribute to the aroma complexity of 'Isabella' wine. These results are promising and indicate that E. staigeriana EO might be further investigated as a natural alternative to control fungal rots on grapes.

Alternative control of grape rots by essential oils of two Eucalyptus species.

BACKGROUND: Essential oils (EOs) are volatile natural compounds produced by plant secondary metabolism, and some of them exhibit antimicrobial activity. The objective of the present study was to determine the chemical composition the EOs of Eucalyptus staigeriana and Eucalyptus globulus, and their effect in vitro and in vivo against Botrytis cinerea and Colletotrichum acutatum, the most important fungal rot diseases of grapes. Moreover, grapes collected from field experiments were used to evaluate the impact of the alternative control on the alcoholic fermentation and wine composition. RESULTS: The major compound of E. staigeriana EO were citral 30.91% (19.74% geranial, 11.17% neral), 1.8-cineole (24.59%) and limonene (19.47%), while 1.8-cineole represented 68.26% of E. globulus EO. The two EOs showed in vitro antifungal activity against both pathogens. Eucalyptus staigeriana EO exhibited the highest activity inhibiting mycelial growth (MG) and conidial germination at 0.5 µL mL-1 . Moreover, this EO was able to reduce the incidence and severity of grey rot caused by B. cinerea and the severity of ripe rot caused by C. acutatum The alternative control did not significantly influence alcoholic fermentation, the physicochemical characteristics, and the volatile composition of wines. CONCLUSION: These results are promising and indicate that E. staigeriana EO might be further investigated as a natural alternative for the control of fungal rots on wine grapes. © 2019 Society of Chemical Industry.