Gilvaine Ciavareli Lucas

Potential of essential oils for the control of brown eye spot in coffee plants

Este trabalho avaliou o efeito in vitro de oleos essenciais extraidos de canela, citronela, capim-limao, cravo-da-india, arvore-de-cha, tomilho, nim e eucalipto na germinacao de conidios e no crescimento micelial de Cercospora coffeicola, a eficacia destes oleos no controle da cercosporiose-do-cafeeiro em mudas das cultivares Catucai 2SL, Catuai IAC 62 e Mundo Novo 379/19 em casa de vegetacao; e seus efeitos sobre os eventos iniciais de germinacao e infeccao do patogeno in vivo por meio de microscopia eletronica de varredura. Todos os oleos essenciais inibiram a germinacao dos conidios com o aumento das concentracoes. Os oleos de cravo-da-india, canela, nim, tomilho e capim-limao inibiram o crescimento micelial de C. coffeicola. Os oleos de canela e citronela foram os mais promissores no controle da cercosporiose em todas as cultivares. Em microscopia eletronica de varredura, os oleos de canela e citronela reduziram a germinacao e o desenvolvimento micelial in vivo de C. coffeicola oito e 16 horas apos a inoculacao, promovendo, em alguns casos, o extravasamento do conteudo celular. Oleos essenciais de canela e citronela reduziram a incidencia e a severidade da cercosporiose, alem de apresentar efeito toxico direto ao patogeno.

Ativação de defesa em cacaueiro contra a murcha-de-verticílio por extratos naturais e acibenzolar-S-metil

The objective of this work was to assess the potential of fungal and plant extracts on the reduction of Verticillium wilt of cocoa, the activities of the enzymes peroxidase and polyphenoloxidase, as well as the lignin content. Seedlings of cocoa were sprayed with the mycelial filtrate of Rhizopus sp. (FMR), chitosan from Rhizopus sp. (QMR) and Trichoderma sp. (QMT), extracts of fresh and dry passion fruit peel, methanolic extract from dry passion fruit peel (MMS) and acibenzolar-S-methyl (ASM - 0.2 mg mL-1) and, inoculed with Verticillium dahliae, seven days later. ASM reduced the cocoa Verticillium wilt in 38.0%. The extract FMR, QMT, MMS and QMR presented as well reductions of 22.8, 20.1, 19.2 and 15.7%, respectively, in comparison with the control. Plants sprayed with ASM or FMR followed by inoculation presented increase of peroxidase activity at the 8th day after spraying, compared to the respective controls, with peak at the 18th day after spraying. ASM and FMR increased polyphenoloxidase activity at the 4th day after spraying. Higher lignin concentrations were obtained in plants treated with FMR and FMR following by inoculation. FMR may constitute a potential resistance inducer for the management of the Verticillium wilt of cocoa.

Antibacterial activity of essential oils on Xanthomonas vesicatoria and control of bacterial spot in tomato

The objective of this work was to evaluate the effects of plant essential oils (EOs) on the growth of Xanthomonas vesicatoria, on bacterial morphology and ultrastructure, and on the severity of tomato bacterial spot. EOs from citronella, clove, cinnamon, lemongrass, eucalyptus, thyme, and tea tree were evaluated in vitro at concentrations of 0.1, 1.0, 10, and 100% in 1.0% powdered milk. The effect of EOs, at 0.1%, on the severity of tomato bacterial spot was evaluated in tomato seedlings under greenhouse conditions. The effects of citronella, lemongrass, clove, and tea tree EOs, at 0.1%, on X. vesicatoria cells were evaluated by transmission electron microscopy. All EOs showed direct toxic effect on the bacteria at a 10%-concentration in vitro. Under greenhouse conditions, the EOs of clove, citronella, tea tree, and lemongrass reduced disease severity. EOs of clove and tea tree, and streptomycin sulfate promoted loss of electron-dense material and alterations in the cytoplasm, whereas EO of tea tree promoted cytoplasm vacuolation, and those of citronella, lemongrass, clove, and tea tree caused damage to the bacterial cell wall. The EOs at a concentration of 0.1% reduce the severity of the disease. Resumo - O objetivo deste trabalho foi avaliar o efeito de oleos essenciais (OEs) no crescimento de Xanthomonas vesicatoria, na morfologia e na ultraestrutura bacteriana, e na severidade da mancha-bacteriana do tomateiro. OEs de citronela, cravo-da-india, canela, capim-limao, eucalipto, tomilho e arvore-de-cha foram avaliados in vitro nas concentracoes de 0,1, 1,0, 10 e 100% em leite em po a 1,0%. O efeito dos OEs, a 0,1%, na severidade da mancha-bacteriana do tomateiro foram avaliados em plantas de tomateiro em casa de vegetacao. Os efeitos dos oleos de citronela, capim-limao, cravo-da-india e arvore-de-cha, a 0,1%, nas celulas de X. vesicatoria foram avaliados por meio de microscopia eletronica de transmissao. Todos os OEs apresentaram efeito toxico direto sobre as bacterias na concentracao de 10% in vitro. Em casa de vegetacao, os OEs de cravo-da-india, citronela, arvore-de-cha e capim-limao reduziram a severidade da doenca. Os OEs de cravo-da-india e arvore-de-cha, e o sulfato de estreptomicina promoveram perda de material eletro-denso e alteracoes no citoplasma, enquanto o OE de arvore-de-cha promoveu vacuolizacao do citoplasma, e os de citronela, capim-limao, cravo-da-india e arvore-de-cha causaram danos a parede celular bacteriana. Os OEs, na concentracao de 0,1%, reduzem a severidade da doenca. Termos para indexacao: controle alternativo de doencas de plantas, ultraestrutura celular, bacteria fitopatogenica.

