Sensitivity loss by Corynespora cassiicola, isolated from soybean, to the fungicide carbendazim

Abstract

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.

In vitro susceptibility of Corynespora cassiicola isolate from Brazil fields to fungicide

“…In this study, thecarbendazim treatment showed no significant difference for the isolate from Rio Doce and Laje farms, and for the Laje Farm, according to the IC 50 , this fungicide can be classified as moderately fungitoxic, according to the criteria proposed by Edgington et al (1971). Furthermore, Avozani et al (2014) found that the isolates of C. cassiicola showed less sensitivity to the carbendazim active ingredient and the cyproconazole active ingredient presented best valore of IC50. In studying the sensitivity of isolates submitted to the treatments, it was noted that the increased resistance of the isolates from the Laje Farm for some treatments, should necessitate the investigation of the previous management methods in this region that could have contribute to the multiplication of resistant populations.…”

“…It is known that the abuse of systemic molecules to control pathogens causes reduction in the sensitivity to products (Reis et al, 2010). In some studies, the fungicide carbendazim had low efficiency in controlling the target spot, which could have been as a result of the resistance to this chemical group on the pathogen (Teramoto et al, 2013;Avozani et al, 2014). However, in this work, carbendazim fungicide did not appear to be inefficient in its toxicity.…”

“…The plates were sealed with PVC plastic film and incubated in a growth chamber at 25 ± 2°C and 12 h photoperiod provided by three fluorescent 40 W lamps placed at 50 cm above the plates. When the colony in the control treatment reached the edge of the plates, the diameter of all colonies was measured with a digital calliper as described by Avozani et al (2014).…”

“…The inhibitory concentration (IC 50 ) studies for different fungicides and specific to C. cassiicola in soybean are scarce, yet it is very useful in carrying out research and sensitivity monitoring, especially in areas where the control of this disease is not being efficient (Avozani et al, 2014). The isolates from the Laje Farm treated with azoxystrobin + cyproconazole showed no significant effect on the IC 50 values but had high IC 50 value.…”

“…After these reports on the difficulty in the chemical control of the disease in recent harvests in the Midwest region of Brasil, some studies have shown a variability between populations of C. cassiicola and consequently the reduction or loss of the pathogen sensitivity to fungicides (Avozani et al, 2014;Teramoto et al, 2012;Soares et al, 2012). This response has occurred when successive applications of the same product are done in association with improper application conditions (eradicant applications, subdoses and inadequate technology) (Reis et al, 2010).…”