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Site-specific high throughput monitoring of airborne ascospores of Venturia inaequalis, the causal agent of apple scab, can improve existing warning systems. A new qPCR assay was developed to quantify ascospores collected by a simple rotating-arm spore sampler. The qPCR assay was highly specific and sensitive, with a limit of quantification of 20 ascospores per sample. The new detection system was compared to sampling with a traditional Burkard volumetric spore trap and to microscopic quantification. During controlled ascospore release experiments in a closed environment, strong correlations (ρ: 0.96 to 0.99) were observed between the two types of samplers and the two methods of quantification but significantly larger numbers of spores (log difference: 0.43 to 0.69) were obtained when using the rotating-arm sampler and when using molecular quantification. During comparisons under outdoor conditions over a three-year period, reasonable correlations between the techniques (average ρ = 0.61) were observed. When rotating-arm samplers operate continuously they can get saturated but their counts still correlated better with those from the Burkard sampler than when they only operate during rain and until two hours after. This suggests that ascospores were also captured outside of rain events. Based on these comparisons, molecular quantification of spores captured with the rotating-arm sampler appears to be a sensitive and reliable method to determine airborne ascospores of V. inaequalis and holds promise as a tool to guide targeted fungicide applications in commercial orchards as well as to increase our knowledge of the aerobiology of this pathogen. [ABSTRACT FROM AUTHOR]

An international test performance study (TPS) was organised to generate validation data for three molecular Synchytrium endobioticum tests: van den Boogert et al. (European Journal of Plant Pathology 113, 47-57, 2005), and van Gent-Pelzer et al. (European Journal of Plant Pathology, 126, 129-133, 2010) for the detection of S. endobioticum, and the pathotype 1(D1) identification test described by Bonants et al. (European Journal of Plant Pathology, 143, 495-506, 2015). Two TPS rounds were organised focussing on different test matrices, i.e. round 1: warted potato tissue, and round 2: resting spore suspensions. When using the tests for detection and identification of S. endobioticum in warted potato tissue, no significant differences were observed for diagnostic sensitivity, diagnostic specificity, overall accuracy, analytical sensitivity and robustness. When using the tests for detection and identification of S. endobioticum in resting spore suspensions, the van den Boogert and van Gent-Pelzer tests significantly outperform the Bonants test for diagnostic sensitivity and diagnostic specificity. For overall accuracy and analytical sensitivity, the van Gent-Pelzer significantly outperforms the van den Boogert and Bonants tests and is regarded as the test of choice when identifying S. endobioticum from resting spores. Tests regarded fit for purpose for routine testing of wart material and resting spore suspensions are proposed for the update of EPPO standard PM7/28(1) Synchytrium endobioticum. [ABSTRACT FROM AUTHOR]

Fusarium foetens is a recently described aggressive vascular pathogen of Begonia x hiemalis. Since 2004, it has caused severe losses for Begonia growers in Northern Europe and North America. F. foetens is likely to be of exotic origin. Little is known about the accumulation of the fungus in Begonia plants before and during symptom expression and about its host range. We have optimised a molecular detection method for F. foetens by only using the plant part containing the largest amount of the pathogen and by optimising the tissue maceration and DNA extraction techniques. This allowed a reliable detection limit of 2310 spore equivalents per plant and a theoretical detection limit of as low as 84 to 167 spore equivalents per plant. Using this method, we demonstrated exponential accumulation of F. foetens DNA in Begonia roots, resulting in symptoms at a threshold of approximately 10 spore equivalents and levelling off at 10 spore equivalents per plant. The observed rate of accumulation and the amount of pathogen DNA in non-symptomatic plants can be combined to determine whether the cuttings were infected after delivery at the Begonia nursery and to calculate the estimated timing of symptom development. To test the host range, we applied the optimised molecular detection technique. During these tests, only Begonia x hiemalis plants became symptomatic, but many other plant species supported growth of the pathogen. This information can be used to aid pathogen control and has implications for pest risk assessment. [ABSTRACT FROM AUTHOR]

Puccinia horiana is the causal agent of chrysanthemum white rust or Japanese rust. This microcyclic autoecious rust has a quarantine status and can cause major damage in the commercial production of Chrysanthemum x morifolium. Given the international and often trans-continental production of planting material and cut flowers of chrysanthemum and the decreasing availability of registered fungicides in specific regions, breeding for resistance against P. horiana will gain importance and will need to involve the appropriate resistance genes for the pathotypes that may be present. As pathotypes have not been well characterized in this system, the main objective was to build an international collection of isolates and screen these on a large collection of cultivars to identify different pathotypes. Using a robust and high throughput bioassay, we tested 36 selected cultivars with 22 individual single-pustule isolates of P. horiana. The isolates originated from three different continents over 4 different collection years and included some isolates from cultivars previously reported as resistant. In most cases the bioassays resulted in a clear scoring of interaction phenotypes as susceptible or resistant, while in several cases consistent intermediate phenotypes were found, often on specific cultivars. Twenty-four of the cultivars gave a differential interaction phenotype profile. All isolates produced a unique profile, infecting a minimum of 4 and a maximum of 19 differential cultivars. Based on the Person analysis of these profiles, this pathosystem contains at least seven resistance genes (and seven avirulence genes), demonstrating the highly complex race structure in this pathosystem. [ABSTRACT FROM AUTHOR]

Phytophthora ramorum, a recently described North American and European pathogen, has three clonal lineages. The NA1 and NA2 lineages are found in North American forests and nurseries, while the EU1 lineage appears mainly in European nurseries. P. ramorum is heterothallic, having two mating types A1 and A2. All NA1 and NA2 isolates are of A2 mating type. When first collected, all EU1 isolates were of A1 mating type, with the exception of one A2 isolate collected in Belgium in 2002. Screening 410 other Belgian isolates for mating type revealed two additional EU1-A2 isolates collected in 2002 and 2003. PCR-RFLP, AFLP and SSR markers were used to determine the nature of the mating type change. The three isolates show no indications of sexual recombination or mitotic crossing over, indicating that mutation or mitotic gene conversion is the most likely explanation for the mating type change. We compared the pathogenicity and sporulation characteristics of the EU1-A2 isolates to those of EU1-A1 and NA1-A2 isolates on four host plants. Despite small differences in pathogenicity on some hosts, the EU1-A2 isolates were similarly aggressive to each other and to the EU1-A1 isolates and more aggressive than the NA1-A2 isolates. Sporulation characteristics were also comparable among EU1-A2 isolates and between EU1-A1 and EU1-A2 isolates, except for EU1-A2 isolate BBA 26/02. The limited genotypic and phenotypic differences between EU1-A2 isolates probably evolved after the mating type change, which may have occurred several years before the isolates were detected. There are strong indications that the EU1-A2 population has been eradicated from Belgium. [ABSTRACT FROM AUTHOR]