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: Laurens Kroon[show abstract] [hide abstract]
ABSTRACT: ABSTRACT A new devastating disease in the United States, commonly known as Sudden Oak Death, is caused by Phytophthora ramorum. This pathogen, which previously was described attacking species of Rhododendron and Viburnum in Germany and the Netherlands, has established itself in forests on the central coast of California and is killing scores of native oak trees (Lithocarpus densiflora, Quercus agrifolia, Q. kelloggii, and Q. parvula var. shrevei). The phytosanitary authorities in the European Union consider non-European isolates of P. ramorum as a threat to forest trees in Europe. To date, almost all European isolates are mating type A1 while those from California and Oregon are type A2. The occurrence of both mating types in the same region could lead to a population capable of sexual recombination, which could generate a new source of diversity. To prevent contact between these two populations, a rapid, reliable, and discriminating diagnostic test was developed to easily distinguish the two populations. Based on a DNA sequence difference in the mitochondrial Cytochrome c oxidase subunit 1 (Cox1) gene, we developed a single-nucleotide polymorphism (SNP) protocol to distinguish between isolates of P. ramorum originating in Europe and those originating in the United States. A total of 83 isolates of P. ramorum from Europe and 51 isolates from the United States were screened and all isolates could be consistently and correctly allocated to either the European or the U.S. populations using the SNP protocol.Phytopathology 07/2004; 94(6):613-20. · 2.97 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Meiosis was observed in the gametangia of A1 × A2 pairings of P. cinnamomi (n = 9 or 10), P. infestons (n = 9 or 10) and P. drechsleri (n = 9–12). Gametangial divisions in A2 isolates of the three species which were induced to self by the presence of Trichoderma were indistinguishable from those in the pairings. Counts of nuclei in selfed gametangia of P. cinnamomi confirmed that two nuclear divisions occurred. In P. infestans an association of six chromosomes indicating chromosomal structural hybridity was observed both in A1 × A2 pairings and in A2 selfed. An association of four chromosomes was observed in A1 × A2 and A2 selfed in P. drechsleri. These multiple associations provide conclusive evidence that the divisions are meiotic. Stages of fertilization were observed in P. cinnamomi and P. infestans. Differential staining indicated that both A1 and A2 oogonia were produced in the A1 × A2 pairings of P. drechsleri and also in P. cinnamomi; and that both selfed and hybrid gametangia occurred in P. cinnamomi. Single oospore cultures from A2 selfed segregated for cultural characters in P. drechsleri but no segregation for compatibility type occurred. Supporting evidence for diploidy is examined and the significance of a diploid life cycle for Phytophthora is discussed.Transactions of the British Mycological Society 01/1975; 65(1).
- [show abstract] [hide abstract]
ABSTRACT: Co-existence of both mating types A1 and A2 within the EU1 lineage of Phytophthora ramorum has only been observed in Belgium, which begs the question whether sexual reproduction is occurring. A collection of 411 Belgian P. ramorum isolates was established during a 7-year survey. Our main objectives were genetic characterization of this population to test for sexual reproduction, determination of population structure, evolution and spread, and evaluation of the effectiveness and impact of control measures. Novel, polymorphic simple sequence repeat (SSR) markers were developed after screening 149 candidate loci. Eighty isolates of P. ramorum, broadly representing the Belgian population, were analyzed using four previously described and three newly identified polymorphic microsatellite loci as well as amplified fragment length polymorphisms. SSR analysis was most informative and was used to screen the entire Belgian population. Thirty multilocus genotypes were identified, but 68% of the isolates belonged to the main genotype EU1MG1. Although accumulated mutation events were detected, the overall level of genetic diversity within the Belgian isolates of P. ramorum appears to be limited, indicating a relatively recent clonal expansion. Based on our SSR analysis there is no evidence of sexual recombination in the Belgian population of P. ramorum. Metalaxyl use decreased the genetic diversity of P. ramorum until 2005, when the majority of the isolates had become resistant. Most genotypes were site-specific and despite systematic removal of symptomatic and neighbouring plants, some genotypes were detected over a period of several years at a single site, sometimes discontinuously, indicating (latent) survival of the pathogen at those sites.Molecular Ecology 11/2009; 19(1):92-107. · 6.28 Impact Factor