Due to the lack of a standardized visual method for assessing bacterial blight (Pseudomonas syringae pv. garcae) in coffee leaves, a diagrammatic scale was developed and validated to quantify the disease. Leaves were collected in crops and nursery with different intensity of symptoms, and the true severity was determined electronically. Based on the frequency distribution of severity values and according to the Weber-Fechner's law of visual stimulus, the minimum and maximum limits and the intermediate levels in the scale were determined. Validation was performed by ten evaluators who estimated the severity of 50 leaves with different intensity of symptoms. One evaluation was performed without diagrammatic scale and two evaluations with the scale at 7-day intervals. The accuracy, precision, repeatability and reproducibility of the estimates were evaluated. The scale had nine levels: 0 (0%), 1 (0.1-0.99%), 2 (1-2%), 3 (2.01-4%), 4 (4.01-8%), 5 (8.01-16%), 6 (16.01-25%), 7 (25.01-45%) and 8 (≥45.1%). Using the scale, the evaluators were able to improve accuracy, precision, reproducibility and repeatability of estimates, compared to evaluators without scale. The scale was appropriate to visual estimation of severity of bacterial blight in coffee leaves.

Generally, the medicinal plants have antifungal substances that can be used for the plant protection against phytopathogens. The objective of this study was to know the efficiency of aqueous extracts from medicinal plants against the major etiological agents of coffee tree. The aqueous extracts used were extracted from bulbs of Allium sativum, leaves of Vernonia polysphaera, Cymbopogon citratus, Cymbopogon nardus, Cordia verbenacea, Eucalyptus citriodora, Ricinus communis, Azadirachta indica, Piper hispidinervum and flower buds of Syzygium aromaticum. The etiological agents considered for this study were Cercospora coffeicola, Colletotrichum gloeosporioides, Fusarium oxysporum, Phoma tarda, Rhizoctonia solani and Hemileia vastatrix. The screening for harmful extracts was done based on mycelial growth and conidial germination inhibition. All experiments performed were in vitro conditions. The inhibition of mycelial growth was performed mixing the extracts with the PDA. This mixture was poured in Petri dishes. On the center of the dishes was added one PDA disc with mycelium. It was incubated in a chamber set to 25ºC. The evaluation was done daily by measuring the mycelial growth. The germination assessment was also performed with Petri dishes containing agar-water medium at 2%. These were incubated at 25ºC for 24 hours. After this period the interruption of germination was performed using lactoglycerol. The experiments were conducted in a completely randomized design. The most effective plant extracts against the micelial growth and conidial germination were V. polysphaera, S. aromaticum and A. sativum. Keywords: Phoma tarda, Cercospora coffeicola, Colletotrichum gloeosporioides, Hemileia vastatrix, Phytopathology.RESUMO: Atividade antifúngica utilizando extratos de plantas medicinais contra fitopatógenos do cafeeiro. Geralmente, as plantas medicinais têm substâncias antifúngicas que podem ser utilizadas para a proteção das plantas contra fitopatógenos. O objetivo deste estudo foi conhecer a eficiência de extratos aquosos de plantas medicinais contra os principais agentes etiológicos do cafeeiro. Os extratos aquosos utilizados foram extraídos de bulbos de Allium sativum, folhas de Vernonia polysphaera, Cymbopogon citratus, Cymbopogon nardus, Cordia verbenacea, Eucalyptus citriodora, Ricinus communis, Azadirachta indica, Piper hispidinervum e botões florais de Syzygium aromaticum. Os agentes etiológicos considerados neste estudo foram Cercospora coffeicola, Colletotrichum gloeosporioides, Fusarium oxysporum, Phoma tarda, Rhizoctonia solani e Hemileia vastatrix. A triagem dos extratos foi realizada com base no crescimento micelial e na inibição da germinação de conídios. Todos os experimentos foram realizados em condições in vitro. A inibição do crescimento micelial foi realizada misturandose os extratos com PDA. Esta mistura foi vertida em placas de Petri. No centro das placas foi adicionado um disco de PDA com micélio. Incubou-se em câmara programada para 25°C. A avaliação foi feita diariamente através d...

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Given the damage and losses caused by bacterial blight of coffee (Pseudomonas syringae pv. garcae) (PSG) in coffee (Coffea arabica) seedling nurseries and lack of knowledge of the origin of the initial inoculum, the goal of this study was to determine whether coffee seeds can contain viable inoculum and spread bacterial inoculum. Seeds from plants with symptoms of bacterial blight of coffee were immersed in sterilized saline solution, and the crude extract obtained was inoculated in leaves of coffee seedlings. Leaves of plants inoculated with seed extract from symptomatic plants had symptoms of bacterial blight similar to those on leaves inoculated with reference isolate PSG. Seedlings inoculated with seed extract from asymptomatic plants showed no symptoms. Symptomatic leaves were submitted to exudate tests, and the etiologic agent was isolated in culture medium. The isolates with colonies morphologically similar to reference isolate PSG were selected and tested for hypersensitive reaction (HR) and pathogenicity to coffee seedlings. The isolates positive for HR and pathogenic to coffee also showed biochemical and molecular patterns equal to those of reference isolate PSG by the rep-PCR technique using Box primer. Thus, coffee seeds from plants with symptoms of bacterial blight can contain viable inoculum of P. syringae pv. garcae.