Strobilurin (QoI) Resistance in Populations of Erysiphe necator on Grapes in Michigan

Abstract

Powdery mildew, caused by Erysiphe necator, is the most common and destructive disease of grapes (Vitis spp.) worldwide. In Michigan, it is primarily controlled with fungicides, including strobilurins (quinone outside inhibitors [QoIs]). Within the United States, resistance to this class of fungicides has been reported in E. necator populations in some east coast states. Among 12 E. necator isolates collected from five Michigan vineyards in 2008, one carried the G143A single-nucleotide mutation responsible for QoI resistance. This isolate was confirmed to be resistant in a conidium germination assay on water agar amended with trifloxystrobin at 0.001, 0.01, 0.1, 1, 10, or 100 μg/ml and salicylhydroxamic acid (100 mg/liter). The mutant isolate was able to germinate on media amended with 100 μg/ml trifloxystrobin, whereas a representative wild-type isolate did not germinate at concentrations higher than 0.1 μg/ml. In 2009, 172 isolates were collected from a total of 21 vineyards (juice and wine grapes): three vineyards with no fungicide application history (baseline sites), six research vineyards, and 12 commercial vineyards. QoI resistance was defined as the effective concentration that inhibited 50% of conidial germination (EC50) > 1 μg/ml. Isolates from baseline sites had EC50 values mostly below 0.01 μg/ml, while isolates that were highly resistant to trifloxystrobin (EC50 > 100 μg/ml) occurred in five research and three commercial wine grape vineyards at frequencies of 40 to 100% and 25 to 75% of the isolates, respectively. The G143A mutation was detected in every isolate with an EC50 > 1 μg/ml. These results suggest that fungicide resistance may play a role in suboptimal control of powdery mildew observed in some Michigan vineyards and emphasizes the need for continued fungicide resistance management.

Identification and characterization of new mutations in mitochondrial cytochrome b that confer resistance to bifenazate and acequinocyl in the spider miteTetranychus urticae

“…In this study, we discovered a G132A mutation in cytochrome b of T. urticae , equivalent to G143A in fungi, which has been reported as the most frequent mutation associated with strobilurin resistance . During a survey investigating the frequency of G132A in T. urticae field strains, we also uncovered for the first time the combination of G126S + A133T in T. urticae , reported previously in the spider mite P. citri .…”

Distribution of QoI Resistance in Populations of Tangerine-Infecting Alternaria alternata in Florida

“…No relationship was observed between Qol exposures per year and field disease severity categories. The G143A mutation is related to control failure of Qol fungicides (20), such as observed for A. alternata in pistachio (40), V. inaequalis in apple (37), E. necator in grape (41), Cercospora beticola in sugar beet (9), Botrytis cinérea in multiple crops (17,29,36), and others. Likewise, our results showed a lack of relationship between resistant isolates and vimlence.…”

Fitness ofErysiphe necatorwith G143A-Based Resistance to Quinone Outside Inhibitors

“…Practical resistance, which indicates observed loss of control in field conditions (4), in E. ne cator was first reported in New York and Pennsylvania (49). Wide spread resistance was later reported present in Virginia (3,7), Michigan (36), and Europe (21). Qol resistance poses a challenge for effective disease control; thus, it is important to determine whether it is possible to devise strategies to extend the usefulness of Qols as a major component of disease management in grape vines.…”

“…Three mutations-G143A, F129L, and G137R-are associated with naturally occurring Qol-resistant pathogens (34). The G143A mutation has been detected in a num ber of pathogens (21), including E. necator isolates from the United States (3,7,36), and is associated with high resistance fac tors (26). The F129L substitution confers lower levels of resistance (37,47) in Pyricularia grisea (31), Pythium aphanidermatum (26), Pyrenophora sp.…”