Resumo em Inglês:

Common bean is an economically, nutritionally, and socially important crop. It is grown in distinct regions and different seasons around the world by subsistence level farmers with low-technology input as well as by farmers that use high input technologies. One important factor that can limit the bean growing and drastically affect grain yields is the high number of destructive pathogens that attack and cause serious damage to the crop. Among them is bean rust, incited by the fungus Uromyces appendiculatus. This disease is distributed throughout the world, but it effectively causes major production problems in humid tropical and subtropical regions. In Brazil, rust causes major losses in south, southeast, and central regions of the country. Bean rust control by resistant cultivars is an easy and economical strategy to be used in association to other rust management practices. Pyramiding of different race-specific resistance genes in association with other genes conferring adult plant resistance, slow rusting, and reduced pustule size can prolong the lifespan of a common bean cultivar by creating a more durable resistance complex against the rust pathogen. This review manuscript presents an overview on bean rust and reports some breeding efforts aiming to develop rust resistant cultivars in Brazil.

Resumo em Inglês:

Meloidogyne exigua is a plant-parasitic nematode that causes great losses to coffee farmers. Thus, to contribute to the development of new products to control this parasite, the present work studied the effect of volatile organic compounds (VOC) on the nematode and coffee plants (Coffea arabica), since these compounds are known to be used in plant defense against other agronomical pests. The number of galls of M. exigua was reduced when the aerial part of coffee plants was sprayed with combinations of methyl jasmonate + jasmone, (Z)-hex-3-en-1-ol + (E)-hex-3-en-1-ol + (Z)-hex-2-en-1-ol + (E)-hex-2-enal, (E)-hex-2-enyl acetate + hexyl acetate, meso-butane-2,3-diol + butane-1,2-diol + butane-1,3-diol + butane-1,4-diol, 3-hydroxybutan-2-one + 4-hydroxybutan-2-one or linalyl acetate + nerolidol. These VOC also caused alterations in the concentrations of substances such as alkaloids, phenols, amino acids and carbohydrates, in the roots of coffee plants. The findings suggest that these VOC may be explored as potential products for the control of M. exigua in coffee plants.

Resumo em Inglês:

Epicoccum sp. showed in vitro antagonism to the rice pathogens Magnaporthe oryzae, Rhizoctonia solani, Sarocladium oryzae, Monographella albescens and Cochliobolus miyabeanus in dual culture. The colony growth of the rice blast fungus, M. oryzae, was reduced by 42.50%. The lethal doses (LD50) determined based on probit-log dosage response curves at 3 and 6 hours after germination were 393.0 and 326.6 ppm, respectively. The crude extract (600 ppm) reduced appressorial formation by 95.68%. A greenhouse experiment comparing the relative efficiency of conidial suspension and crude extract of Epicoccum sp. in the suppression of leaf blast showed no statistical difference between both application methods. However, the crude extract of Epicoccum sp. (4000 ppm) 48 hours before the application of M. oryzae induced resistance and suppressed leaf blast by 97.6%. Scanning electron microscopy of rice leaves inoculated with crude extract of Epicoccum sp. and challenged with M. oryzae showed appressorial deformation on penetration phase. Peroxidase and β-1,3-glucanase activities increased in plants sprayed with crude extract of Epicoccum sp., 24 hours after the application of the challenger. PAL as well as chitinase activities increased 72 hours after challenge inoculation. Epicoccum sp. was shown to be a potential antagonist and inducer of resistance against M. oryzae.

Resumo em Inglês:

Pseudomonas putida P286 and Bacillus thuringiensis B157 controlled coffee rust under greenhouse and field conditions. Now we studied the mechanism(s) of antagonism of both bacteria to Hemileia vastatrix. Bacterial effects on urediniospore germination and disease severity were evaluated in experiments with six treatments: (i) growth broth, (ii) supernatant centrifugation, (iii) bacterial cell centrifugation and re-suspension, (iv) UV inactivation of the bacteria, (v) 523 medium, and (vi) saline solution. The treatments i to iii reduced both spore germination and disease severity. Each isolate was applied at different concentrations and time periods before inoculation of H. vastatrix. The efficiency in controlling rust was reduced at the lowest concentrations and at the largest intervals between applications. In spatial separation experiments, both bacteria did not induce systemic protection, whereas protected locally the coffee plants against H. vastatrix. Therefore, the mechanism of both isolates against H. vastatrix is attributed to the production of antifungal compound (s).

