Influence of substrates, light, filter paper and pH on the sporulation of Cercospora sojina

Fungi require special substrates for their isolation, vegetative growth and sporulation. In experiments conducted in the laboratory, the influence of substrates, light, filter paper and pH on the sporulation of Cercospora sojina conidia, the causal agent of soybean frogeye leaf spot, was assessed. The media potato sucrose agar, V-8 agar, tomato extract agar, soybean leaf extract agar, soybean seed extract agar, soybean meal agar, soybean flour agar and wheat flour agar were tested, added on the surface, with and without filter paper and under two light regimes, with 12 h light at 25°± 2°C and in the dark. A triple factorial 8x2x2 (substrates x light/dark x with/without filter paper) design with four replicates was used. V-8 agar medium was employed and the pH was adjusted with HCl 0.1N or NaOH 0.1N before autoclaving to the values: 3, 4, 5, 6, 7 and 8, and the pH of V-8 agar medium is 6.7. The evaluation was done on the seventh day of incubation. Data underwent regression analysis. Sporulation was maximized on the agar media V-8, seed extract, oat flour, tomato extract, and potato sucrose in the presence of filter paper and 12h light. On V-8 medium, maximal sporulation was obtained with pH 6.7.Os fungos requerem substratos especiais para seu isolamento, crescimento vegetativo e esporulação. Em experimentos conduzidos no laboratório foram avaliadas a influência de substratos, luz, papel de filtro e pH na esporulação de conídios de Cercospora sojina agente causal da mancha foliar olho-de-rã da soja. Foram testados os meios ágar batata sacarose, ágar V-8, ágar extrato de tomate, ágar extrato de folha de soja, ágar grãos de soja, ágar farelo de soja, ágar farinha soja e ágar farinha de aveia, acrescidos na superfície com e sem papel de filtro e submetidos a dois regimes luminosos, com luz de 12 h a 25°± 2°C e sem luz. O delineamento experimental usado foi fatorial triplo 8x2x2 (substratos x luz/escuro x com/sem papel de filtro), com quatro repetições distribuídas ao acaso. Usou-se o meio ágar V-8 ajustando o pH com HCl 0.1 N ou NaOH 0.1 N antes da autoclavagem nos valores: 3; 4; 5; 6; 7 e 8, sendo o pH do meio ágar V-8 de 6.7. A avaliação foi realizada aos sete dias de incubação. Os dados foram submetidos à análise da regressão. A esporulação foi maximizada nos meios V-8, ágar extrato de semente, farinha de aveia, extrato de tomate e batata sacarose ágar na presença de papel de filtro e fotoperíodo de 12 h. No meio V-8 a máxima esporulação foi obtida com o pH 6.7.EEA Sáenz PeñaFil: Gomez, Diana Erica. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Sáenz Peña; ArgentinaFil: Reis, Erlei Melo. Universidad de Passo Fundo. Facultade de Agronomía y Medicina Veterinaria. Departamento de Fitosanidad; Brasi

Semi-selective culture medium for Exserohilum turcicum isolation from corn seeds

Northern corn leaf blight, caused by Exserohilum turcicum (Et), is a disease of widespread occurrence in regions where corn, sweetcorn and popcorn are grown. This disease has great potential to cause damage and has been studied for years, but the association of its causal agent with seeds remains unconfirmed. Thus, the availability of a sensitive method to detect and quantify the inoculum in seeds, even at low incidence, is essential. The aim of this study was to develop a method to detect and quantify the presence of the fungus infecting and infesting corn and popcorn seeds. Artificially and naturally infected seeds were employed to develop the medium. The semi-selective medium was composed of carbendazim (active ingredient) (60 mg/L), captan (30 mg/L), streptomycin sulfate (500 mg/L) and neomycin sulfate (600 mg/L) aggregated to the medium lactose casein hydrolysate agar medium. By using this, Et was detected in naturally infected corn seeds, showing 0.124% incidence, in four out of ten analyzed samples. In addition, 1.04 conidia were detected per infested seed. By means of isolation, pathogenicity test, morphological characterization and comparison with descriptions of the species in the literature, the fungus isolated from the seeds was confirmed to be Et. Both infection and infestation were considered low; thus, for studies of Et detection in corn seeds, the use of semi-selective medium and more than 1,200 seeds/sample is suggested.Fil: De Rossi, Roberto Luis. Universidad Católica de Córdoba. Facultad de Ciencias Agropecuarias; Argentin

