Location: Grape Genetics ResearchTitle: Selection, fitness, and control of grape isolates of Botrytis cinerea variably sensitive to fenhexamid Author
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2014
Publication Date: 1/24/2014
Citation: Saito, S., Cadle Davidson, L.E., Wilcox, W. 2014. Selection, fitness, and control of grape isolates of Botrytis cinerea variably sensitive to fenhexamid. Plant Disease. 98:233-240. Interpretive Summary: Thirty-one of 683 Botrytis cinerea isolates collected from a fungicide-trial vineyard appeared to be resistant to fenhexamid fungicide. In Petri dish culture, all resistant isolates suffered reductions in growth and/or sporulation, relative to sensitive isolates. We tested whether fenhexamid at 25 to 100% of the recommended rate could reduce disease when applied to grape berries before or after infection. All treatments significantly delayed disease onset and progress caused by sensitive isolates, but provided little to no control of resistant isolates. In the most resistant isolate, we discovered a previously unreported mutation in the enzyme that fenhexamid targets. This research benefited from a qPCR technology to quantify fungal growth within berries. In the vineyard, disease control was affected by the number and rate of fenhexamid applications, but resistant isolates were not preferentially selected by any particular treatment.
Technical Abstract: Of 683 Botrytis cinerea isolates collected from a fungicide-trial vineyard, 31 were classified as putatively resistant to fenhexamid (EC50 =0.1 ug/ml). For the resistant isolates that survived and sporulated in culture, colony expansion and conidial germination frequency was significantly reduced relative to the mean of 30 representative baseline isolates (EC50 = 0.03 ug/ml). Grape berries were inoculated with four isolates representing a range of fenhexamid sensitivities and treated preventively or curatively with fenhexamid concentrations (150-600 mg/L) representing 25 to 100% of the recommended rate. All treatments significantly delayed disease onset and progress caused by isolates with EC50 values of 0.03 and 0.15 ug/ml, but provided little to no control of isolates with EC50 values of 0.32 and 62.5 ug/ml. The latter isolate exhibited a previously unreported F427V mutation of ERG27, an enzyme of ergosterol biosynthesis. In a duplex qPCR test, the ratio of pathogen/host DNA increased significantly for 14 days after inoculation of untreated berries with a baseline isolate, but declined slightly in berries treated with 600 mg/L fenhexamid 1 day post-inoculation. In the vineyard, disease control was affected by the number and rate of fenhexamid applications, but B. cinerea isolates with EC50 = 0.1 ug/ml were not preferentially selected.