Marcos Gomes da Cunha

Reação de cultivares de soja à Corynespora cassiicola

O fungo Corynespora cassiicola, agente causal da mancha-alvo em soja, tem ocorrido com frequencia na regiao Centro-Oeste do Brasil e pode, sob condicoes de alta temperatura e alta umidade, causar serios danos a cultura. O uso de cultivares resistentes ao patogeno e recomendado, porem sao poucas as disponiveis no mercado. Este trabalho foi realizado visando avaliar a reacao de doze cultivares comerciais de soja inoculados com C. cassiicola, em casa de vegetacao e no campo. A severidade foi avaliada utilizando escala diagramatica de severidade da mancha-alvo. As cultivares menos suscetiveis ao patogeno na casa de vegetacao foram BRSGO 7960 e BRS Sambaiba e as mais suscetiveis foram BMX Potencia RR e M-SOY 7908 RR. No campo, as cultivares menos suscetiveis foram M-SOY 8866, M-SOY 7908 RR e BMX Potencia RR e as mais suscetiveis foram BRSGO 8360 e BRS Tracaja.

Reaction of hybrids, inhibition in vitro and target spot control in cucumber

The fungus Corynespora cassiicola is the causal agent of target spot in cucumber. Under favorable climatic conditions it can cause serious damage in this horticultural crop. In Brazil, there exists not enough knowledge to determine efficient control measures to the disease. This investigation was carried out to evaluate: a) the reactions of nine cucumber hybrids to C. cassiicola; b) the sensibility of six isolates of C. cassiicola to fungicides in vitro (captan, chlorothalonil, mancozeb, azoxystrobin, difenoconazole, carbendazin, tebuconazole and thiophanate-methyl), used in concentrations of 0, 1, 10, 100 and 1,000 µg mL -1 of active ingredient and c) protective and curative chemical treatments with the same fungicides used in vitro in cucumber plants inoculated with C. cassiicola. The cucumber hybrids were evaluated using the scale of notes and diagrammatic of target spot severity. The more resistant hybrids to the pathogen were Taisho, Nikkey, Yoshinari and Safira. The difenoconazole fungicide caused the most mycelial growth inhibition (MGI) and showed the lowest ED 50 . Thiophanate-methyl was the worst fungicide, it did not inhibit the mycelial growth of the fungus. Azoxystrobin was the most efficient in controlling the disease, although it has to be registered in Ministry of Agriculture, Livestock and Food Supply in Brazil before its recommendation.

Incidence of Sclerotinia sclerotiorum and the physical and physiological quality of soybean seeds based on processing stages

Soybean (Glycine max L. Merrill) is infected by a large number of fungal pathogens, among them white mold agent [Sclerotinia sclerotiorum (Lib) de Bary]. The objective of this study was to verify the effect of the seed-processing stages on the physical and physiological qualities and on the incidence of S. sclerotiorum in soybean seeds. In this study, seeds from eight cultivars coming from production fields naturally infested in the counties of the State of Goias, Brazil, from two harvests (2009/2010 and 2010/2011), were used. Samples were collected in the processing stages: hopper, pre-cleaning, discard one (from pre-cleaning), cleaning, sieve classifiers, spiral, gravity table, and discard two (after cleaning until processing ending). The following parameters were evaluated: seed- moisture content, physical purity, germination and tetrazolium. Additional tests and the detection of S. sclerotiorum in paper roll and the neon method were performed. The processing of soybean seeds improves the physical and physiological quality of the seed lots, in addition to eliminating sclerotia. The stages of pre-cleaning and cleaning significantly reduce sclerotia in seed lot. The amount of sclerotia in the sample is not necessarily correlated with the incidence of S. sclerotiorum in mycelial form.

Detection of Pantoea agglomerans in Germplasm Rice Accessions (Oryza sativa) in Brazil

The cultivated area devoted to rice crops (Oryza sativa) in Brazil has expanded in recent years, along with improvements in yield. This has prompted the continuous exchange of material from Active Germplasm Banks between government breeding programs. When placed in a greenhouse for multiplication purposes, rice accessions resulting from exchanges between ARS/USDA (Agricultural Research Service/United States Department of Agriculture) showed little or no germination. The accessions were sent to the tissue culture laboratory of BAG-CNPAF (Embrapa National Rice and Bean Research Center) with a view to recovering embryos by aseptically removing the seed coat of ten seeds from each accession. Bacterial colony growth concomitant to germination inhibition was observed in some accessions, from which four bacterial isolates were obtained. The isolates and their respective associated rice accessions are: Bac 1887 from accession Chikanari 2 (CIor 12454), Bac 2821 from Fujisaka 2 (PI 184496), Bac 2926 from Ehime Suit...

In vitro sensitivity of Corynespora cassiicola isolated from soybean to fungicides and field chemical control of target spot.

Soybean target spot (Corynespora cassiicola) has become an important disease in most soybean growing regions in Brazil. The sensitivity of 34 isolates of C. cassiicola to 11 fungicides was evaluated based on mycelial growth inhibition (boscalid, carbendazim, cyproconazole, fluopyram, fluxapyroxad, prothioconazole and thiophanate-methyl) or spore germination inhibition (azoxystrobin, picoxystrobin, pyraclostrobin and trifloxystrobin). In addition, the efficacy of five fungicides to control target spot was tested in four field trials carried out during three crop seasons: 2011/2012, 2012/2013 and 2013/2014. Fungal isolates were collected from soybean plants in several soybean growing areas in Brazil. The effective concentration of each fungicide to inhibit fungal growth or spore germination by 50% (EC 50 ) was calculated for all isolates. Fluxapyroxad and prothioconazole provided the greatest mycelial Teramoto, A.; Meyer, M.C.; Suassuna, N.D.; Cunha, M.G. In vitro sensitivity of Corynespora cassiicola isolated from soybean to fungicides and field chemical control of target spot. Summa Phytopathologica, v.43, n.4, p.281-289, 2017.

