ABSTRACT
Lettuce bacterial leaf spot caused by Xanthomonas campestris pv. vitians is an aggressive disease that is difficult to control. So far there are no reports of the reaction of biofortified lettuce genotypes to different isolates of the bacteria. Thus, the objective was to evaluate the aggressiveness of X. campestris pv. vitians, as well as the reaction of biofortified lettuce genotypes to bacterial spot. Two experiments were performed in two distinct seasons (winter and summer), in greenhouse at the Vegetable Experimental Station of the Federal University of Uberlândia (UFU). The experimental design in both experiments was a randomized block design, in a factor scheme of 5 × 4 (five genotypes and four strains), with four repetitions. Were evaluated the severity and the area under the disease progress curve. In general, the biofortified lettuce 'Uberlândia 10000' was more resistant to most bacterial strains in the summer cultivation, and in the winter period UFU 'Crespa 206'. The commercial cultivar Robusta was the most susceptible to the strains during both seasons. The UFU E125 strain was the most aggressive for most genotypes in both seasons.
Subject(s)
Xanthomonas campestris/genetics , Lettuce/genetics , Genotype , VegetablesABSTRACT
Gherkin seeds usually show irregular physiological quality. Seed production requires fast and reliable tests to evaluate seed quality. Germination test is considered a recognized analysis method; however, seed technology has pursuit the improvement of vigor tests aiming the evaluation of seed's physiological potential. Thus, the objective of this work was to evaluate procedures to perform the test of accelerated aging and determine the physiological and sanitary potential of gherkin seeds. Four seed lots of cultivar Liso Calcuta were used in the study. To evaluate the initial physiological quality the water content was determined and germination and emergence tests, as well as indices of germination speed and emergence speed were used. The accelerated aging test was performed as traditionally and with saturated saline solution, with 48, 72 and 96 hours, at temperatures of 41oC and 45oC. After aging, the water content was determined, and seeds' germination and sanity tests were performed. The experiment was set under a completely random design in factorial 4x3x2 (lots x aging periods x temperatures). The standard accelerated aging test and the test with saturated saline solution at 41oC for 96 hours were efficient to evaluate the vigor of gherkin seeds. Saturated saline solution provides uniform water absorption and deterioration in gherkin seeds, allowing to discriminate seed lots in different vigor levels. The salinity test after accelerated aging with saline solution reduces the incidence of some fungi.
Subject(s)
Seeds/physiology , CucumisABSTRACT
Pectobacterium is a complex taxon of strains with diverse characteristics. It comprises several genera, including Erwinia, Brenneria, Pectobacterium, Dickeya, and Pantoea. Pectobacterium and Dickeya cause diseases in a wide range of plants, including potatoes, where they are causative agents of soft rot in tubers and blackleg in field-grown plants.Characterizing Pectobacterium species allows for the analysis of the diversity of pectinolytic bacteria, which may support control strategies for plant bacterial diseases. The aim of this study was to perform biochemical, physiological, and molecular characterizations of Pectobacteriumspp. from different sites and host plants. The isolated strains were characterized by the glucose fermentation test, Gram staining, catalase activity, oxidase activity, growth at 37 ºC, reducing substances from sucrose, phosphatase activity, indole production, acid production from different sources (sorbitol, melibiose, citrate, and lactose), pathogenicity in potato, and hypersensitivity reactions. Molecular characterization was performed with species-specific primers ECA1f/ECA2r and EXPCCF/EXPCCR, which identify P.atrosepticum and P.carotovorum subsp. carotovorum (Pcc), respectively, and with primers 1491f/L1RA/L1RG and Br1f/L1RA/L1RG that differentiate Pcc from Dickeya chrysanthemi and from P. carotovorum subsp. brasiliensis. The strains were identified as belonging to the genus Pectobacterium, though they did not fit the biochemical nor the molecular classification standards for subspecies differentiation, indicating significant diversity among the strains.
