Search

Summary • The aim of this study was to determine whether guaiacol peroxidase (POX), superoxide dismutase (SOD) and catalase (CAT) activities are effective in the protection and recovery of cowpea (Vigna unguiculata (L.) Walp.) leaves exposed to a salt-induced oxidative stress. The salt treatment (200 mm NaCl) was imposed during six consecutive days and the salt withdrawal after 3 d (recovery treatment). Control plants received no NaCl treatment. • The salt treatment caused almost complete cessation of leaf relative growth rate in parallel with the transpiration rate. The restriction in leaf growth was associated with a progressive increase in membrane damage, lipid peroxidation and proline content. Salt withdrawal induced a significant recovery in both leaf growth rate and transpiration. Surprisingly, these prestressed/recovered plants showed only a slight recovery in leaf lipid peroxidation and membrane damage. • Leaf CAT activity experienced a twofold decrease only after 1 d NaCl treatment, and salt withdrawal had no effect on its recovery. SOD activity did not change compared with control plants. By contrast, POX activity significantly increased after 1 d NaCl treatment and showed a significant recovery to levels near to those of control. • In conclusion, it appears that the ability of cowpea plants to survive under high levels of salinity is not caused by an operating antioxidant system involving SOD, POX and CAT activities in mature leaves.

Elicitors activate the defense mechanism in plants to resist pathogens. Ulvans and glucuronans can act as elicitors, and their activity seems to be related to the sulfate groups, rhamnose and uronic acid monosaccharides. Chichá gum (CHG), which also contains rhamnose and uronic acid, was sulfated with chlorosulfonic acid/N,N-dimethylformamide and deacetylated with sodium hydroxide solution. The changes were confirmed by infrared spectroscopy. Carbon-13 NMR revealed that sulfation occurred in galactose and rhamnose units. The apples were sprayed with water (negative control), deacetylated chichá gum (DCHG), and sulfated chichá gum (SCHG). The activity of enzymes guaiacol peroxidase and polyphenol oxidases and the lignin content were compared with those under the action of a commercial elicitor, benzothiadiazole. DCHG, and especially SCHG, increased the activity of the two enzymes. Only fruits treated with SCHG showed a significant (p

Grapevine trunk diseases are among the most important limiting factors of worldwide viticulture. In this context, we aimed to verify the effect of chemical fungicides, biological agents and plant extracts on the control of Lasiodiplodia theobromae in pruning wounds and their physiological effects in cv. Syrah grapevines. Plant extracts (clove, cinnamon, garlic, rosemary and lemongrass), commercial fungicides (difeconazole, tebuconazole, mancozeb, sulfur, pyraclostrobin, fosetyl-Al, and azoxystrobin), chitosan, Trichoderma harzianum and Bacillus subtilis were used for the in vitro trials. The protection of pruning wounds in the potted vines was studied using fosetyl-Al, tebuconazole, Trichoderma harzianum, Bacillus subtilis, garlic extract and clove extract. The experiments were carried out through two vegetative cycles: 2015/2016 and 2016/2017. The length of wood discoloration, pathogen re-isolation percentage, fresh mass of the pruning material, peroxidase activity, fluorescence, chlorophyll index, phenological stages, shoot length and leaf area were evaluated. The treatments with clove, garlic extract, tebuconazole, pyraclostrobin, mancozeb, fosetyl-Al and B. subtilis reduced mycelial growth by more than 90%. In the grapevines, the use of T. harzianum decreased the re-isolation of L. theobromae, but no differences were verified for the other plant evaluations. We concluded that the use of T. harzianum would be a potential option for wound protection without altering the physiological aspects of cv. Syrah grapevines. Grapevine trunk diseases are among the most important limiting factors of worldwide viticulture. In this context, we aimed to verify the effect of chemical fungicides, biological agents and plant extracts on the control of Lasiodiplodia theobromae in pruning wounds and their physiological effects in cv. Syrah grapevines. Plant extracts (clove, cinnamon, garlic, rosemary and lemongrass), commercial fungicides (difeconazole, tebuconazole, mancozeb, sulfur, pyraclostrobin, fosetyl-Al, and azoxystrobin), chitosan, Trichoderma harzianum and Bacillus subtilis were used for the in vitro trials. The protection of pruning wounds in the potted vines was studied using fosetyl-Al, tebuconazole, Trichoderma harzianum, Bacillus subtilis, garlic extract and clove extract. The experiments were carried out through two vegetative cycles: 2015/2016 and 2016/2017. The length of wood discoloration, pathogen re-isolation percentage, fresh mass of the pruning material, peroxidase activity, fluorescence, chlorophyll index, phenological stages, shoot length and leaf area were evaluated. The treatments with clove, garlic extract, tebuconazole, pyraclostrobin, mancozeb, fosetyl-Al and B. subtilis reduced mycelial growth by more than 90%. In the grapevines, the use of T. harzianum decreased the re-isolation of L. theobromae, but no differences were verified for the other plant evaluations. We concluded that the use of T. harzianum would be a potential option for wound protection without altering the physiological aspects of cv. Syrah grapevines.

