Resistance to Q_oI (Strobilurin-like) Fungicides in Isolates of Pyricularia grisea from Perennial Ryegrass

Abstract

In August 2000, azoxystrobin was ineffective in controlling gray leaf spot of perennial ryegrass at a golf course in Lexington, KY and at two golf courses in Illinois. Isolates suspected of being fungicide-resistant (“suspect isolates”) were compared to “baseline” isolates obtained from sites with no known use of quinol-oxidizing inhibitor (QoI) fungicides. Conidial germination of Pyricularia grisea was tested in vitro with 100 μg of salicylhydroxamic acid per ml. For baseline isolates, 50% effective concentration (EC50) values for azoxystrobin and trifloxystrobin were 0.015 to 0.064 and 0.013 to 0.078 μg/ml, respectively; EC50 values for suspect isolates were 2.39 to 44.8 and 0.31 to 111, respectively. All suspect isolates exhibited significantly (P = 0.05) lower sensitivity to QoI fungicides than all baseline isolates. The mean EC50 values for suspect isolates for azoxystrobin and trifloxystrobin were 690 and 827 times higher, respectively, than the means for baseline isolates. In the laboratory, azoxystrobin and trifloxystrobin provided essentially complete control of disease induced by nine baseline isolates in vivo. Azoxystrobin and trifloxystrobin provided poor to no control of disease induced by six of eight suspect isolates; control of disease induced by the remaining two isolates was partial for azoxystrobin and complete for trifloxystrobin. We conclude that one or more biotypes of perennial ryegrass-infecting strains of P. grisea with resistance to QoI fungicides have emerged. This is the first report of resistance to QoI fungicides in P. grisea. Furthermore, this is one of two QoIresistant fungal pathogens collected in the United States during the 2000 growing season, the first instances reported for North America.

Late Blight of Potato (Phytophthora infestans) I: Fungicides Application and Associated Challenges

“…Several studies document those different fungicides once highly effective in suppressing P. infestans before the 1980s have now lost their efficacy of controlling late blight in different parts of the world (Goodwin et al, 1998;Yuan et al, 2006). Vincelli and Dixon (2002) argues that there are two types of resistance development -qualitative and quantitative-in pathogen towards fungicides. In quantitative resistance, new variants show comparatively less sensitivity to fungicides than their parental types.…”

“…This type of resistance can be overcome by increasing the dose and spray frequency of fungicides. On the other hand in qualitative resistance, progenies show greater resistance to fungicides than their parents and cannot be compromised by increasing dose rate and frequency of fungicide spray (Vincelli and Dixon, 2002). Reports of increased number of isolates and cases of resistance development to fungicides are generally assigned to the appearance of new genotypes.…”

“…Similarly, spray of multi-site fungicides are considered as low contributing factor in resistance development than site specific fungicides (Gisi and Sierotzki, 2008). Reducing the spray frequencies and enhancing the spray intervals, alternative application of different group of fungicides in a growing season can manage the risk (Vincelli and Dixon, 2002). Up gradation of existing fungicides or formulation of new ones on the basis of resistance risk surveys generally are helpful tactics to overcome the resistance development risks for some years.…”

Cotton in Brazil: Importance and Chemical Control of Bolls Rot

“…These compounds belong to the group of the quinone outside inhibitors (QoI) or group 11 fungicides, whose toxicity arises from the inhibition of the mitochondrial respiratory chain at Complex III level, preventing the biochemical chain of electron transfer at the site of mitochondria, interfering with respiration of the pathogen (Ghini & Kimati 2000). They are typically absorbed by the cuticle of the fungus, acting as protectant fungicides (Vincelli & Dixon, 2002).…”

Phylogenetic diversity and sensitivity to MBI and QoI fungicides of <i>Magnaporthe oryzae</i> in Taiwan

“…21) Moreover, azoxystrobin and trifloxystrobin were used to control ryegrass disease caused by P. grisea, however, the two strobilurin fungicides lost its efficacy in controlling P. grisea. 30) In Taiwan, strobilurin fungicides are commonly used for controlling powdery or downy mildew of cucumber, downy mildew of crucifer, late blight of tomato and potato, rust disease of allium, anthracnose of fruits and other fungal diseases of fruits. 22) Previous studies demonstrated that the isolates of Botrytis cinerea from strawberry and Colletotrichum gloeosporioides from mango and strawberry showed low sensitivity to kresoxim-methyl, azoxystrobin and triflorstrobin.…”