Field efficacy of pyraclostrobin against populations of Pyrenophora teres containing the F129L mutation in the cytochrome b gene

Journal of Plant Diseases and Protection - Resistance of plant pathogenic fungi towards QoI fungicides is mainly caused by two mutations in the cytochrome b gene, the F129L and G143A. In...     

Mutations in target genes of succinate dehydrogenase inhibitors and demethylation inhibitors in Ramularia collo-cygni in Europe

Journal of Plant Diseases and Protection - Ramularia collo-cygni is a devastating plant pathogen of barley with an increasing importance in Europe and several other barley growing regions...     

Baseline and differential sensitivity of Peronophythora litchii (lychee downy blight) to three carboxylic acid amide fungicides

Downy blight, caused by Peronophythora litchii, is an important disease of lychee (litchi) plants in China. The in vitro sensitivities of various asexual stages of P. litchii to the three carboxylic acid amide (CAA) fungicides dimethomorph, flumorph and pyrimorph were studied with four single‐sporangium isolates. None of the three fungicides affected zoospore discharge from sporangia, but they strongly inhibited mycelial growth (mean EC₅₀ values of 0·075, 0·258 and 0·115 mg L^?1, respectively); sporangial production (mean EC₅₀ values of 0·085, 0·315 and 0·150 mg L^?1, respectively); germination of cystospores (mean EC₅₀ values of 0·140, 0·150 and 0·645 mg L^?1, respectively); and germination of sporangia (mean EC₅₀ values of 0·203, 0·5 and 0·743 mg L^?1, respectively). As mycelial growth was the most sensitive stage to dimethomorph and pyrimorph, it was chosen to test baseline sensitivities to the three fungicides. In 2007, from 131 isolates collected in Fujian, Guangdong and Guangxi provinces, 127, 116 and 113 isolates were used to establish baseline sensitivity for dimethomorph, flumorph and pyrimorph respectively. Isolates from different provinces exhibited similar baseline sensitivity to the same fungicide. Baseline sensitivities to dimethomorph, flumorph and pyrimorph were distributed as unimodal curves, with mean EC₅₀ values of 0·082 (± 0·01), 0·282 (± 0·047), and 0·115 (± 0·032) mg L^?1, respectively. This information will serve as a baseline for tracking future changes in sensitivities of P. litchii populations to these three CAA fungicides.     

Proposal for a unified nomenclature for target‐site mutations associated with resistance to fungicides

Evolved resistance to fungicides is a major problem limiting our ability to control agricultural, medical and veterinary pathogens and is frequently associated with substitutions in the amino acid sequence of the target protein. The convention for describing amino acid substitutions is to cite the wild‐type amino acid, the codon number and the new amino acid, using the one‐letter amino acid code. It has frequently been observed that orthologous amino acid mutations have been selected in different species by fungicides from the same mode of action class, but the amino acids have different numbers. These differences in numbering arise from the different lengths of the proteins in each species. The purpose of the present paper is to propose a system for unifying the labelling of amino acids in fungicide target proteins. To do this we have produced alignments between fungicide target proteins of relevant species fitted to a well‐studied ‘archetype’ species. Orthologous amino acids in all species are then assigned numerical ‘labels’ based on the position of the amino acid in the archetype protein. © 2016 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Editorial

Journal of Plant Diseases and Protection -     

Decreasing azole sensitivity of Z. tritici in Europe contributes to reduced and varying field efficacy

Journal of Plant Diseases and Protection - Septoria tritici blotch (STB; Zymoseptoria tritici) is the most important leaf disease of wheat in Northern and Western Europe. The problem of fungicide...     

Sensitivity of Mycosphaerella graminicola (anamorph: Septoria tritici) to DMI fungicides across Europe and impact on field performance

Since the occurrence and spread of resistance to quinone outside inhibitors (QoI) in Mycosphaerella graminicola in the early 2000s in Europe, demethylation inhibitors (DMIs) form the backbone for control of Septoria leaf blotch. European monitoring studies, carried out by various research institutes and DMI manufacturers, have shown a shift of the European M. graminicola population towards increased ED₅₀ values for DMI fungicides. Populations of M. graminicola consist of very heterogeneous isolates within a region, and even within a field, in terms of DMI sensitivity. Sensitivity to DMIs is influenced by the haplotype of CYP51, the target of DMIs. New CYP51‐haplotypes have emerged and the frequency of less sensitive haplotypes in Europe has increased in recent years. Studies with efflux transporter inhibitors showed that not only CYP51, but also enhanced efflux, may play a role in the DMI sensitivity response. Sensitivity studies with 5 DMIs registered for Septoria leaf blotch control indicated that sensitivity of isolates to the 5 DMIs is heterogeneous and the overall correlation of sensitivity to the different DMIs is poor. A key requirement for sustainable control and resistance management of Septoria leaf blotch is therefore the continued availability of different DMIs.     

Mutations in sdh genes in field isolates of Zymoseptoria tritici and impact on the sensitivity to various succinate dehydrogenase inhibitors

Zymoseptoria tritici is the causal agent of septoria tritici blotch (STB), a foliar wheat disease important worldwide. Succinate dehydrogenase inhibitors (SDHIs) have been used in cereals for effective control of STB for several years, but resistance towards SDHIs has been reported in several phytopathogenic fungi. Resistance mechanisms are target‐site mutations in the genes coding for subunits B, C and D of the succinate dehydrogenase (SDH) enzyme. Previous monitoring data in Europe indicated the presence of single isolates of Z. tritici with reduced SDHI sensitivity. These isolates carried mutations leading to amino acid exchanges: C‐T79N, C‐W80S in 2012; C‐N86S in 2013; B‐N225T and C‐T79N in 2014; and C‐V166M, B‐T268I, C‐N86S, C‐T79N and C‐H152R in 2015. The current study provides results from microtitre and greenhouse experiments to give an insight into the impact of different mutations in field isolates on various SDHIs. In microtitre tests, the highest EC₅₀ values for all tested SDHIs were obtained with mutants carrying C‐H152R. Curative greenhouse tests with various SDHIs confirmed the findings of microtitre tests that isolates with C‐H152R are, in general, controlled with lower efficacy than isolates carrying B‐T268I, C‐T79N and C‐N86S. SDHI‐resistant isolates of Z. tritici found in the field were shown to have cross‐resistance towards all SDHIs tested. So far, SDHI‐resistant isolates of Z. tritici have been found in low frequencies in Europe. Therefore, FRAC recommendations for resistance management in cereals, including a limited number of applications, alternation and combination with other MOAs, should be followed to prolong SDHI field efficacy.