Over the last few years, considerable effort has been spent by Embrapa in the construction of a plant disease database representative enough for the development of effective methods for automatic plant disease detection and recognition. In October of 2016, this database, called PDDB, had 2326 images of 171 diseases and other disorders affecting 21 plant species. PDDB size, although considerable, is not enough to allow the use of powerful techniques such as deep learning. In order to increase its size, each image was subdivided according to certain criteria, increasing the number of images to 46,513. Both the original (PDDB) and subdivided (XDB) databases are now being made freely available for academic research purposes, thus supporting new studies and contributing to speed up the advances in the area. Both collections are expected to grow continuously in order to expand their reach. PDDB and XDB can be accessed in the link https://www.digipathos-rep.cnptia.embrapa.br/.

The efficacy of controlling bacterial spot in susceptible tomato plants by using a natural product was compared to a commercial resistance inducer. Plants were sprayed with (a) acibenzolar-S-methyl, ASM [Bion® 50 WG (0.2 g l−1)] and (b) a heterogeneous chitosan suspension (MCp) from Crinipellis perniciosa mycelium. Plants were challenged 4 d later with a virulent strain of Xanthomonas vesicatoria, under greenhouse conditions. In assessing disease, MCp-treated plants showed significant responses, reaching 87% of ASM protection performance against X. vesicatoria leaf spot. Tomato leaves exposed to MCp and ASM were assayed for pathogenesis-related enzymes, lignin deposition and soluble phenolic compounds. Induced resistance (IR) was evidenced by the enhancement of peroxidase (POX), polyphenol oxidase (PPO), and chitinase (CHI) activities at 1–72 h after spraying. These enzymes and phenylalanine ammonia-lyase (PAL) were also observed at 6, 9 and 12 d after spraying (DAS) interval. Treated and inoculated plants showed an increase in lignin deposition. The content of total soluble phenolic compounds decreased significantly by 9 and 12 DAS. The results suggest that (IR) was characterized by increased POX and PPO activities, improving lignification and, to a less extent, by CHI activity.

Summary In this study, we compare some antioxidative responses of leaves and roots associated to growth reduction in cowpea plants (Vigna unguiculata) during short-term salt stress and recovery. The salt treatment was imposed (200 mM NaCl) for six consecutive days and the salt withdrawal after 3 d. The salt treatment caused an almost complete cessation in the relative growth rate of both leaves and roots. Although NaCl withdrawal has induced an intense reduction in the Na+ content from the leaves and roots, the growth recovery was slight, after 3 d. The leaf lipid peroxidation was increased in salt-stressed plants and slightly reduced in recovered plants after 3 d. Surprisingly, in the salt-stressed roots it decreased markedly after 3 d treatment and in the pre-stressed/recovered roots it was restored to levels near to the control. In leaves, catalase (CAT) activity showed a rapid and prominent decrease after 1 d of NaCl treatment and salt withdrawal had no effect on its recovery. In contrast, the root CAT activity was not changed by effects of both NaCl and salt withdrawal, over time interval. Leaf superoxide dismutase (SOD) activity did not change in all treatments, whereas in roots it significantly decreased after 3 d of salt treatment and recovered after NaCl withdrawal. Contrasting to the other enzymes, the guaiacol-peroxidase activity increased in leaves and roots, reaching almost 200% of control values and it significantly decreased in both organs from the pre-stressed/recovered plants. In conclusion, cowpea roots and leaves present distinct mechanisms of response to lipid peroxidation and CAT and SOD activities during salt stress and recovery. However, these responses and/or the oxidative damages caused by reactive oxygen species were not related with the growth reduction.