Pectobacterium é um táxon complexo de isolados bacterianos com características diversas. Compreende vários gêneros como Erwinia, Brenneria, Pectobacterium, Dickeya e Pantoea. Pectobacterium e Dickeya causam doenças em ampla variedade de plantas, incluindo a batateira, na qual são os agentes etiológicos da podridão mole dos tubérculos e da canela-preta de plantas cultivadas em campo.A caracterização de espécies de Pectobacterium permite a análise da diversidade de bactérias pectolíticas, podendo auxiliar estratégias de controle de doenças bacterianas em plantas. O objetivo deste trabalho foi caracterizar bioquímica, fisiológica e molecularmente isolados de Pectobacterium sp. provenientes de diferentes locais e hospedeiros. Os isolados foram caracterizados pelos testes de fermentação de glicose, Gram, catalase, oxidase, crescimento à 37 ºC, redução de substâncias a partir de sacarose, atividade da fosfatase, produção de indol, produção de ácido a partir de sorbitol, melibiose, citrato e lactose, patogenicidade em batata e reação de hipersensibilidade. Para a caracterização molecular, foram utilizados os pares de primersECA1f/ECA2r e EXPCCF/EXPCCR [específicos para P. atrosepticum e P.carotovorum subsp. carotovorum(Pcc), respectivamente] e as tríades de primers 1491f/L1RA/L1RG e Br1f/L1RA/L1RG, para diferenciar Pcc de Dickeya chrysanthemi e de P. carotovorum subsp. brasiliensis. Os isolados foram identificados como pertencentes ao gênero Pectobacterium, no entanto, não se enquadraram na classificação bioquímica e tampouco molecular para diferenciação das subespécies, demonstrando a grande diversidade dos mesmos.
Subject(s)
Solanum tuberosum , Polymerase Chain Reaction , PectobacteriumABSTRACT
Ralstonia solanacearum is a gram-negative soil-borne bacterium capable of infection of hundreds of vegetable species over more than 50 botanical families, causing bacterial wilt, except for bananas, when the disease is called Moko. It deserves special attention, from all other plant pathogenic bacteria, for its high phenotypic and genotypic plasticity, a characteristic that makes disease control extremely difficult. In this context, frequent and necessary surveys are conduct in the attempt of characterizing the prevailing strains of R. solanacearum in each region where the disease has been reported. However, knowledge about occurrence and diversity of R. solanacearum in Brazil is fragmented and in some cases, based on inconclusive studies with few strains, little representative of a given region. The need to obtain a greater picture guided this review. The occurrence of this bacterium in Brazilian States and the possible causes for its dissemination are presented, with emphasis on studies of genetic variability of populations of R. solanacearum in the country. The compiled results report a wide distribution of the bacterium in Brazil and great variability of its populations among locations. Partly due to the difficulty of detecting small titer of bacteria in samples, paucity of information about the origin of inoculum in certain regions is observed, as well as the need for detecting the presence of the pathogen in asymptomatic plants, potato tubers with latent infections, soil, and water, which are the major causes of bacterial dissemination into areas without any disease history.
Ralstonia solanacearum é uma bactéria gram-negativa habitante do solo capaz de infectar centenas de espécies vegetais distribuídas em mais de 50 famílias botânicas, onde causa a murcha-bacteriana, exceto na bananeira, na qual recebe o nome de Moko. Destaca-se entre outras bactérias fitopatogênicas pela sua alta plasticidade fenotípica e genotípica, característica que contribui sobremaneira para dificultar o controle da doença. Nesse contexto, levantamentos frequentes e necessários são conduzidos na tentativa de caracterizar isolados de R. solanacearum prevalentes em cada região onde a doença tem sido relatada. No Brasil, o conhecimento sobre a ocorrência e a variabilidade de R. solanacearum está fragmentado e, em alguns casos, baseado em estudos inconclusivos pelo uso de amostras de isolados pouco representativas de uma região. A necessidade de agrupar essas informações norteou a presente revisão de literatura. A ocorrência da bactéria nos Estados brasileiros e as possíveis causas de sua disseminação são apresentadas, com ênfase nos estudos da variabilidade genética das populações de R. solanacearum no país de acordo com o atual esquema de classificação da bactéria. Os resultados de pesquisa compilados da literatura reportam ampla distribuição da bactéria no Brasil e grande variabilidade de suas populações entre locais. Em parte devido à dificuldade de detectar pequenos números de células bacterianas em amostras, nota-se escassez de informações sobre a origem do inóculo em determinadas regiões, bem como a necessidade de detectar a presença do patógeno em plantas assintomáticas, em tubérculos de batata com infecções latentes, no solo e na água, que são as principais causas da disseminação da bactéria para áreas sem histórico da doença.
