Oospores progenies from Phytophthora ramorum.
ABSTRACT Oospores of Phytophthora ramorum were produced from intraspecific pairings between a European A1 and European or American A2 strains. Their viability was evaluated through colouration with tetrazolium bromide. The distribution of oospores in the different classes of colouration was similar to that found in other Phytophthora species (homothallic and heterothallic): most of the oospores stained purple, which corresponds to spores in dormancy. In order to produce single-oospore cultures, a method was developed to separate oospores from mycelium and chlamydospores. Germination of oospores was observed in 110, 250, 350 and 500-d-old cultures at a low proportion. Microsatellite marker analyses on oospore progenies revealed that the oospores resulted from hybridisation. More than 50 oospore progenies were characterised in terms of mating type, aggressiveness on Rhododendron leaves, and growth rate on two different media. The results are discussed in the context of pest risk analysis.
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ABSTRACT: It is becoming increasingly evident that interspecific hybridization is a common event in phytophthora evolution. Yet, the fundamental processes underlying interspecific hybridization and the consequences for its ecological fitness and distribution are not well understood. We studied hybridization events in phytophthora clade 8b. This is a cold-tolerant group of plant pathogenic oomycetes in which six host-specific species have been described that mostly attack winter-grown vegetables. Hybrid characterization was done by sequencing and cloning of two nuclear (ITS and Ypt1) and two mitochondrial loci (Cox1 and Nadh1) combined with DNA content estimation using flow cytometry. Three different mtDNA haplotypes were recovered among the presumed hybrid isolates, dividing the hybrids into three types, with different parental species involved. In the nuclear genes, additivity, i.e. the presence of two alleles coming from different parents, was detected. Hybrid isolates showed large variations in DNA content, which was positively correlated with the additivity in nuclear loci, indicating allopolyploid hybridization followed by a process of diploidization. Moreover, indications of homeologous recombination were found in the hybrids by cloning ITS products. The hybrid isolates have been isolated from a range of hosts that have not been reported previously for clade 8b species, indicating that they have novel pathogenic potential. Next to this, DNA content measurements of the non-hybrid clade 8b species suggest that polyploidy is a common feature of this clade. We hypothesize that interspecific hybridization and polyploidy are two linked phenomena in phytophthora, and that these processes might play an important and ongoing role in the evolution of this genus.PLoS ONE 01/2013; 8(12):e85385. · 3.53 Impact Factor
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ABSTRACT: Although most plant diseases are the result of natural or unintentional causes, cropping systems and essential natural plant resources such as forests and grasslands also are considered vulnerable to actions of nefarious intent. Microbial forensics is defined as the application of scientific approaches to solving a crime that involves a microorganism; its goal is to investigate and present unbiased scientific evidence useful for attributing the crime to a perpetrator. Recent programs intended to enhance general capabilities in microbial forensics have included specific attention to plant pathogens. Compared to the strategies employed by traditional plant disease diagnosticians, forensic applications of plant pathogen diagnostics require unusually high levels of stringency, reliability, and prior vali-dation. These assays must be paired with court-defensible sampling methods, chain of custody, and other traditional and non-traditional methods of forensic investigation., © Springer Science+Business Media Dordrecht 2014 103 Forensics and Plant Pathology – Synergy of Two Disciplines Forensic plant pathology is a blend of the disciplines of plant pathology and forensic science that supports the investigation of plant diseases and pathogens by providing unbiased scientific methodology and evidence for criminal attribution. Important to this effort are traceback strategies for determining pathogen origin and movement pathway(s) as well as the possible role of human intent. Plant pathology and forensic science find a common arena with other disciplines within the realm of agricultural biosecurity, which includes science-based policies, measures and reg-ulatory frameworks for reacting to and managing risks associated with food, agriculture, forestry, and the environmental (UN 2002). The concept also includes other areas of environmental risk such as aquatic systems, and strongly associated sectors such as human health, justice and defense (Ochoa-Corona 2011). Unwanted movement of plant pathogens and pests into the agricultural sector can take place by various means including wind, water, insects, international commerce and travel. Such movement occurs frequently as inadvertent introduction of exotic pathogens and pests; however smuggling and illegal trade are examples of relevant criminal activities. In such situations multidisciplinary teams including representatives of the diagnostic, regulatory, and law enforcement communities must work in coor-dination to achieve the most effective response (Fig. 1). More creative strategies for both vertical and horizontal communication among the involved biosecurity and law enforcement agencies are needed (Ochoa-Corona 2011).Detection and Diagnostics of Plant Pathogens. Series: Plant Pathology in the 21st Century, Vol. 5., 1st edited by Maria Lodovica Gullino, Peter J M Bonants, 01/2014: chapter 7: pages 103-115; Springer., ISBN: ISBN 978-94-017-9020-8 (eBook)
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ABSTRACT: Ten years after a threatening and previously unknown disease of oaks and tanoaks appeared in coastal California, a significant amount of progress has been made toward the understanding of its causal agent Phytophthora ramorum and of the novel pathosystems associated with this exotic organism. However, a complete understanding of the ecology and epidemiology of this species still eludes us. In part, our inability to fully understand this organism is due to its phylogenetic, phylogeographic, phenotypic, and epidemiological complexities, all reviewed in this paper. Most lines of evidence suggest that the high degree of disease severity reported in California is not simply due to a generalized lack of resistance or tolerance in naïve hosts but also to an innate ability of the pathogen to survive in unfavorable climatic conditions and to reproduce rapidly when conditions become once again favorable.Eukaryotic Cell 11/2012; 11(11). · 3.18 Impact Factor