This study investigated the induced defence responses and protective effects on susceptible tomato ( Lycopersicon esculentum Mill.) against Xanthomonas vesicatoria (Doidge) by a heat-treated aqueous extract (VLA) from dry necrotic tissue of ‘Lobeira’ ( Solanum lycocarpum St. Hil.) branches infected with the fungus Crinipellis perniciosa (Stahel) compared with acibenzolar- S -methyl (ASM), a commercial inducer of resistance. Plantlets were sprayed with VLA and ASM and challenged 4 days later with a virulent strain of X. vesicatoria , under greenhouse conditions. The disease severity, fresh weight of shoots, the activities of phenol peroxidase (POX), polyphenol oxidase (PPO), chitinase (CHI), phenylalanine ammonia-lyase (PAL), lignin deposition, and soluble phenolic contents were evaluated in the leaf tissues. Reduction of the bacterial spot severity was observed in plantlets treated with VLA which conferred 63% of the ASM protection. This protective effect and lesion reduction promoted by VLA were probably associated particularly with POX and PAL activities, lignin deposition on leaf tissues and, to a less extent, CHI activity.

The activities of antioxidant enzymes and photosynthetic responses were investigated in tomato (Lycopersicon esculentum L. var.) pre-treated by plant activators and inoculated by Xanthomonas vesicatoria. Plants were sprayed with acibenzolar-S-methyl, ASM [Bion® 50 WG (0.2 g l−1)] and aqueous extract from dry necrotic tissue flour (VLA) of ‘Lobeira’ (Solanum lycocarpum) bush. Four days later, the plants were challenged with a virulent strain of X. vesicatoria, under greenhouse conditions. Tomato leaves were then assessed to determine the activities of the main antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and ascorbate peroxidase (APX). A reduction of bacterial leaf spot severity was observed in plants treated by ASM (49.3%) and VLA (31.4%), without any in vitro inhibitory activity over the pathogen. Controls showed decreases in CO2 assimilation, transpiration, photosynthetic rates, and stomatal conductance. Water use efficiency and carboxylation efficiency were strongly affected in ASM- and VLA-treated, in comparison to controls and healthy plants. The tested substances induced increases in SOD and CAT activities in a delayed enzymatic response typical in compatible plant–pathogen interactions. Measured at daily intervals, activities of APX and POX were significantly ( ρ ⩽ 0.05 ) higher in treated plants than in controls, except for APX in ASM-treated plants where no difference was found when compared to controls. Only POX was clearly induced at the earlier stages after spraying the tomato plants with ASM or VLA. Our results suggest that late increases in antioxidant enzyme activities may play a role in mitigating oxidative damage in restoring the photosynthetic imbalance imposed by the expansion of bacterial lesions.

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 beta-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. O efeito do acibenzolar-S-metil (ASM) e do isolado rizobacteriano L2-1 (Bacillus cereus), aplicados isoladamente ou simultaneamente, foi avaliado em plantas de algodão na indução de resistência contra Xanthomonas axonopodis pv. malvacearum. A severidade da mancha angular, o conteúdo de lignina e a atividade das enzimas fenilalanina amônia liase, peroxidase e beta-1,3-glucanase foram avaliados periodicamente. O ASM e o isolado L2-1, utilizados isolada ou simultaneamente, reduziram significativamente a severidade da doença, sendo o ASM, o melhor tratamento para o controle da mancha angular. Não houve efeito sinergístico quando se utilizou o ASM simultaneamente com o isolado L2-1. O ASM proporcionou os maiores aumentos nas atividades das enzimas fenilalanina amônia liase, peroxidase e beta-1,3-glucanase e na deposição de lignina, principalmente aos 14 dias após a aplicação dos tratamentos. Quando o ASM e a rizobactéria foram aplicados simultaneamente, a atividade das enzimas foi sempre inferior ao tratamento em que o ASM foi aplicado isoladamente.