Subject(s)
Soil , Bacteria , Genetic Variation , Ralstonia solanacearumABSTRACT
The most effective disease management method for yield reducing diseases affecting tomatoes is the use of fungicides. This study evaluated the efficacy of chemical control on three Phytophthora sp. isolates, pathogenic to tomatoes. The effect of fungicides on mycelial growth of Phytophthora sp. and on tomato wilt was evaluated in vitro and in vivo. Two tests were done in Petri plates, and one on seedlings, in completely randomized design as a 4x3 factorial, with 5 replications. In vitro tests were done in growth chamber, at 25°C. The experimental unit consisted of a 5-mm diameter fungal mycelial plug placed 30 mm away from a filter paper disk, of similar size, soaked in fungicide, over cornmeal agar. The first test evaluated four commercial products registered for the control of potato blight: chlorothalonil+metalaxyl (Folio Gold® 742.5 WP); propamocarb chloridrate (Infinito® 687.5 CS), metalaxyl-m+mancozeb (Ridomil Gold® 68 WP), cymoxanil + manconzeb (Curzate® MZ 72 WG), at the recommended doses. The other assays evaluated three doses of Infinito (0.125%, 0.150% or 0.175%) and Ridomil. In vivo test was done in the greenhouse, and the experimental unit consisted of one pot, containing one tomato seedling, cultivar Alambra F1. Fungicide was drenched on the seedling soil one day prior to inoculation with 50,000 zoospores per pot. Data of mycelia growth inhibition by fungicide were submitted to analysis of variance and the averages compared by the Tukey test at 5% significance; efficacy was determined as a function of Ridomil®, the standard fungicide. In the first test, regardless of isolate, Infinito® presented performance similar to Ridomil® with efficacy of 98.5%, while Folio Gold® presented efficacy of 57.3% and Curzate® had no fungicide effect. Growth of isolate PP3 was smaller in all fungicides. In the second in vitro test, all three doses of Infinito® had efficacy above 82%. The best control was observed on isolates PP3 and PP4. In the third test, in vivo, no significant differences were observed in root matter among the standard fungicide and the doses of Infinito®; however, efficacy of Infinito® at 0.175% was 14% greater than that obtained with Ridomil®. It can be concluded that Infinito® is one more option for the control of tomato wilt.
O método mais efetivo no manejo das doenças fúngicas que afetam o tomateiro e reduzem a produtividade significativamente é o uso de fungicidas. Este trabalho avaliou a eficiência do controle químico sobre três isolados de Phytophthora sp. patogênicos ao tomateiro. O efeito de fungicidas no crescimento micelial de Phytophthora sp. e na murcha de tomateiro foi avaliado in vitro e in vivo, respectivamente. Foram realizados dois testes em placa de Petri e um teste em mudas, em delineamento experimental inteiramente casualizado (DIC), como fatorial 4x3, com 5 repetições. Os testes in vitro ocorreram em câmara de crescimento, a 25°C. A parcela experimental correspondeu a um disco de micélio fúngico disposto a 30 mm de um disco de papel embebido com solução de fungicida, ambos com 5 mm de diâmetro e dispostos sobre meio sólido a base de milho. O primeiro teste avaliou quatro produtos comerciais indicadas para o controle da mela ou requeima no tomateiro: clorotalonil+metalaxil (Folio Gold® 742,5 PM); propamocarbe (Infinito® 687,5 SC), metalaxil-M+mancozeb (Ridomil Gold® 68 PM), cimoxanil + manconzeb (Curzate® MZ 72 WG), nas dosagens recomendadas. Os demais ensaios avaliaram três doses de Infinito (0,125%, 0,150% e 0,175%) e Ridomil. O teste in vivo foi realizado em casa de vegetação, sendo a parcela experimental representada por um vaso, contendo uma muda de tomate, variedade Alambra F1. Fez-se "drench" para aplicação do fungicida no dia anterior à inoculação de 50.000 zoósporos por vaso. Dados de inibição do crescimento micelial por fungicidas foram submetidos à análise de variância e as médias comparadas pelo teste de Tukey a 5% de significância; e a eficácia foi calculada em função do Ridomil®, fungicida padrão. No primeiro ensaio, independentemente do isolado, Infinito® apresentou desempenho semelhante ao Ridomil® com uma eficácia de 98,5%, enquanto Folio Gold® apresentou eficácia de 57,3% e Curzate não apresentou efeito fungicida. O crescimento do isolado PP3 foi menor em todos os produtos. No segundo teste in vitro as três doses de Infinito® tiveram eficácia superior a 82%. O melhor controle foi observado sobre os isolados PP3 e PP4. No terceiro teste, in vivo, não houve diferença significativa na massa de raízes, entre o padrão e as doses de Infinito®, no entanto, a eficácia de Infinito® a 0,175% foi 14% maior que a obtida para o Ridomil®. Conclui-se que Infinito® é mais uma opção para controle da mela em tomateiro