Essential oils for rust control on coffee plants

A ferrugem e considerada a doenca de maior importância no cafeeiro, pois causa acentuada desfolha nas plantas e, consequentemente, reducao na produtividade. Este trabalho avaliou o efeito in vitro de oleos essenciais de canela, citronela, capim-limao, cravo-da-india, arvore-de-cha, tomilho, nim e eucalipto na germinacao de urediniosporos de Hemileia vastatrix; a eficacia desses oleos no controle da ferrugem em mudas de cafeeiro das cultivares Catucai 2SL, Catuai IAC 62 e Mundo Novo 379/19 em casa de vegetacao; e o efeito dos oleos mais promissores sobre urediniosporos de H. vastatrix por meio de microscopia eletronica de transmissao (MET). Todos os oleos essenciais inibiram a germinacao dos urediniosporos com o aumento das concentracoes. Todos os oleos promoveram controle parcial da doenca em casa de vegetacao. No entanto, os oleos de tomilho, cravo-da-india e citronela, na dose de 1000 µL L-1, foram os mais eficazes no controle da doenca nas cultivares Catucai 2SL, Catuai IAC 62 e Mundo Novo 379/19, respectivamente. Nas imagens geradas em MET, observou-se que urediniosporos expostos aos oleos de cravo-da-india, citronela e tomilho apresentaram desorganizacao citoplasmatica e vacuolizacao celular, sendo esta mais pronunciada em urediniosporos expostos ao oleo de citronela. Os oleos de tomilho, cravo-da-india e citronela sao promissores no controle da ferrugem em cafeeiro.

Citronella essential oil in the control and activation of coffee plants defense response against rust and brown eye spot

The rust and brown eye spot are the main coffee diseases. The losses are due to intense defoliation of plants, which has reduced its production and longevity. The brown eye spot also occurs in fruits, with negative effects on the beverage quality. Some essential oils have presented promising results in the control of plant diseases, as an alternative to the use of fungicides. The objective of this study was to evaluate citronella essential oil in the control of rust and brown eye spot and in the activation of coffee plants defense responses. Twelve-month-old plants were sprayed with citronella oil 1000 µL L-1, acibenzolar-S-methyl 200 mg L-1 and tebuconazole fungicide 200 mg L-1. Plants were inoculated with Hemileia vastatrix and Cercospora coffeicola seven days later. The application was repeated after 30 days. Plants with five months were sprayed with the same treatments to assess the induced defense responses. Citronella oil controlled rust and brown eye spot with efficiencies of 47.2% and 29.7%, respectively, while tebuconazole presented control of 96.5% and 90.5%, respectively. Acibenzolar-S-methyl reduced brown eye spot by 55.9% and showed no significant control of rust. Citronella oil increased peroxidase and chitinase activities in five months coffee plants 336, and 24 and 336 hours after spraying, respectively. Acibenzolar-S-methyl increased peroxidase, chitinase and ββ-1,3-glucanase activities 192, 288 and 336; 24 and; 240 hours after spraying, respectively. The treatments did not increase accumulation of phenols, but a significant increase in lignin was observed in plants sprayed with citronella oil.

Essential oils and whole milk in the control of soybean powdery mildew

This research aimed to evaluate the potential of essential oils (EOs) and cows whole milk (CWM) in order to control soybean powdery mildew and to estimate the most effective concentrations of these natural products in reducing the disease severity on soybean plants. Three experiments were carried out: The first experiment evaluated and selected the most effective treatments to reduce the severity of soybean powdery mildew under greenhouse conditions; the second experiment evaluated the effect of CWM and EOs of citronella, lemongrass, eucalyptus, cinnamon and tea tree on the pathogen through the ultrastructure analysis of soybean leaflets infected by Erysiphe diffusa using the scanning electron microscope (SEM) and light microscope (LM) technology. In the third experiment, the most effective products were tested at several concentrations in order to define the most effective concentrations to reduce disease severity under greenhouse conditions. The treatments CWM (100mL L-1) and EOs of citronella, lemongrass and eucalyptus (1.0mL L-1), reduced the disease severity from 67 to 74%. Direct effects from all natural products tested on the structures of E. diffusa were demonstrated through the SEM and LM analysis. Concentrations at 1.5mL L-1 for EOs of citronella, lemongrass and eucalyptus and also at 180mL L-1 for the treatment CWM were the most effective against E. diffusa on soybean.