Mário Lúcio Vilela de Resende

Espécies Ativas de Oxigênio na Resposta de Defesa de Plantas a Patógenos

Oxidative burst is a very quick plant defense response after pathogen recognition, leading to hypersensitive reaction (HR). This response is due to generation of reactive oxygen species (ROS), such as H2O2 , O2-, and OH-. Several roles in plant defense have been proposed for ROS. Hidrogen peroxide (H2O2), apart from being directly toxic to pathogens, is also involved in cell wall strengthening, since it is necessary for lignin biosynthesis. Hidrogen peroxide acts as a second messenger, being responsible for the activation of the benzoic acid 2-hydrolase, enzyme responsible for benzoic acid conversion to salycilic acid. Oxidative burst is not only confined to the macroscopic site of HR, since secondary bursts can occur in distant tissues, causing micro-HRs and leading to systemic acquired resistance (SAR), which is mediated by salycilic acid as a signal. Therefore, occurrence of both HR and SAR are dependent on signaling cascades derived from oxidative burst, as an early event in plant response against pathogen invasion.

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.

Atividades de quitinase e beta-1,3-glucanase após eliciação das defesas do tomateiro contra a mancha-bacteriana

The objective of this work was to assess the influence of foliar application of resistance inducers and the activation of plant pathogenesis-related (PR) proteins, chitinases and beta-1,3-glucanases, against Xanthomonas campestris pv. vesicatoria, and evaluate the potential of these elicitors on the reduction of bacterial leaf spot. Tomato plants of the cultivar Santa Cruz Kada were sprayed with: acibenzolar-S-methyl (0.2 g L-1 ASM); Ecolife, a biological formulation based on citric biomass (5 mL L-1); chitosan suspension from Crinipellis perniciosa mycelium (MCp; 200 g L-1); an aqueous extract from branches of lobeira (Solanum lycocarpum) infected with C. perniciosa (VLA; 300 g L-1). Plants were challenged with a virulent bacterial strain four days after spraying. Plants sprayed with the tested substances showed reduction of bacterial spot. ASM provided 49.3% protection, and was equal to MCp and Ecolife, and superior to VLA. VLA treatment did not differ statistically from MCp and Ecolife. Increases of beta-1,3-glucanase and chitinase activities were observed in treated plants at the first hour after spraying.

Acibenzolar-S-Metil e Ecolife® na indução de respostas de defesa do tomateiro contra a mancha bacteriana (Xanthomonas vesicatoria)

Foi investigada a eficacia comparativa da pulverizacao foliar em tomateiro de acibenzolar-S-metil (ASM) e Ecolife® na protecao contra Xanthomonas vesicatoria, bem como avaliada a ativacao de algumas respostas bioquimicas de defesa de planta. Plantas de tomateiro cv. Santa Cruz Kada foram pulverizadas com acibenzolar S-metil (0,2 g l-1 ASM) e uma formulacao natural proveniente de biomassa citrica denominada Ecolife® (5 ml l-1). Quatro dias apos as pulverizacoes, as plantas foram inoculadas com um isolado patogenico de Xanthomonas vesicatoria. Em experimentos de quantificacao de doenca, a pulverizacao foliar de Ecolife® e ASM conferiu 39,2% e 47,7% de protecao, respectivamente. A resistencia induzida em plantas pulverizadas com ASM e Ecolife® foi evidenciada pelo aumento da atividade de peroxidases (POX) e oxidases de polifenois (PPO), iniciado logo as primeiras horas apos as pulverizacoes, continuando ate 12 dias de avaliacao. A despeito da tendencia de queda nas atividades de amonia-liases de fenilalanina (PAL) a partir de 3 dias apos as pulverizacoes, plantas tratadas com ASM e Ecolife® tiveram discreto aumento no acumulo de lignina, principalmente aquelas pulverizadas com Ecolife® e inoculadas com X. vesicatoria. Teores de fenois soluveis totais decresceram significativamente, 9 e 12 dias apos pulverizacoes. O aumento nas atividades de POX e PPO poderia resultar em lignificacao, a qual estaria associada a uma estrategia de defesa do tomateiro contra a mancha bacteriana.

Rhizobacterium and acibenzolar-S-methyl (ASM) in resistance induction against bacterial blight and expression of defense responses in cotton

The effect of acibenzolar-S-methyl (ASM) and the rhizobacterium isolate L2-1 (Bacillus cereus), applied either alone or in combination, was evaluated in cotton plants for resistance induction against Xanthomonas axonopodis pv. malvacearum. Bacterial blight severity, lignin content and the activities of phenylalanine ammonia-lyase (PAL), peroxidase (POX) and b-1.3 glucanase (GLU) were assessed at different time courses. ASM and L2-1, used alone or in combination, significantly reduced disease severity, while ASM alone was the best treatment for bacterial blight control. No synergistic effect was observed when ASM was associated to isolate L2-1. ASM induced the highest increases in the activities of PAL, POX and GLU as well as lignin deposition, mainly 14 days after treatment application. When ASM and the rhizobacterium were simultaneously applied, enzyme activities were always lower, compared to ASM alone.