O objetivo deste trabalho foi avaliar o potencial de extratos fúngicos e vegetais na redução da murcha-de-verticílio do cacaueiro, as atividades da peroxidase e polifenoloxidase e o conteúdo de lignina. Mudas de cacaueiro foram pulverizadas com filtrado de micélio de Rhizopus sp. (FMR), quitosana de Rhizopus sp. (QMR) e Trichoderma sp. (QMT), extratos de casca in natura e seca de maracujá, extrato metanólico de casca seca de frutos de maracujá (MMS) e acibenzolar-S-metil (ASM - 0.2 mg mL-1) e sete dias depois, submetidas à inoculação de Verticillium dahliae. O ASM reduziu a murcha-de-verticílio em 38,0%, seguido dos extratos FMR, QMT, MMS e QMR, que apresentaram reduções em 22,8, 20,1, 19,2 e 15,7%, respectivamente, em relação à testemunha. Plantas pulverizadas com ASM ou FMR seguidas de inoculação apresentaram aumento da atividade de peroxidase aos oito dias após a pulverização, comparadas às respectivas testemunhas, com pico aos 18 dias após a pulverização. ASM e FMR aumentaram a atividade de polifenoloxidase aos quatro dias após a pulverização. Maiores concentrações de lignina foram obtidas em plantas tratadas com FMR e FMR seguido de inoculação. FMR é um potencial indutor de resistência para manejo de murcha-de-verticílio em cacaueiro. 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.

Objetivou-se encontrar novos indutores de resistência contra a vassoura-de-bruxa (Crinipellis perniciosa) do cacaueiro (Theobroma cacao), com eficácia igual ou superior a aquela conferida pelo indutor de resistência padrão, acibenzolar-S-metil, e estudar possíveis respostas de defesa ativadas no cacaueiro por esses eliciadores mais eficazes. Foram testados extratos de várias plantas, principalmente, nativas do cerrado mineiro, bem como extratos provenientes de outras espécies cultivadas. Verificou-se que extratos aquosos produzidos a partir de ramos de lobeira (Solanum lycocarpum) com sintomas de vassoura-de-bruxa induziram proteção de mudas de cacaueiros contra a mesma doença em nível estatisticamente similar à proteção conferida pelo ASM. O extrato aquoso e fervido de lobeira, aqui denominado VLA, não foi tóxico in vitro, pelo contrário, induziu maior crescimento do fungo C. perniciosa em BDA, quando comparado à testemunha (crescimento em BDA puro). Quando se quantificou a atividade de proteínas relacionadas à patogênese (quitinase e beta-1,3-glucanase) estimuladas por VLA e ASM (como padrão), observou-se que ambos os tratamentos induziram maiores atividades de peroxidase, quitinase e beta-1,3-glucanase em mudas de cacaueiros, comparados às respectivas testemunhas, no período de 4 a 18 dias após a pulverização (DAP). Também o teor de lignina aumentou em plantas tratadas com VLA ou ASM, principalmente aos 18 DAP. The objective of this study was to find new inducers of resistance against witches' broom disease (Crinipellis perniciosa) of cocoa (Theobroma cacao), with higher or equal efficacy to that conferred by the standard inducer acibenzolar-S-methyl and to study possible defense responses activated in cocoa by these more efficient elicitors. Extracts from several plants were tested, mainly those from native plants from the savannah of Minas Gerais State, as well as extracts from cultivated plants. It was verified that aqueous extracts from "lobeira" (Solanum lycocarpum) tree with symptoms of witches' broom induced protection of cocoa seedlings at similar levels as that conferred by ASM. The aqueous and boiled extract from "lobeira", here named VLA, was not toxic in vitro: in fact, it promoted C. perniciosa growth on PDA medium. The activities of pathogenesis-related proteins chitinase and beta-1,3- glucanase stimulated by VLA and ASM were assessed and it was verified that both treatments induced higher activities of peroxidase, chitinase and beta-1,3-glucanase in cocoa seedlings, compared to the respective controls, from 4 to 18 days after spraying (DAS). The lignin content also increased in plants treated with VLA or ASM, mainly at 18 DAS.