Adição de mancozebe às misturas de fungicidas IDMs + IQes e IQes + ISDHs no controle das manchas foliares do trigo

Reis, Erlei Melo. Universidad de Buenos Aires. Facultad de Agronomía. Buenos Aires, Argentina.Zanatta, Mateus. Agroservice - Pesquisa e consultoria agrícola. Passo Fundo - RS, Brasil.Forcelini, Carlos Alberto. Universidade de Passo Fundo. Faculdade de Agronomia. Passo Fundo - RS, Brasil.23-27Wheat leaf blights caused by Drechslera siccans, D. tritici-repentis, especially D. tritici-repentis, are difficult to be controlled by site-specific fungicide mixtures. Due to development of resistance, the use of double site-specific mixtures has shown control inferior to 50%. In an experiment conducted in the field with the wheat cultivar Jadeite 11, in 3 x 6 m plots and four replicates, the effect of a muli-site fungicide added to fungicide mixtures on the control of leaf blights was evaluated. The effect of the following mixtures was evaluated: picoxystrobin + cyproconazole, kresoxim-methyl + epoxiconazole, azoxystrobin + cyproconazole, pyraclostrobin + epoxiconazole, pyraclostrobin + fluxapyroxad, trifloxystrobin + prothioconazole and zoxystrobin + propiconazole, added of five mancozeb levels, 0; 1.5; 2.0; 2.5 and 3.0 kg/ha. The first application occurred after 30% Reis, E. M.; Zanatta, M.; Forcelini, C.A. Addition of mancozeb to the fungicide mixtures DMI + QoI and SDHI + QoI on the control of wheat leaf blights. Summa Phytopathologica, v.45, n.1, p.23-27, 2019. leaf incidence, and the remaining two occurred at 15 and 18-day intervals. The fungicides were applied with a backpack sprayer pressurized by CO2, delivering 180 L/ha. Leaf blights severity was quantified, control was calculated, the percentage of chlorophyll in flag leaves was determined, and grain yield was assessed. The mean control of leaf blights by the mixtures without addition of the multi-site fungicide was 44%. The disease severity reduced as a function of the addition of mancozeb levels for all treatments. Control superior to 80% was obtained with the mixtures resoxim methyl + epoxiconazole and pyraclostrobin + epoxiconazole, both added at least 2.0 kg/ha mancozeb. There was a positive reflex on the increase in wheat grain yield as a function of control, varying from 3005 kg/ha for the best treatment to 2026 kg/ha for control

Comparação da eficácia de fungicidas IQes, isolados ou em mistura com triazóis, no controle da ferrugem asiática da soja, safra 2016/17

Reis, Erlei Melo. Universidad de Buenos Aires. Facultad de Agronomía. Buenos Aires, Argentina.Carregal, Luis Henrique. Agrocarrega. Rio Verde, Goiás - GO, Brasil.Zanatta, Mateus. Agroservice. Passo Fundo, RS, Brasil.28-32Evolution has been reported for the reduction in Phakopsora pachyrhizi sensitivity to the mixtures of the three site-specific mechanisms of action (DMIs, QoIs and SDHIs) used in its control. The aim of this study was to quantify the current contribution of QoIs, alone or in mixture with triazoles, in the control of Asian soybean rust. In an experiment carried out in the field, the efficacy of quinone outside inhibitors (QoIs), or strobilurins, was compared for Asian soybean rust control. The isolated effects of four doses of azoxystrobin, picoxystrobin, pyraclostrobin and trifloxystrobin were evaluated, as well as of four applications during the crop cycle. Control by commercial mixtures of these QoIs with triazoles was also compared. Severity was evaluated in four phenological stages, and control was calculated based on final severity data, area under rust progress curve, defoliation, one-thousand-grain mass, grain yield and damage caused by the disease. The lowest mean of rust control efficacy resulted from applications of azoxystrobin (15.8 and 11.19%) and pyraclostrobin (15.4 and 16.76%) and the highest mean was found for picoxystrobin (54.1 and 54.35 %) and trifloxystrobin (69.7 and 64.46%), calculated based on final severity and AUDPC, respectively. Such efficacy is not enough to cover the fungicide application cost, although there was a positive effect of treatments on disease control and grain yield

