Black root rot, caused by Macrophomina phaseolina (Tass.) Goid., is the most common root disease in soybean fields. This study aimed to determine the in vitro mycelial sensitivity, measured by the IC50 (concentration to inhibit 50% of the fungus mycelial growth) of a M. phaseolina isolate obtained from soybean, to different fungicides (thiram, iprodione, carbendazim, pyraclostrobin, fluquinconazol, tolyfluanid, metalaxyl and penflufen + trifloxystrobin), at six concentrations (0.01 mg L-1, 0.10 mg L-1, 1.00 mg L-1, 10.00 mg L-1, 20.00 mg L-1 and 40.00 mg L-1 of the active ingredient). The 0.00 mg L-1 concentration represented the control, without fungicide addition. The mycelial growth evaluation was performed with the aid of a digital pachymeter, by measuring the colonies diameter, when the fungus growth in the control treatment reached the Petri dish edge. The experimental design was completely randomized, with four replications. Concerning the fungitoxicity of active ingredients, a variation from non-toxic to highly fungitoxic was observed to the M. phaseolina isolate, with IC50 values ranging from 0.23 mg L-1 to > 40.00 mg L-1, being carbendazim the most efficient one (IC50 = 0.23 mg L-1). The fungus showed insensitivity to the active ingredients of fluquinconazole, metalaxyl, thiram and tolyfluanid.
273Soybean target leaf spot, caused by the fungus Corynespora cassiicola, is controlled especially by leaf application of fungicides. In the last seasons, in the central-west region of Brazil, the disease chemical control efficiency has been low. This led to the hypothesis that the control failure could be due to the reduction or loss of the fungus sensitivity to fungicides. To clarify this fact, in vitro experiments were conducted to determine mycelial sensitivity of five C. cassiicola isolates to fungicides. Mycelial growth was assessed based on the growth of the mycelium on the culture medium, in Petri dishes. The medium potato-dextrose-agar was supplemented with the concentrations 0; 0.01; 0.1; 1; 10; 20 and 40 mg/L of the active ingredients carbendazim, cyproconazole, epoxiconazole, flutriafol and tebuconazole.Avozani, A.; Reis, E. M; Tonin, R. B. Sensitivity loss by Corynespora cassiicola, isolated from soybean, to the fungicide carbendazim. Summa Phytopathologica, v.40, n.2, p.273-276, 2014.Additional keywords: Chemical control, Glycine max, target leaf spot, fungicide resistance. ABSTRACTThe experiment was conducted and repeated twice in a controlled environment, temperature of 25 ± 2ºC and photoperiod of 12 hours. Data on the percentage of mycelial inhibition were subjected to logarithmic regression analysis and the concentration that inhibits 50% of the mycelial growth (IC 50 ) was calculated. Loss of sensitivity to carbendazim was observed for three fungal isolates, IC 50 > 40 mg/L. Considering all five isolates, the IC 50 for tebuconazole ranged from 1.89 to 2.80 mg/L, for epoxiconazol from 2.25 to 2.91, for cyproconazole from 9.21 to 20.32 mg/L, and for flutriafol from 0.77 to 2.18 mg/L. In the absence of information on the reference IC 50 determined for wild isolates, the lowest values generated in our study can be used as standard to monitor the fungus sensitivity.
Wheat (Triticum aestivum L.) is an important food crop in Brazil, where the annual consumption is currently around 11 million tons, of which 6 million tons are produced and 5.6 million tons are imported (5). Wheat production under prevailing warm and wet weather conditions, as in Southern Brazil, is a difficult task (15).Fungal diseases cause considerable damage to wheat production, particularly those difficult to control, such as fusarium head blight (FHB), caused by Gibberella zeae (Schw.) Petch. (Anamorph Fusarium graminearum Schw.). FHB was first described in the United States, in 1891 (19), and in Brazil, in Veranópolis County, Rio Grande do Sul, in 1942, by Costa Netto (7). RESUMOPalavras-chave adicionais: Giberela, fungitoxicidade, CI 50 , Triticum aestivum, trigo.Os danos causados pela giberela em trigo, no Brasil, podem chegara a 39,8%. Ainda não estão disponíveis cultivares resistentes para o controle da doença; desse modo, à curto prazo, o controle da doenças é baseado no uso de fungicidas. O primeiro passo para melhorar a eficácia do controle é monitorar a sensibilidade do fungo aos fungicidas para obter o manejo mais eficiente da doença. Experimentos foram conduzidos in vivo para avaliar a concentração inibitória (CI 50 ) de fungicidas tanto para o crescimento miceliano como para a germinação de conídios de dez isolados de Fusarium graminearum. Os seguintes fungicidas inibidores da desmetilação (IDM) foram testados: metconazol, protioconazol e tebuconazol. Também, foram testados os fungicidas inibidores da quinona externa (IQe) estrobilurinas, piraclostrobina e trifloxistrobina, bem Avozani, A.; Reis, E. M.; Tonin R. B. Redução in vivo da sensibilidade de Fusarium graminearum a fungicidas triazóis e estrobilurinas. Summa Phytopathologica, v.40, n.4, p.358-364, 2014. como suas misturas contendo metconazol + piraclostrobina, protioconazol + trifloxistrobina, e tebuconazol + trifloxistrobina. A média geral da CI 50 para o crescimento miceliano dos isolates foi: metconazol 0,07, protioconazol 0,1, e tebuconazol 0,19 mg/L. Para as misturas foi: protioconazol + trifloxistrobina 0,08, tebuconazol + trifloxistrobina 0,12, e metconazol + piraclostrobin 0,14 mg/L. Em relação a inibição da germinação dos esporos, a CI 50 para protioconazol + trifloxistrobina foi 0,06, para o tebuconazol + trifloxistrobina, 0,12 mg/L, e para os IQes isolados piraclostrobina, 0,09, e para a for trifloxistrobina, 0,28 mg/L. Demonstrou-se haver um diferença na sensibilidade entre os isolados e confirmou-se a elevada fungitoxicidade do protioconazol, metconazol e tebuconazol à F. graminearum. In Brazil, Fusarium head blight (FHB) affecting wheat can cause up to 39.8% damage. Resistant cultivars are not available yet; thus, short-term disease control relies on the use of fungicides. The first step to improve control is to monitor fungal populations that are sensitivity to chemicals in order to achieve efficient FHB management. In vitro experiments were conducted to evaluate the inhibitory concentration (IC 50 ) of fungi...
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