Foi investigada a eficácia comparativa da pulverização foliar em tomateiro de acibenzolar-S-metil (ASM) e Ecolife® na proteção contra Xanthomonas vesicatoria, bem como avaliada a ativação de algumas respostas bioquímicas 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 formulação natural proveniente de biomassa cítrica denominada Ecolife® (5 ml l-1). Quatro dias após as pulverizações, as plantas foram inoculadas com um isolado patogênico de Xanthomonas vesicatoria. Em experimentos de quantificação de doença, a pulverização foliar de Ecolife® e ASM conferiu 39,2% e 47,7% de proteção, respectivamente. A resistência induzida em plantas pulverizadas com ASM e Ecolife® foi evidenciada pelo aumento da atividade de peroxidases (POX) e oxidases de polifenóis (PPO), iniciado logo às primeiras horas após as pulverizações, continuando até 12 dias de avaliação. A despeito da tendência de queda nas atividades de amônia-liases de fenilalanina (PAL) a partir de 3 dias após as pulverizações, plantas tratadas com ASM e Ecolife® tiveram discreto aumento no acúmulo de lignina, principalmente aquelas pulverizadas com Ecolife® e inoculadas com X. vesicatoria. Teores de fenóis solúveis totais decresceram significativamente, 9 e 12 dias após pulverizações. O aumento nas atividades de POX e PPO poderia resultar em lignificação, a qual estaria associada a uma estratégia de defesa do tomateiro contra a mancha bacteriana.

Há vários relatos da utilização de fosfitos no controle de doenças de plantas, por meio de ação direta, antifúngica e indireta por indução de resistência. Essa atuação como indutor é questionada, não sendo encontradas, em muitos desses trabalhos, evidências 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 água) de fosfito de potássio na indução de resistência em mudas de cacaueiro a V. dahliae, além de investigar os possíveis mecanismos envolvidos na resposta de defesa. Foram realizados experimentos no Laboratório de Fisiologia do Parasitismo e casa-de-vegetação do Departamento de Fitopatologia UFLA. A aplicação foliar do fosfito foi realizada 7 dias antes das inoculações e as avaliações de severidade foram realizadas aos 20, 30, 40, 50 e 60 dias após a inoculação. Foi realizado também um experimento para verificar o efeito tóxico direto e outro para avaliar a atividade das enzimas peroxidases e polifenoloxidases e a concentração de lignina. O tratamento com o fosfito de potássio (1,25 mL.L-1 de água) proporcionou 10% de redução na área abaixo da curva de progresso da severidade da murcha-de-Verticillium (AACPD), 60 dias após aplicação foliar, não diferindo de nenhuma das doses, nem da testemunha. Todas as doses utilizadas apresentaram efeito fungitóxico, inibindo a germinação de V. dahliae. A aplicação do fosfito de potássio (1,25 mL.L-1 de água) não induziu aumento na atividade das enzimas peroxidases e polifenoloxidases em relação à testemunha. Plantas tratadas com esse produto apresentaram um pequeno incremento na concentração de lignina, não apresentando diferença significativa da testemunha absoluta. There are several reports concerning with the use of phosphites for controlling of plant diseases, through direct action, antifungal, and indirect, by resistance induction. The performance of phosphites as inducer of resistance is questioned, not finding in many of those papers, evidences of defense responses activated by these salts. The present work aimed at studying the effect of doses (0.62; 1.25; 2.5 and 5.0 mL.L-1 of water) of potassium phosphite on the protection of cocoa seedlings against V. dahliae, besides investigating the possible mechanisms involved in the defense response. Experiments were accomplished at the laboratory of Physiopathology and in a greenhouse at the Plant Pathology Department - UFLA. Foliar applications of phosphite were carried out 7 days before inoculation and severity assessments at 20, 30, 40, 50 and 60 days after inoculation. Experiments were also set to verify the toxic effect of phosphites and to evaluate the action of the enzymes peroxidases and polyphenoloxidases and the lignin content. The treatment with the potassium phosphite (1.25 mL.L-1 of water) provided only 10% reduction in the area under the disease progress curve (AUDPC), 60 days after spraying, not differing from none of the doses, nor from the dose zero. All the used doses presented antifungal effect, inhibiting the germination of V. dahliae conidia. The application of the potassium phosphite (1.25 mL.L-1 of water) did not induce increase in the activities of the enzymes peroxidases and polyphenoloxidases in relation to the control. Treated plants with that product presented a small increment in the lignin content, not presenting a significant difference to the absolute control.