Resumo em Inglês:

Calonectria pteridis is one of the most important causal agents of Calonectria leaf blight (CLB) of Eucalyptus spp. in Brazil, which is a limiting factor for growth of Eucalyptus plantations. In this study we developed standard procedures for in vitro mass spore production and inoculation of C. pteridis for screening plant species and clones for resistance to CLB. The isolates used in this study were identified using similarity in DNA sequence to reference strains. Among six media tested, glucose asparagine agar induced the highest sporulation production and a significantly enhanced sporulation was found by scraping the aerial mycelium and temporarily submersing the cultures in tap water, followed by drying and additional incubation of the culture. We also demonstrated that the severity of CLB on excised leaves of two Eucalyptus spp. clones increased significantly when the inoculated leaves were incubated in the dark. The optimal temperature for infection was 26ºC when plants were incubated for 48 hours post-inoculation in a mist chamber and then maintained in a greenhouse (25ºC±5ºC) for 50 days. This study identifies environmental conditions to improve spore production and inoculation procedures of C. pteridis for selection of resistant Eucalyptus spp.

Resumo em Inglês:

The effectiveness of composted sewage sludge incorporated into Pinus bark-based substrate with or without biofertilizer, fish hydrolyzate, chitosan and Trichoderma asperellum was evaluated for the control of Fusarium wilt in chrysanthemum. The substrate was obtained from pots containing chrysanthemum plants killed by the pathogen. Half of the substrate was sterilized prior to the incorporation of sewage sludge (0, 10%, 20% and 30% v/v). These substrates were or were not supplemented with the following: biofertilizer, fish hydrolyzate and Trichoderma. The mixtures were transferred to pots, and the chrysanthemum was transplanted. For all treatments, half of the plants were sprayed weekly with chitosan. Assessment of severity was performed on the 8th, 12th, 15th and 20th week after transplanting. In the 12th week, microbiological and chemical analysis of the substrate was performed. The incorporation of composted sewage sludge into the Pinus bark-based substrate significantly reduced Fusarium wilt, which was progressively decreased as the concentration of sewage sludge increased. The addition of biofertilizer, fish hydrolyzate, chitosan and Trichoderma had no effect on the disease. The microbial community was greater in non-disinfested substrates. The results indicate that suppressiveness is related to the interaction of chemical and microbiological factors.

Resumo em Português:

A busca por alternativas ao uso intensivo de agrotóxicos no controle de doenças tem recebido grande atenção da pesquisa agrícola. Rizobactérias têm reconhecida capacidade de reduzir doenças em diversas culturas e promover de crescimento de plantas. O objetivo deste trabalho foi avaliar a eficácia de seis isolados de rizobactérias, pré-selecionadas, no controle de Ralstonia solanacearum e Fusarium oxysporum f. sp. lycopersici (FOL), em casa de vegetação e relacionar este comportamento a produção de compostos "in vitro". Foi avaliada a capacidade de estas rizobactérias produzirem quitinases, amilases, lipases, compostos antibióticos e de solubilizar fosfato. A microbiolização das sementes com a rizobactéria DFs1421 (Pseudomonas sp.) reduziu os valores de AACPD de murcha bacteriana em ambos os ensaios (36,6 e 91,7% no primeiro e segundo ensaios respectivamente). Este controle pode ser associado à produção de compostos responsáveis pela antibiose observada "in vitro". Isolados de Streptomyces (DFs1296 e DFs1315), bem como de Bacillus (DFs1414) e o indutor químico ASM reduziram significativamente a murcha de fusário, variando de 22,5 a 76%. O controle observado por parte das rizobactérias pode ser atribuído à atividade quitinolítica e/ou antibiótica por compostos voláteis.

Resumo em Inglês:

Replacing the intensive use of pesticides for alternative methods in disease control has been an important aim for agricultural research. Rhizobacteria are known to be capable of reducing diseases levels in many crops and also of promoting plant growth. The objective of this work was to evaluate the efficacy of six pre-selected rhizobacteria isolates in controlling Ralstonia solanacearum and Fusarium oxysporum f. sp. lycopersici (FOL) under controlled conditions in a greenhouse, and to link such capacity to the "in vitro" production of selected biologically active compounds. The ability of these rhizobacteria isolates to produce chitinases, amylases, lipases, antibiotic compounds was investigated. Additionally, their ability in solubilizing phosphate was also checked. Microbiolization of seeds with one rhizobacterium DFs1421 (Pseudomonas sp.) reduced the tomato wilt AUDPC in both assays (36.6 and 91.7% in the first and second assays respectively). Such efficacy in wilt control is likely to be linked with the production of antibiotics as observed "in vitro". Streptomyces (DFs1296 and DFs1315) and Bacillus (DFs1414), and the chemical inducer (ASM) reduced significantly fusarium wilt ranging 22.5 to 76%. This may be owing to the observed chitinolytic activity and / or antibiosis in the presence of volatile compounds.

