Essential plant oils in reducing the intensity of soft rot in Chinese cabbage

Rosa de Lima Ramos Mariano,Elineide Barbosa de Souza,Yrlânia de Lira Guerra,Myrzânia de Lira Guerra

doi:10.1590/s1806-66902014000400014

Abstract

The action of essential oils in reducing soft rot in Chinese cabbage, and their influence on the colorimetry and physicochemical characteristics of the vegetable were evaluated. In the greenhouse, plants of the cultivar Natsume were sprayed with 11 oils selected in preliminary tests for phytotoxicity: bergamot, lemongrass, copaiba, Eucalyptus citriodora, blue gum, fennel, ginger, spearmint, sweet orange, lemon and clary sage (0.5%) and also the antibiotic Mycoshield ® (3 g L -1 ). After 72 hours the plants were inoculated with Pectobacterium carotovorum subsp. carotovorum (Pcc-c). The oils and the Mycoshield ® significantly reduced (Pi 0.05) the severity (SEV) and the area under the disease progress curve (AUDPC). The oils of bergamot, copaiba, E. citriodora, spearmint and sweet orange were then tested for the stability of their effectiveness in the control of three isolates of P. carotovora subsp. carotovorum. These oils reduced the SEV (30.5 to 38.6%) and the AUDPC (23.1 to 26.6%) with no differences between them or the Mycoshield ® (SEV 45.2 and AUDPC 32.8%), except for the copaiba (20.3%) which was less effective than the antibiotic in the reduction of the AUDPC. In vitro, only Mycoshield ® inhibited the pathogen. None of the treatments altered the colorimetry, levels of ascorbic acid or pH of the leaves of the Chinese cabbage. The spearmint oil increased the total titratable acidity in the same way as the oils of sweet orange, E. citriodora and bergamot increased the total soluble solids. Therefore, spraying with the oils of bergamot, copaiba, E. citriodora, spearmint and sweet orange has potential in the control of this disease.

Highlights

In the state of Pernambuco in Brazil, Chinese cabbage (Brassica pekinensis L.) is a vegetable which is grown mainly in the Mata and the Agreste regions, with the municipalities of Vitória de Santo Antão and ChãGrande standing out as the main producers (CENTRO DEABASTECIMENTO E LOGÍSTICADE PERNAMBUCO, 2013)
Control of soft rot is hampered by the wide range of hosts of P. carotovorum subsp. carotovorum, its long period of survival in crop residues in the soil (REN; PETZOLDT; DICKSON, 2001; SILVA et al, 2012)
Given that in some areas of the state of Pernambuco soft rot is a limiting factor in the production of Chinese cabbage and that effective measures to control the disease are difficult to implement, the aims of this work were to evaluate the action of essential oils in the control of soft rot in Chinese cabbage and verify the effect of these products on the colorimetry and physicochemical characteristics of the vegetable

Summary

Introduction

In the state of Pernambuco in Brazil, Chinese cabbage (Brassica pekinensis L.) is a vegetable which is grown mainly in the Mata and the Agreste regions, with the municipalities of Vitória de Santo Antão and ChãGrande standing out as the main producers (CENTRO DEABASTECIMENTO E LOGÍSTICADE PERNAMBUCO, 2013). In the state of Pernambuco in Brazil, Chinese cabbage (Brassica pekinensis L.) is a vegetable which is grown mainly in the Mata and the Agreste regions, with the municipalities of Vitória de Santo Antão and Chã. In an epidemiological survey carried out in 22 areas of the Agreste region of Pernambucano where the Chinese cabbage is grown, the disease was found to have 100% prevalence, with an incidence ranging from 1 to 67% (SILVA et al, 2007). Control of soft rot is hampered by the wide range of hosts of P. carotovorum subsp. The high variability of the pathogen (ALVARADO et al, 2011) Recommended agricultural practices, such as the eradication of diseased plants, destruction of crop residues and the rotation of crops with grasses, are little used and are replaced by chemical control, which is generally inefficient. Despite there being no registered products, this being a ‘minor crop’, farmers use inappropriate products (MELLO et al, 2011) such as those from copper, for example

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