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Over the past few years, symptoms akin to late blight disease have been reported on a variety of crop plants in South America. Despite the economic importance of these crops, the causal agents of the diseases belonging to the genus Phytophthora have not been completely characterized. In this study, a new Phytophthora species was described in Colombia from tree tomato (Solanum betaceum), a semi-domesticated fruit grown in northern South America. Comprehensive phylogenetic, morphological, population genetic analyses, and infection assays to characterize this new species, were conducted. All data support the description of the new species, Phytophthora betacei sp. nov. Phylogenetic analyses suggest that this new species belongs to clade 1c of the genus Phytophthora and is a close relative of the potato late blight pathogen, P. infestans. Furthermore, it appeared as the sister group of the P. andina strains collected from wild Solanaceae (clonal lineage EC-2). Analyses of morphological and physiological characters as well as host specificity showed high support for the differentiation of these species. Based on these results, a complete description of the new species is provided and the species boundaries withinPhytophthora clade 1c in northern South America are discussed.

Oomycetes form a deep lineage of eukaryotic organisms that includes a large number of plant pathogens that threaten natural and managed ecosystems. We undertook a survey to query the community for their ranking of plant pathogenic oomycete species based on scientific and economic importance. In total, we received 263 votes from 62 scientists in 15 countries for a total of 33 species. The Top 10 species and their ranking are: (1) Phytophthora infestans; (2, tied) Hyaloperonospora arabidopsidis; (2, tied) Phytophthora ramorum; (4) Phytophthora sojae; (5) Phytophthora capsici; (6) Plasmopara viticola; (7) Phytophthora cinnamomi; (8, tied) Phytophthora parasitica; (8, tied) Pythium ultimum; and (10) Albugo candida. The article provides an introduction to these 10 taxa and a snapshot of current research. We hope that the list will serve as a benchmark for future trends in oomycete research.

Limited knowledge is available on Phytophthora infestans populations in Sub-Saharan Africa (SSA). Therefore, and in response to recent severe late blight epidemics, P. infestans isolates from potato, tomato and Petunia×hybrida from eight SSA countries w

The oomycete pseudofungus Phytophthora infestans (Mont.) de Bary, the causal organism of late blight, is considered to be one of the most devastating pathogens affecting potatoes and tomatoes worldwide. In Europe, the pathogen caused severe epidemics on potatoes after its introduction in 1845. Late blight management became much more troublesome after the introduction of another P. infestans population of Mexican origin. The present population of P. infestans in the Netherlands and an increasing number of other European countries consists of both A1 and A2 mating type isolates and sexual reproduction has been reported. The goals of this thesis were to study late blight epidemiology and population biology of the present P. infestans population. Therefore, sources and patterns of variation for pathogenicity in sexual P. infestans populations were studied and the impact of increased levels of aggressiveness on the stability of partial resistance to late blight was investigated. Results showed that considerable levels of variation for aggressiveness are maintained in regional populations of P. infestans in the Netherlands and that oospores are readily produced in field crops and volunteer potato plants. Oospore production and viability proved to be highly dependent on combining abilities of parental strains and there are indications that oospores are able to survive in soils for three to four years. Increased aggressiveness and cultivar-by-isolate interactions between partial resistant potato cultivars and P. infestans strains negatively affect the stability of resistance. Population genetic studies in its centre of origin and diversity revealed differentiation within the Toluca Valley implying host specificity. From the results presented in this thesis, it is clear that the introduction of a sexually reproducing population of P. infestans in the Netherlands has had a major impact on late blight epidemics and population biology of the late blight pathogen. Sexual reprodu