Emergence and early evolution of fungicide resistance in North American populations of Zymoseptoria tritici

Although fungicide resistance in crop pathogens is a global threat to food production, surprisingly little is known about the evolutionary processes associated with the emergence and spread of fungicide resistance. Early stages in the evolution of fungicide resistance were evaluated using the wheat pathogen Zymoseptoria tritici, taking advantage of an isolate collection spanning 20 years in Oregon, USA, and including two sites with differing intensity of fungicide use. Sequences of the mitochondrial cytb protein conferring single‐mutation resistance to QoI fungicides and the nuclear CYP51 gene implicated in multiple‐mutation resistance to azole fungicides were analysed. Mutations associated with resistance to both fungicides were absent in the 1992 isolates, but frequent in the 2012 collection, with higher frequencies of resistance alleles found at the field site with more intensive fungicide use. Results suggest that the QoI resistance evolved independently in several lineages, and resulted in significant mitochondrial genome bottlenecks. In contrast, the CYP51 gene showed signatures of diversifying selection and intragenic recombination among three phylogenetic clades. The findings support a recent emergence of resistance to the two fungicide classes in Oregon, facilitated by selection for mutations in the associated resistance genes.     

First report of QoI resistance in Italian population of Pyricularia oryzae

Journal of Plant Diseases and Protection - Rice blast disease, caused by Pyricularia oryzae Cavara, is considered the most destructive rice disease in Italy. Quinone outside inhibitor (QoI)...     

Detection of Ramularia collo-cygni DMI- and SDHI-resistant field populations in Austria and the effect of fungicides on the population and genetic diversity

European Journal of Plant Pathology - Winter barley (Hordeum vulgare L.) is the third most cultivated crop after corn and wheat in Austria but one of the most challenging for disease control. The...     

Phylogenetic analysis of ORF5 and ORF7 sequences of porcine reproductive and respiratory syndrome virus (PRRSV) from PRRS-positive Italian farms: a showcase for PRRSV epidemiology and its consequences on farm management

We investigated the dynamics of porcine reproductive and respiratory syndrome virus (PRRSV) variability in a range of swine PRRS-positive farms located in Northern Italy, to provide insights into the epidemiology and diffusion of the virus, particularly throughout the entire swine production chain. In this context, we also examined the effectiveness and the critical points of a recently developed gilts acclimatization program in swine breeder farms. To achieve these aims, we designed new primers and determined 64 complete open reading frame 5 (ORF5) sequences, representing Italian PRRSV field strains and the European vaccine Porcilis strain (Intervet); in addition, the more conserved ORF7 of 11 PRRSV strains were sequenced. The domains' prediction of their putative protein sequences was performed as well. Based on these sequences, phylogenetic trees were inferred which revealed a high degree of variability among the PRRSV Italian strains. The outcomes of the phylogenetic analysis showed that the most frequent source of infection in PRRS-positive farms (sow herds, nursery sites, fattening units) was the introduction of animals carrying a new variant and not the modification of already present variants; moreover, the integration of data from phylogenetic analysis and from the clinical and serological status of the swine herds suggested that the acclimatization program could be a valid tool to stabilize the PRRS clinical picture in farms, only when applied in combination with rigorous bio-security routine management and avoid the incoming of new PRRSV variants.     

QoI resistance emerged independently at least 4 times in European populations of Mycosphaerella graminicola

BACKGROUND: QoI fungicides or quinone outside inhibitors (also called strobilurins) have been widely used to control agriculturally important fungal pathogens since their introduction in 1996. Strobilurins block the respiration pathway by inhibiting the cytochrome bc1 complex in mitochondria. Several plant pathogenic fungi have developed field resistance. The first QoI resistance in Mycosphaerella graminicola (Fuckel) Schroter was detected retrospectively in UK in 2001 at a low frequency in QoI-treated plots. During the following seasons, resistance reached high frequencies across northern Europe. The aim of this study was to identify the main evolutionary forces driving the rapid emergence and spread of QoI resistance in M. graminicola populations.RESULTS: The G143A mutation causing QoI resistance was first detected during 2002 in all tested populations and in eight distinct mtDNA sequence haplotypes. By 2004, 24 different mtDNA haplotypes contained the G143A mutation. Phylogenetic analysis showed that strobilurin resistance was acquired independently through at least four recurrent mutations at the same site of cytochrome b. Estimates of directional migration rates showed that the majority of gene flow in Europe had occurred in a west-to-east direction.CONCLUSION: This study demonstrated that recurring mutations independently introduced the QoI resistance allele into different genetic and geographic backgrounds. The resistant haplotypes then increased in frequency owing to the strong fungicide selection and spread eastward through wind dispersal of ascospores.     

Fungicide strategies and resistance of Ramularia collo-cygni to demethylation and succinate dehydrogenase inhibitors in Austrian winter barley (Hordeum vulgare)

Journal of Plant Diseases and Protection - Ramularia collo-cygni B. Sutton and J.M. Waller is a major disease in Austrian barley-growing regions. To date, fungicide application is the most...