Caracterização fisiológica de isolados de Corynespora cassiicola

Corynespora cassiicola is the causal agent of target spot on several crops of economic importance. Since the availability of standardized protocols for inoculum production makes the conduction of patogenicity tests easier, the objectives of this work were to evaluate the mycelial growth under different temperatures, to evaluate the mycelial growth and spore production under different photoperiods for isolates obtained from different hosts, to evaluate the effect of continuous humidity on spore germination, and the pathogenicity of seven isolates of C. cassiicola on several hosts. Temperatures between 23,3 and 29,5oC allowed the best growth of the isolates. The growth of eight isolates did not respond to the photoperiods used whereas six isolates were sensitive to the dark. The best sporulation for the majority of isolates was under continuous light. Five to twenty hours of continuous humidity were enough for 85% of the spores to germinate. As for pathogenicity, cotton, melon and cucumber were the most susceptible hosts, while tomato, coffee and Antilles cherry were the least susceptible. For massal production of C. cassiicola inoculum, a temperature of 25oC under continual light is recommended.

Plant-associated bacteria mitigate drought stress in soybean

Agriculture accounts for ~ 70% of all water use and the world population is increasing annually; soon more people will need to be fed, while also using less water. The use of plant-associated bacteria (PAB) is an eco-friendly alternative that can increase crop water use efficiency. This work aimed to study the effect of some PAB on increasing soybean tolerance to drought stress, the mechanisms of the drought tolerance process, and the effect of the PAB on promoting plant growth and on the biocontrol of Sclerotinia sclerotiorum. PAB were isolated from soybean rhizosphere and S. sclerotiorum sclerotia. The strains identified as UFGS1 (Bacillus subtilis), UFGS2 (Bacillus thuringiensis), UFGRB2 and UFGRB3 (Bacillus cereus) were selected on their ability to grow in media with reduced water activity. Soybean plants were inoculated with the PAB and evaluated for growth promotion, physiological and molecular parameters, after drought stress. Under drought stress, UFGS2 and UFGRB2 sustained potential quantum efficiency of PSII (Fv/Fm), while a decrease was found in the control plants. Moreover, UFGS2 and UFGRB3 maintained the photosynthetic rates in non-stressed conditions compared to the control. UFGS2-treated plants showed a higher stomatal conductance and higher transpiration than the control, after drought stress. Some PAB-treated plants also had other beneficial phenotypes, such as increases in fresh and dried biomass relative to the control. Differential gene expression analysis of genes involved in plant stress pathways shows changes in expression in PAB-treated plants. Results from this study suggest that PAB can mitigate drought stress in soybean and may improve water efficiency under certain conditions.

MOLECULAR DIAGNOSIS OF Guignardia citricarpa IN ASYMPTOMATIC SWEET ORANGE TISSUE

Citrus black spot, a fungal disease caused by the quarantine fungus Guignardia citricarpa, restricts the exportation of fresh fruit to countries in the European Union. The occurrence of latent infections and the time required for diagnosis using conventional methods have brought about the need to validate fast, efficient and reproducible molecular techniques to detect the pathogen in asymptomatic tissue. As such, this study aims to detect G. citricarpa in the symptomatic fruit and asymptomatic leaf tissue of sweet oranges by conventional and real-time polymerase chain reaction (PCR). Specificity and limit of detection (LOD) were assessed in tissue samples of fruit lesions and asymptomatic leaves. Low concentrations of the fungus were found in asymptomatic leaves. Under these conditions, real-time PCR proved to be viable, reproducible and highly sensitive to detection of the pathogen.

Detecção simultânea de fatores de resistência à murcha de fusário do tomateiro por meio de PCR multiplex

The objective of this work was to develop and validate a protocol for simultaneous detection by multiplex polymerase chain reaction (multiplex PCR) of tomato ( Solanum lycopersicum ) genomic regions associated with factors of resistance to three physiological races of Fusarium oxysporum f. sp. lycopersici (FOL). The employed primer pairs were SSR‑67 (specific to the I‑1 gene), TFusrr (specific to the I‑2 gene), and SSRD (specific to the I‑3 gene). Genotyping results with molecular markers were compared with the phenotyping ones of a tomato germplasm collection, in bioassays of isolate inoculation of the three FOL races in seedlings by root dipping. The resistance or susceptibility was confirmed by PCR, through the visualization of specific amplicons corresponding to the target regions linked to the factors of resistance to distinct FOL races. The elaborated protocol for the joint use of the molecular markers, by multiplex PCR, allows of the selection of tomato accessions that are resistant to the races 1, 2, and 3 of F. oxysporum f. sp. lycopersici in a similar way to that done with each one separately. PCR multiplex is a viable tool to monitor the incorporation of these resistance factors into tomato inbred lines.

Manejo de ferrugem da soja com fungicidas em tratamento de sementes e aplicação foliar

Soybean is an important crop in the economical agriculture of Brazil and it has productive potential compromised by a variety of diseases affecting the crop ...