Fungicide baseline for mycelial sensitivity of Exserohilum turcicum, causal agent of northern corn leaf blight

Northern corn leaf blight, caused by Exserohilum turcicum (Et), is one of the major corn diseases which can reduce grain yield and quality. The aim of this study was to determine the mycelial sensitivity of ten Et isolates, five from Argentina and five from Brazil, to six fungicides (carbendazim, captan, fludioxinil, metalaxyl, iprodione and thiram) used in seed treatment. The inhibitory concentration (IC50) was determined by using seven concentrations of the fungicides supplemented to the agar medium. The mycelial colony diameter was measured with a digital caliper. Experimental design was completely randomized with four replicates. Data on the percent mycelial growth inhibition were analyzed by logarithmic regression and the IC50 was calculated. The fungicide iprodione was the most potent, with IC50 < 0.01 mg/L, followed by fludioxonil, IC50 0.31 mg/L, and thiram, 1.37 mg/L. Carbendazim, metalaxyl and captan were classified as non-fungitoxic, showing IC50 > 50 mg/L for all isolates. Although iprodione is the most potent fungicide, it is not used for corn seed treatment. The IC50s obtained in this study can be used as baseline for future monitoring studies of Et sensitivity to fungicides.Fil: De Rossi, Roberto Luis. Universidad Católica de Córdoba. Facultad de Ciencias Agropecuarias; Argentin

Malezas hospedantes de hongos necrotróficos causantes de enfermedades en trigo y cebada cervecera en la Región Pampeana

p.105-110Con el objetivo de determinar la im portancia de hospedantes secundarios en la supervivencia de hongos patógenos de trigo y cebada, se realizó una recolección de malezas en campos de producción agrícolas a partir de las cuales, hongos patógenos necrotróficos fueron aislados de síntomas de raíces, hojas y semillas. El patógeno más frecuentem ente aislado fue Bipolaris sorokiniana. Este hongo fue aislado de raíces de raygrass (Lolium multiflorum); cebadilla (Bromus unioloides), festuca (Festuca arundinacea), de hojas de avena (Avena sativa), cola de zorro (Hordewn Leporinum), malva (Anoda cristata), Chenopodium album (quinoa), de festuca y cebadilla. Asimismo B. sorokiniana fue observado en semillas de raygrass y de avena. Gaeummanomyces graminis var. tritici fue aislado de raíces de raygrass, y Fusarium graminearum de tallos de quinoa (Chenopodium quinoa), y de festuca como así también de raíces de sorgo de alepo (Sorghum halepense) y de gramón (Cynodon dactylon), y en semillas de Spartina argentiniensis. De manchas foliares en raygrass se aisló Rhynchosporium secalis. Estos hospedantes podrían constituir una importante fuente de inoculo y por lo tanto la rotación de cultivos debería ser complementada con la reducción poblacional de estas plantas. Se cita por primera vez, a malezas invasoras como huéspedes secundarios de patógenos necrotróficos de trigo y cebada cervecera en Argentina

Pathogenicity of Beauveria bassiana to soybean pest insects

Em ensaios de laboratório realizados no CNPT - Passo Fundo, RS, em 1976, demonstrou-se a patogenicidade de Beauveria bassiana (Balsamo) Vuillemim sobre as espécies Nezara viridula (L., 1758) e Diabrotica speciosa (Germar 1824), pragas da soja, Glycine max, L. (Merrill). Objetivando-se a obtenção de inóculo para trabalhos de campo, estudaram-se fatores que influem na esporulação do fungo. Foi demonstrado que o meio de cultura de semolina-ágar, com pH 6,0 e sob fotoperíodo de doze horas de luz x doze horas de escuro, promoveu a máxima produção de inóculo.The pathogenicity of Beauveria bassiana (Balsamo) Vuillemim on the soybean Glycine max, L. (Merrill) pest species Nezara viridula (L., 1758) and Diabrotica speciosa (Germar 1824) has been demonstrated in trials conducted in 1976 at Passo Fundo, Rio Grande do Sul State, Brazil under laboratory conditions. Aiming at to obtain the inoculum for field work, the factors influencing fungus esporulation have been studied. It has been demonstrated that culture medium of "Semolina-Ágar", with pH 6.0 and exposed to a photo-period of twelve hours under light and twelve hours in dark, gives the maximum production of inoculum

Rotação de culturas. XVIII Influência de sistemas de rotação de culturas no rendimento e na intensidade de doenças do sistema radicular do trigo.