Resumo em Inglês:

The incidence of target spot disease on soybean has increased in recent years in Brazil even with intensive use of fungicides, and fungal resistance has been reported in recent studies. The objective of this study was to determine the fungicide sensitivity to carbendazim and prothioconazole in a sample of 24 isolates of Corynespora cassiicola from soybean collected from 1996 to 2011 in the states of Paraná, Mato Grosso and São Paulo ( Brazil) and Corpus Christi (Paraguay). The 50% effective concentration (EC50) values were estimated by the relative mycelium growth reduction on fungicide-amended medium with the doses of 0, 0.5, 1, 10, 100 and 1000 µg of active ingredient/ mL. For carbendazim, four highly resistant isolates (EC50>50 µg/mL) were observed from samples collected from Mato Grosso in 2008 and from Paraná and Mato Grosso in 2011. The EC50 values for prothioconazole ranged from 0.47 µg/mL to 26.44 µg/mL (mean: 5.02 µg/ ml). The results reinforce the occurrence of C. cassiicola resistance to benzimidazole in Paraná and Mato Grosso states.

Resumo em Inglês:

This study aimed to evaluate the effect of silicon (Si) on the resistance of tomato plants (cv. Santa Clara) to bacterial speck, caused by Pseudomonas syringae pv. tomato (Pst). Tomatoes were grown in soil without calcium silicate (control), in soil without calcium silicate and sprayed with Supa Sílica® (2 mL/L) (SS) and in soil with calcium silicate (0.16 g/kg of soil) (CS). The effect of SS on the growth of Pst was evaluated in vitro. There was no significant difference among the treatments for foliar Si concentration and incubation period. No significant differences were observed between the control and CS for the number of lesions per plant (NLP) and bacterial speck severity estimated by the software QUANT. The NLP was significantly reduced with SS spray. There was a negative linear response of in vitro Pst growth to the SS rates. Peroxidase, polyphenoloxidase and glucanase activities were significantly higher for plants sprayed with SS and grown in soil with CS compared to the control treatment. Phenylalanine ammonia-lyase and lypoxygenase activities were significantly higher for plants grown in soil with CS compared to the control. The concentration of malondialdehyde was significantly higher for plants sprayed with SS compared to the control at 0 and 7 dai. The results of this study indicate that the symptoms of bacterial speck are reduced when plants are sprayed with SS, which can be linked to the direct effect of this product against Pst rather than the potentation of host defense responses.

Resumo em Inglês:

Sugarcane leaf rust symptoms were observed on seven month-old plants in March 2012 at Santa Teresa Farm, north coast of Pernambuco, Brazil. Plants were identified as a genotype coded as RBUFRPE0032 developed by the Sugarcane Breeding Program of Universidade Federal Rural de Pernambuco (UFRPE/EECAC). Evaluations under field conditions showed characteristic leaf rust symptoms and high severity. Analysis of symptomatic leaves under the optical microscope at the Plant Pathology Laboratory of UFRPE/EECAC confirmed the presence of fungal urediniospores showing specific characteristics of the fungus. Molecular evaluation by real-time PCR yielded positive results for Puccinia kuenhii. This is the first report of sugarcane leaf rust in Pernambuco. Although the disease has been reported in other Brazilian states, producers and researchers are worried since the behavior of promising commercial varieties and clones from breeding programs directed at the soil and climatic conditions of the state is unknown. The Ministry of Agriculture in Pernambuco was officially informed for notification purposes.

Resumo em Inglês:

In the present work, the susceptibility of wild and domesticated plants of Momordica charantia to viruses from the genus Potyvirus that cause diseases in papaya (Carica papaya) and cucurbit crops was evaluated. The plants were subjected to experimental and natural infection with Papaya ringspot virus types P and W (PRSV-P and PRSV-W) and Zucchini yellow mosaic virus (ZYMV). None of the potyviruses infected the wild type of M. charantia through mechanical or aphid inoculation or under field exposition, whereas the domesticated type was only infected by isolates of ZYMV. In addition, both wild and domesticated types of M. charantia were not infected in natural conditions by an isolate of Zucchini lethal chlorosis virus, genus Tospovirus, transmitted by Frankliniella zucchini. These data clearly indicated that this wild type of M. charantia does not seem to have a role in the epidemiology of the diseases caused by these three potyviruses in Brazil.

Resumo em Inglês:

Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) causes bacterial wilt on beans (Phaseolus vulgaris) and bacterial tan spot on soybeans (Glycine max). Cff was detected on beans in Brazil in 1995. Plants of commercial and experimental fields of soybean with typical symptoms of the disease were collected in the State of Paraná, Brazil, during the 2011/2012 growing season. The causal agent was identified as Cff by isolation from symptomatic leaves on CNS semi-selective medium, artificial inoculation test and re-isolation in soybean and bean, Gram staining test, solubility in KOH, and by PCR. This is the first report of Cff on soybean in Brazil.