Effect of the F129L Mutation in Alternaria solani on Fungicides Affecting Mitochondrial Respiration

Abstract

Isolates of Alternaria solani previously collected from throughout the Midwestern United States and characterized as being azoxystrobin sensitive or reduced sensitive were tested for sensitivity to the Quinone outside inhibitor (QoI) fungicides famoxadone and fenamidone and the carboxamide fungicide boscalid. All three fungicides affect mitochondrial respiration: famoxadone and fenamidone at complex III, and boscalid at complex II. A. solani isolates possessing reducedsensitivity to azoxystrobin also were less sensitive in vitro to famoxadone and fenamidone compared with azoxystrobin-sensitive isolates, but the shift in sensitivity was of lower magnitude, approximately 2- to 3-fold versus approximately 12-fold for azoxystrobin. The in vitro EC50 values, the concentration that effectively reduces germination by 50% relative to the untreated control, for sensitive A. solani isolates were significantly lower for famoxadone and azoxystrobin than for fenamidone and boscalid; whereas, for reduced-sensitive isolates, famoxadone EC50 values were significantly lower than all other fungicides. Isolates of A. solani with reducedsensitivity to azoxystrobin were twofold more sensitive in vitro to boscalid than were azoxystrobin-sensitive wild-type isolates, displaying negative cross-sensitivity. All isolates determined to have reduced-sensitivity to azoxystrobin also were determined to possess the amino acid substitution of phenylalanine with leucine at position 129 (F129L mutation) using real-time polymerase chain reaction. In vivo studies were performed to determine the effects of in vitro sensitivity shifts on early blight disease control provided by each fungicide over a range of concentrations. Reduced-sensitivity to azoxystrobin did not significantly affect disease control provided by famoxadone, regardless of the wide range of in vitro famoxadone EC50 values. Efficacy of fenamidone was affected by some azoxystrobin reduced-sensitive A. solani isolates, but not others. Boscalid controlled azoxystrobin-sensitive and reduced-sensitive isolates with equal effectiveness. These results suggest that the F129L mutation present in A. solani does not convey cross-sensitivity in vivo among all QoI or related fungicides, and that two- to threefold shifts in in vitro sensitivity among A. solani isolates does not appreciably affect disease control.

Ex Vivo Application of Secreted Metabolites Produced by Soil-Inhabiting Bacillus spp. Efficiently Controls Foliar Diseases Caused by Alternaria spp

“…Target organisms can develop resistance to single-site antimicrobial compounds very rapidly, and in most cases resistance is traced back to a single genetic mutation in the target molecule that leads to a loss of recognition or metabolism of the antimicrobial compound. For example, A. solani has developed resistance to several commonly used fungicides, including azoxystrobin, due to single amino acid changes in the target molecules (8,11,(61)(62)(63). Resistance is often attributed to frequent use of antimicrobial compounds of the same class.…”

Salts Application for Suppressing Potato Early Blight Disease

“…Estimating total annual crop losses due to any particular disease is difficult to do accurately. Values in the literature for crop losses due to early blight vary enormously from 5 to 78% (Waals et al 2004;Pasche et al 2004Pasche et al , 2005.…”

Detection of Fungicide Resistance

“…Resistance has been reported in all major continents: Asia, Australia, Europe, North America, and South America (FRAC 2006;Wilson and Wicks, 2011). The majority of the reports associate the point mutation that results in a change from glutamate to alanine at codon 143 (G143A), followed by the resistance that results from a transition from phenylalanine to leucine at position 129 (F129L) (Pasche et al 2005;Sierotzki et al 2007); the least commonly observed mutation involves a change from glycine to arginine at position 137 (G137R) (Sierotzki et al 2007), and of course, unknown causes (Lesniak et al 2011). These easily identified mutations allow for the rapid detection for the potential of QoI-resistance in a variety of fungi and Chromista.…”