Between 1979 and 1987, at the National Wheat Research Center-CNPT, in Passo Fundo, RS, Brazil, an experiment including two systems of rotation for wheat (Triticum aestivum L.) was carried out. Effetcs of crop rotation on wheat yield, root diseases severity, yield components, and on some agronomic characteristics of wheat plante were assessed. Systems of rotation were: 1) wheat, oats and flax, or; 2) wheat, lupins and rapeseed. A randomized block design with four replications was used and plots area was 120 m2. Wheat showed higher yield and plant hight when grown alter lupins and rapeseed than alter oats and flax. In both systems wheat presented stability of grain yield. It was concluded that there was no effect of the rotation systems on root rot diseases.No período de 1979 a 1987, foi avaliado, no Centro Nacional de Pesquisa de Trigo-CNPT Passo Fundo, RS, o efeito de dois sistemas de rotação de culturas no rendimento de grãos, na intensidade de doenças do sistema radicular, nos componentes do rendimento e em algumas características agronômicas do trigo (Triticum aestivum L.). Os tratamentos constaram de dois sistemas de rotação para trigo; este cereal retornou à mesma área a cada três anos, sendo intercalado, num sistema, com aveia e linho, e no outro, com tremoço e colza. O ensaio foi delineado em blocos ao acaso com quatro repetições e a área útil da parcela foi de 120 m2. O trigo apresentou rendimento de grãos e estatura de plantas mais elevados quando antecedido por tremoço e por colza, do que por aveia e por linho. Em todos os anos, com exceção de 1983, o trigo mostrou, nos dois sistemas propostos, estabilidade de rendimento de grãos. Constatou-se que não houve efeito dos sistemas de cultivo sobre a intensidade das doenças do sistema radicular

Crop rotation. VIII. Effect of crop systems on wheat yield

No período de 1980 a 1985, foi avaliado, no Centro Nacional de Pesquisa de Trigo (CNPT), o efeito de alguns sistemas de rotação de culturas sobre o rendimento de grãos de trigo. O trigo foi semeado em monocultura ou retornou à mesma área a cada um, dois ou três invernos. Os tratamentos foram arranjados em blocos ao acaso, com quatro repetições e a área útil das parcelas foi de 120,0 m2. As culturas de inverno e o milho foram estabelecidos com o sistema convencional de preparo do solo e a soja em plantio direto. O trigo, nos últimos três anos, foi cultivado após as seguintes culturas de inverno: a) trigo, trigo, trigo; b) colza, linho, tremoço; c) colza, cevada, tremoço; d) trevo, trevo ou trevo, ervilhaca. O rendimento de grãos de trigo na rotação de inverno (colza, linho, tremoço; colza, cevada, tremoço; trevo, trevo ou trevo, ervilhaca) foi, na maioria dos anos, superior ao rendimento do trigo em monocultura. O grau de intensidade de doenças radiculares foi maior quando se cultivou trigo todos os anos do que nos demais tratamentos de rotação de culturas. O peso de 1.000 grãos foi o componente que melhor se correlacionou com o rendimento de grãos. A cevada teve um rendimento de grãos superior ao trigo nas mesmas condições.  From 1980 up to 1985, at the National Wheat Research Center (CNPT), the effect of some crop systems on wheat yield was assessed. A crop rotation schedule was followed in such a way that wheat was seeded in every year or at intervals of one, two, and three winters. Treatments were arranged in randomized complete block design with four replications. Plot areas was of 120.0 m2. The seedbed for us the winter crops and corn was the traditional and soybeans direct drilled. Wheat was cropped every year and in rotations with a) rapessed, flax and white lupin; b) with rapessed, barley and white lupin; c) with subterranean clover cropped for two years and vetch. Wheat yield was higher in rotation than under cropped every year. Root disease rating showed higher values for monoculture than for the other systems of rotation. One thousand kernels weight was the yield component that presented better correlation to yield. The barley yield was higher than wheat.