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.
- SourceAvailable from: Lien Bertier[Show abstract] [Hide abstract]
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
- [Show abstract] [Hide abstract]
ABSTRACT: All Phytophthora ramorum EU1 lineage isolates tested are of A1 mating type, except for three rare isolates from 2002 to 2003 from Belgium, which were originally assigned the A2 mating type. In one of these isolates (2338), a switch from A2 to A1 mating type was observed in 2006. This observation initiated a larger study in which all cultures and subcultures of the original three EU1 A2 isolates, maintained in three laboratories under different storage conditions, were checked for mating type change. The A2 to A1 mating type switch was observed in four of seven independently maintained isolates that were derived from isolate 2338 in two laboratories, using different transfer regimes and storage conditions. Following the mating type switch to A1 in these four derived isolates, no reversion back to A2 mating was observed, even after up to 5 years of additional isolate maintenance and several more subculturing events. The three other isolates that were derived from isolate 2338 as well as the other EU1 A2 isolates collected in 2002 and 2003 and stored in the same conditions did not display such mating type change. The potential causes of the mating type conversions as well as their epidemiological implications are discussed.Journal of Phytopathology 01/2014; 162(1). · 1.00 Impact Factor
- [Show abstract] [Hide abstract]
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