Effect of extracts from citric biomass, rusted coffee leaves and coffee berry husks on Phoma costarricencis of coffee plants

Phoma leaf spot, caused by Phoma costarricensis poses a serious threat to coffee (Coffea arabica) production, especially in the highlands of the state of Minas Gerais, Brazil. Extracts of citric biomass, coffee berry husks and coffee leaves severely affected by rust caused by Hemileia vastatrix, were evaluated against P. costarricensis. In an in vitro assay, aqueous extracts of rusted leaves and berry husks plus the commercial extracts based on citric biomass named Ecolife® and Agromil® were tested at various dilutions on the mycelial growth inhibition of P. costarricensis. In vivo, coffee seedlings maintained in glasshouse, were sprayed with these extracts seven days before inoculation of P. costarricensis. Only extracts from citric biomass had inhibitory effects on the fungus. In vivo, Ecolife® (5 ml/l), Agromil® (5 g/l) and the aqueous extract of rusted coffee leaves (dilution 1:6) reduced Phoma leaf spot. Both, Ecolife® and the extract of rusted coffee leaves were significantly more effective in reducing the area under the lesion progress curve when applied at lower doses, indicating a possible effect on the induction of resistance.

Fosfito de potássio na indução de resistência a Verticillium dahliae Kleb., em mudas de cacaueiro (Theobroma cacao L.)

Ha varios relatos da utilizacao de fosfitos no controle de doencas de plantas, por meio de acao direta, antifungica e indireta por inducao de resistencia. Essa atuacao como indutor e questionada, nao sendo encontradas, em muitos desses trabalhos, evidencias de respostas de defesa ativadas pelos sais de fosfito. Com o presente trabalho, objetivou-se estudar o efeito de doses (0,62; 1,25; 2,5 e 5 mL.L-1 de agua) de fosfito de potassio na inducao de resistencia em mudas de cacaueiro a V. dahliae, alem de investigar os possiveis mecanismos envolvidos na resposta de defesa. Foram realizados experimentos no Laboratorio de Fisiologia do Parasitismo e casa-de-vegetacao do Departamento de Fitopatologia UFLA. A aplicacao foliar do fosfito foi realizada 7 dias antes das inoculacoes e as avaliacoes de severidade foram realizadas aos 20, 30, 40, 50 e 60 dias apos a inoculacao. Foi realizado tambem um experimento para verificar o efeito toxico direto e outro para avaliar a atividade das enzimas peroxidases e polifenoloxidases e a concentracao de lignina. O tratamento com o fosfito de potassio (1,25 mL.L-1 de agua) proporcionou 10% de reducao na area abaixo da curva de progresso da severidade da murcha-de-Verticillium (AACPD), 60 dias apos aplicacao foliar, nao diferindo de nenhuma das doses, nem da testemunha. Todas as doses utilizadas apresentaram efeito fungitoxico, inibindo a germinacao de V. dahliae. A aplicacao do fosfito de potassio (1,25 mL.L-1 de agua) nao induziu aumento na atividade das enzimas peroxidases e polifenoloxidases em relacao a testemunha. Plantas tratadas com esse produto apresentaram um pequeno incremento na concentracao de lignina, nao apresentando diferenca significativa da testemunha absoluta.

Efeito de indutores de resistência em cafeeiro contra a mancha de Phoma

The effect of acibenzolar S-metil ester (ASM, Bion®), potassium phosfite (Hortifos PK®) and of a foliar fertilizer (Nutex Axcell®) was assessed on the spore germination and mycelial growth of Phoma costarricensis. The effect of these products on severity of Phoma leaf spot was also assessed on coffee seedlings. The percentage of conidial germination of P. costarricensis was not affected by doses of phosfite and ASM, but reductions on the mycelial growth of the fungus were detected. The area under the disease progress curve (AUDPC) and the disease severity were lower in all treatments compared to the inoculated control. There was a reduction of 50.9% on disease severity in plants treated with the standard fungicide tebuconazole. Low values for severity and AUDPC were observed when plants were treated with ASM 0.1 g/L; phosfite 2.5 mL/L; phosfite 5.0 mL/L and the fertilizer Nutex Axcell® at 4.0 mL/L, which differed from other treatments.

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.

Seleção de extratos vegetais para indução de resistência e ativação de respostas de defesa em cacaueiro contra a vassoura-de-bruxa

Objetivou-se encontrar novos indutores de resistencia contra a vassoura-de-bruxa (Crinipellis perniciosa) do cacaueiro (Theobroma cacao), com eficacia igual ou superior a aquela conferida pelo indutor de resistencia padrao, acibenzolar-S-metil, e estudar possiveis respostas de defesa ativadas no cacaueiro por esses eliciadores mais eficazes. Foram testados extratos de varias plantas, principalmente, nativas do cerrado mineiro, bem como extratos provenientes de outras especies cultivadas. Verificou-se que extratos aquosos produzidos a partir de ramos de lobeira (Solanum lycocarpum) com sintomas de vassoura-de-bruxa induziram protecao de mudas de cacaueiros contra a mesma doenca em nivel estatisticamente similar a protecao conferida pelo ASM. O extrato aquoso e fervido de lobeira, aqui denominado VLA, nao foi toxico in vitro, pelo contrario, induziu maior crescimento do fungo C. perniciosa em BDA, quando comparado a testemunha (crescimento em BDA puro). Quando se quantificou a atividade de proteinas relacionadas a patogenese (quitinase e b-1,3-glucanase) estimuladas por VLA e ASM (como padrao), observou-se que ambos os tratamentos induziram maiores atividades de peroxidase, quitinase e b-1,3-glucanase em mudas de cacaueiros, comparados as respectivas testemunhas, no periodo de 4 a 18 dias apos a pulverizacao (DAP). Tambem o teor de lignina aumentou em plantas tratadas com VLA ou ASM, principalmente aos 18 DAP.