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With the growing demand for sustainable and safe agricultural practices, plant compounds emerge as a solution for biological activities. Here, we evaluated the potential of using Morinda citrifolia essential oil to induce plant resistance and to control phytopathogens (Curvularia lunata) and insect pests (Daubulus maidis). We conducted a chromatographic analysis to unveil the essential oil components. We also quantified the activity levels of antioxidant enzymes and chitinase for resistance induction. The antifungal action was evaluated through disease progression and the inhibition of mycelial growth in addition to in silico studies that made it possible to predict the interaction site between the fungal protein and the compounds. We assessed the toxicity and repellent actions towards the D. maidis. Octanoic acid (58.43%) was identified as the essential oil major compound. Preventive treatment with essential oil and octanoic acid (25.0 µL mL-1) increased not only the plant defense activities (i.e., the activity of the enzymes superoxide dismutase, catalase, phenol peroxidase, ascorbate peroxidase, and chitinase) but also controlled Curvularia leaf spot. The stable interactions between octanoic acid and tyrosine-tRNA ligase from C. lunata suggested protein synthesis inactivation. The essential oil inhibited 51.6% of mycelial growth, and this effect was increased to 75.9% with the addition of adjuvants (i.e., angico gum). The essential oil reduced 76% of the population of D. maidis adults and repelled 50% of the number of D. maidis after 48 h under field conditions. The repellency effect in the field reduced the population of D. maidis adults, transmitters of the stunting complex, by 50%. The results highlight the potential of M. citrifolia as a resistance activator, fungicide, insecticide, and an effective biorational alternative.

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Fumonisins are mycotoxins (MTs) produced mainly by the fungus Fusarium verticillioides, the main pathogens of maize which cause ear rot. The aim of this work was to evaluate some factors that may lead to high fumonisin production by F. verticillioides in maize grains, correlating the pathogen inoculation method with different genotypes grown in four Brazilian states. Experiments were conducted in 2015-2016 in maize crops from experimental maize fields located in four distinct states of Brazil. Results showed that contamination by fumonisin mycotoxins occurred even on symptomatic or asymptomatic grains. In all municipalities, the samples showed levels of fumonisin B1 that were higher than would be tolerable for the human consumption of corn products (the current tolerance limit for fumonisin is 1.5 µg g-1). High severity of grains infected with F. verticillioides does not always show high concentrations of fumonisins. Environments with higher temperatures may influence the production of high concentrations of fumonisin in maize hybrids. Spray inoculation methods and inoculation at the center of spikes did not influence fumonisin concentrations. Results showed that the hybrids P3630H, P32R48 and P3250 presented higher disease severity, as well as higher mycotoxin levels in the studied locations with higher temperatures.

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The objective of this work was to evaluate the efficiency of noni essential oil on the control of Exserohilum turcicum, a causative agent of Exserohilum spot in maize culture. In the sanitary test 400 seeds were incubated using the blotter test method. For the transmissibility test, the fragments of damaged leaves of seedlings were removed and put into a potato, dextrose and agar (PDA) culture environment. To verify the pathogenicity, Koch´s postulates were performed. In the phytotoxicity test different concentrations of noni oil were applied in maize seedlings. E. turcicum conidia were submitted to different concentrations of noni oil. In the preventive and curative tests noni essential oils were applied before and after the conidia inoculation, respectively. The results revealed the presence of fungi of the genres Aspergillus, Penicillium, Rhizopus, Fusarium, and Exserohilum in the maize seeds. The pathogenicity of E. turcicum and also the transmission of this fungus from the seeds to the maize seedlings was confirmed. The inhibition of conidia germination was proportional to the concentration increase. The preventive application of noni essential oil was the most efficient on the control of Exserohilum spot.

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The Curvularia Leaf Spot is becoming more common due to the culture expansion and the low resistance of the cultivated genotypes in tropical regions. Thus, the objective was to evaluate the fungitoxicity of the essential oil of Cymbopogon citratus upon the phytopathogen Curvularia lunata, causative agent of the Curvularia Leaf Spot. There was realized pathogenicity tests of C. lunata in maize plants, phytotoxicity of the essential oil of C. citratus and gas chromatography attached, germination tests of the conidia, and of in vitro inhibition of C. lunata. Also, there were realized tests aiming at verifying the phytopathogen control in vivo. In the pathogenicity tests, there were verified symptoms of the disease in all of the suspensions tested on plants. It was observed that the essential oil concentrations of 7.5 µL mL-1 to 50 µL mL-1 were phytotoxic. The majoritarian chemical components of the essential oil of C. citratus were Geranial (41.46%) and Neral (32.43%). The concentrations of 5 and 7.5 µL mL-1 inhibited 100% of conidia germination. None of the concentrations evaluated effectively inhibited C. lunata mycelial growth in in vitro tests. In the preventive control, the concentration of 7.5 µL mL-1 was sufficient for the reduction of the progress of the disease, however the curative control was not efficient on the tested dosages.

