Wheat powdery mildew, Blumeria (= Erysiphe) graminis DC f sp tritici Marschal is one of the most important foliar diseases of cereals in Europe, and has shown a high potential for adaptability in sensitivity towards modern fungicides during the last 20 years. Quinoxyfen is a surface-mobile fungicide from a new chemical class that has been commercially used for the control of B graminis in Europe since 1997. When the compound was launched, a Resistance Management Strategy was implemented which included: no seed treatments, no autumn use, a specified window of application and recommendations for appropriate tank-mixing. To assess the success of this Management Strategy, a European-wide resistance monitoring programme was carried out between 1995 and 2000 using spore trap sampling, and a whole plant assay. The mean EC50 values found by year were 0.060 mg litre-1 in 1995, 0.052 mg litre-1 in 1996, 0.071 ml litre-1 in 1997, 0.039 mg litre-1 in 1998, 0.039 mg litre-1 in 1999 and 0.063 mg litre-1 in 2000. No new sensitivity classes were found. The slight shift to lower sensitivity in 1998 and 1999 was correlated with similar shifts in three wildtype isolates, and was ascribed to experimental variation. The monitoring programme will continue to assess the long-term impact of the management recommendations on the resistance status of quinoxyfen.
The population structure of Puccinia recondita f. sp. tritici ( Prt ) in western Europe was examined by assessing variability in pathogenicity and in randomly amplified polymorphic DNA (RAPD) among 61 single uredinial isolates. The isolates were chosen to represent pathotypes detected in a previous survey of pathogenic variability in the fungus in western Europe in 1995. Thirty‐five pathotypes were identified by assessing infection types produced by the 61 isolates on 24 differential lines, each with a single gene for resistance to Prt . In contrast, only 18 RAPD phenotypes were identified by scoring 19 polymorphic RAPD bands generated with eight RAPD primers. When analysed by cluster and bootstrap analyses, the pathogenicity and RAPD results revealed little evidence for robust distinct clusters among the isolates. Multiple isolates of several pathotypes collected from widely separated locations such as Belgium, Germany, France, Italy and Switzerland had the same RAPD phenotype, providing evidence of clonal migration over considerable distances in western Europe. Some variability (one or two band differences) was observed in RAPD phenotype within several pathotypes, indicating the possible occurrence of genetic changes independent of pathogenicity, and/or the independent development of pathotypes with different genetic backgrounds. Two groups of isolates identified in the 1995 survey, differentiated by pathogenicity for genes Lr3a , Lr3bg , Lr3ka and Lr30 , were not distinguished by RAPD phenotype, indicating that the groups probably do not constitute separate lineages within the pathogen population. Little correlation was apparent between the polymorphisms observed in pathogenicity and RAPD phenotypes. The similarity in the genetic backgrounds of the isolates, as assessed by RAPD markers, suggest that the observed differences in pathogenicity may have arisen by selection for specific virulences corresponding to genes for resistance in wheat cultivars grown in the region. Three isolates of pathotype 3, restricted in its distribution to southern France during 1995, were distinct from all other isolates in RAPD phenotype. Circumstantial evidence suggests that this pathotype originated from northern Africa, and that it belongs to a group of leaf rust pathogens specialized to durum wheats.
A single nucleotide polymorphism (SNP) in the cytochrome b gene confers resistance to strobilurin fungicides for several fungal pathogens. Therefore, on the basis of a change at amino acid position 143 from glycine to alanine, a real-time PCR assay was established for the quantitative detection of the analogous SNP in the cytochrome b sequence of Pyrenophora teres Drechsler, which causes barley net blotch. Allelic discrimination was achieved by using allele specific primers with artificially mismatched nucleic acid bases and minor groove binding probes. Validation parameters for the lower limits of the working range, namely limits of detection (LOD) and limits of quantification (LOQ), were statistically determined by the variance of calibration data, as well as by the variance of the 100% non-strobilurin-resistant allele DNA sample (blank values). It was found that the detection was limited by the variance of blank values (five in 801 458 copies; 0.0006%), whereas the quantification was limited by the variance of calibration data (37 in 801 458 copies; 0.0046%). The real-time PCR assay was finally used to monitor strobilurin-resistant cytochrome b alleles in barley net blotch field samples, which were already classified in in vivo biotests to be fully sensitive to strobilurins. All signals for strobilurin-resistant cytochrome b alleles were below the LOD, and therefore the results are in total agreement with the phenotypes revealed by biotests.
Corrigendum to: Goll MB, Schade-Schütze A, Swart G et al., 2014. Survey on the prevalence of Rhizoctonia spp. in European soils and determination of the baseline sensitivity towards sedaxane. Plant Pathology 63, 148–154. doi: 10.1111/ppa.12063. There is an error in Table 1 for the percentage of soil samples from the UK, Poland and Spain from which Rhizoctonia solani was isolated. The data in column 3 are also percentage values not numbers of samples. The correct Table 1 is as follows.