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Gummy stem blight, caused by Didymella bryoniae (Auersw.) Rehn, is a disease that affects the productivity of watermelon leading to losses exceeding 40%. This study aimed at evaluating the efficiency of different production systems in the control of watermelon gummy stem blight in order to establish effective methods to combat the disease. The following treatments were applied: conventional management, integrated management and organic production. Mineral fertilizer was applied to conventional and integrated management, whereas in organic production was used the cattle manure. There was application of fungicides and insecticides in commercial doses in conventional and integrated management, and the application was according to monitoring in integrated management. No fungicide or insecticide was applied to organic production. The disease severity was assessed by rating scale. The experimental design was randomized blocks. The severity of gummy stem blight increased substantially during fruit formation. Watermelon plants grown with integrated management showed lower levels of disease severity, while plants in organic production exhibited higher severity levels. We conclude that the management based on judicious monitoring in field is the best way to attain appropriate phytosanitary quality for the watermelon crop in Tocantins State, Brazil.

A podridão gomosa (Didymella bryoniae) é uma doença que afeta a produtividade da melancia levando a perdas superiores a 40%. Objetivou-se avaliar a eficiência de diferentes sistemas de produção no controle da podridão gomosa em melancia visando estabelecer métodos eficientes de combate à doença. Aplicou-se os seguintes tratamentos: manejo convencional, manejo integrado e cultivo orgânico. A adubação mineral foi aplicada em manejo convencional e no manejo integrado, enquanto que no cultivo orgânico foi utilizado o esterco bovino. Houve aplicação de fungicidas e inseticidas em doses comerciais no manejo convencional e manejo integrado, sendo que no manejo integrado a aplicação foi conforme monitoramento. A severidade da doença foi avaliada por escala de notas. O delineamento experimental foi blocos ao acaso. A severidade da podridão gomosa aumentou substancialmente na fase de formação dos frutos. Plantas de melancia cultivadas com o manejo integrado apresentaram menores níveis de severidade da doença, enquanto as plantas em cultivo orgânico exibiram maiores níveis de severidade. Conclui-se que o manejo baseado em acompanhamentos criteriosos em campo representa a melhor maneira de atingir o aspecto fitossanitário adequado para o cultivo de melancia no Estado do Tocantins, Brasil.

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O crestamento gomoso do caule, causado pelo fungo Didymella bryoniae, é uma doença comumente encontrada na melancia cultivada em vários países. No Brasil, são inúmeras as pesquisas relacionadas à doença, porém não há métodos padronizados de quantificação da severidade da doença em campo. Assim, foi desenvolvida uma escala diagramática com base em padrões de fotos digitalizadas de folhas de melancia infectadas com D. bryoniae. A escala desenvolvida apresentou níveis de 0; 10; 20; 45; 65 e 90% de severidade. A validação da escala foi dividida em duas partes: inicialmente, 10 avaliadores (metade com experiência e a outra metade sem experiência) estimaram a severidade da doença com base na observação inicial de 100 fotos de folhas de melancia com sintomas da doença em diferentes níveis de severidade. Em seguida, os mesmo avaliadores estimaram a severidade da doença com o auxílio da escala confeccionada a partir do programa Quant. Os dados foram analisados a partir de regressão linear e obtidos os coeficientes angular, linear e de correlação. A partir dos dados obtidos, determinou-se a acurácia e precisão das avaliações. Os coeficientes de determinação (R2) variaram entre 0,88 - 0,97 para os avaliadores experientes e de 0,55 - 0,95 para os avaliadores inexperientes. O coeficiente angular (A) médio para os avaliadores inexperientes foi de 20,42 e 8,61 sem e com o auxílio da escala diagramática, respectivamente. Os avaliadores experientes apresentaram valores de A médios de 5,30 e 1,68 sem e com o uso da escala diagramática, respectivamente. A análise dos erros absolutos indicou que o uso da escala diagramática contribuiu para minimizar as falhas na estimativa dos níveis de severidade. A escala diagramática proposta mostrou-se adequada para avaliação da severidade do crestamento gomoso do caule em melancia.

The gummy stem blight, caused by the fungus D. bryoniae, is a disease commonly found in watermelon cultivated in several countries. In Brazil, there are numerous studies related to the disease, but there are not uniform methods for quantifying of disease severity in the field. Thus, we developed a diagrammatic scale based on scanned photos of watermelon leaves infected with D. bryoniae. The scale developed showed levels of 0; 10; 20; 45; 65 and 90% of severity. The scale validation was divided into two parts: initially, 10 evaluators (half with experienced and other half without experience) estimated the disease severity based on the initial observation of 100 photos of watermelon leaves with symptoms of the disease at different severity levels. Before, the same evaluators estimated the disease severity with the support of the scale prepared from the Quant program. Data were analyzed using linear regression and were obtained angular, linear, and correlation coefficients. Based on these data, we determined the accuracy and precision of the evaluations. The correlation coefficients (R2) ranged from 0.88 - 0.97 for the experienced evaluators and from 0.55 - 0.95 for the inexperienced evaluators. The average angular coefficient (A) for inexperienced evaluators was 20.42 and 8.61 with and without the support of diagrammatic scale, respectively. Experienced evaluators showed values of average linear coefficient of 5.30 and 1.68 with and without the support of diagrammatic scale, respectively. The absolute errors analysis indicated that the use of diagrammatic scale contributed to minimize the flaws in the severity levels estimation. The diagrammatic scale proposed shown adequate for gummy stem blight severity evaluation in watermelon.

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