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Downy mildews (Peronosporaceae) and White blister-rusts (Albuginaceae) of Wales
Halophytes are salt-tolerant plants growing in saline ecosystems and are spread throughout the Mediterranean area. Recently, there has been a renewed interest in agricultural exploitation of halophytes, but poor attention has been given to pest and disease management of these species. The objective of this review is to assess the extent and distribution of pathogenic fungal and fungal-like (Oomycota) organisms on major Mediterranean halophytes. We retrieved 92 references spanning over 100 years, with more than half published since 2000. Ascomycota is the best-represented phylum, and the order Pleosporales has the highest species diversity. The order Pucciniales prevails in Basidiomycota, whereas Peronosporales is the richest order within Oomycota. Most of the pathogenic species have been isolated from aboveground organs, especially from leaves. Portulaca oleracea is the species with the most associated pathogens (16) and records (28). Leveillula powdery mildew, caused by Leveillula taurica, is the most common disease among the selected species. Cakile maritima was found to be vulnerable to different mycotoxigenic Alternaria species. Strengthening the research on diseases of halophytes is essential to successfully grow these species and to evaluate the risks related to the presence of mycotoxigenic species, which is crucial for the effective exploitation of halophytes as crops.
A case is made for the counter‐intuitive proposal that plant pathologists and plant pathological societies should consider the development of policies for the conservation of plant pathogens. First the report of the Royal Botanic Gardens, Kew, entitled The State of the World’s Plants and Fungi 2020, is reviewed briefly. Next, the reasons why plant pathologists should take this report seriously are outlined and the risks to plant pathogen diversity assessed. In this section and all that follow, the paper focuses on fungal (sensu lato) pathogens, although it is suggested that the general principles developed apply to all plant pathogens, whatever their taxonomic status. There then follows an assessment of the significance of native plant pathogens in the functioning, stability and productivity of unmanaged and partially managed plant populations and communities. It is concluded that there is now compelling and growing evidence that very many do play such a role. Also assessed, more briefly, is the actual or potential value of plant pathogens to human activities, such as selecting for novel disease‐resistance factors in evolving populations of wild crop relatives, developing novel, sustainable plant disease and weed control strategies, use in industrial processes and use as model systems for research. New and evolving genomics technologies are likely to facilitate significantly the study or selection of the benefits of plant pathogens to ecosystems or human activities. Potential strategies for the conservation of plant pathogens are outlined briefly, including in situ in unmanaged and partially managed ecosystems and centres of diversity of the progenitors of crop species, and ex situ in culture, spore, DNA, and herbarium collections. In these and many other areas of plant pathology, citizen science research groups have a potentially significant role. It is concluded that there is a strong case for plant pathologists and plant pathological societies to develop and act upon strategies for the conservation and sustainable use of plant pathogens.
The smut fungi and their allies are a group of specialist plant pathogens. Eighty-one species are recorded from Wales, sixty-six on native plants. Twenty-nine species on native hosts are either considered to be extinct or threatened with extinction. Amounting to 44% of the total, the percentage lost or threatened is over twice as high as for any other studied plant or fungus group in Wales. Over 130 host/fungus interactions are recorded from the 13 Welsh Vice-counties. With little detailed long term recording to establish population trends the
threats identified stem almost exclusively from known small population sizes. Whilst superficially some might consider the extinction of parasitic species to be no great loss, the smut fungi are proving to possess useful biochemical pathways. Their selection pressure on plants may have led to the evolution of many genes for resistance that may be of value in crop protection.
The genus Hyaloperonospora (Peronosporaceae; Oomycota) is an obligate biotrophic group that causes downy mildew disease on the Brassicaceae and allied families of Brassicales, including many economically relevant crops, such as broccoli, cabbage, radish, rape, and wasabi. To investigate the diversity of Hyaloperonospora species in northeast Asia, we performed a morphological analysis for the dried herbarium specimens collected in Korea, along with molecular phylogenetic inferences based on internal transcribed spacer rDNA and cox2 mtDNA sequences. It was confirmed that 14 species of Hyaloperonospora exist in Korea. Of these, three species, previously classified under the genus Peronospora, were combined to Hyaloperonospora: H. arabidis-glabrae comb. nov. (ex Arabis glabra), H. nasturtii-montani comb. nov. (ex Rorippa indica), and H. nasturtii-palustris comb. nov. (ex Rorippa palustris). In addition, finding two potentially new species specific to northeast Asian plants is noteworthy in support of the view that the species abundance of Hyaloperonospora has been underestimated hitherto.
Leaves with typical symptoms of downy mildew were found on common agrimony in the Czech Republic in 2014 and 2015 and at several locations in Germany from 2010 to 2014. The causal agent of downy mildew of agrimony was often reported as Peronospora agrimoniae, but sometimes also as P. sparsa. Morphological characteristics of the pathogens found in both countries are in the range of previous works for P. agrimoniae, but also other downy mildews parasitic on Rosaceae, rendering their discrimination based on published observations difficult. For molecular identification sequencing of several loci (nrITS rDNA, cox1 and cox2) was performed. Phylogenetic analyses based on nrITS rDNA clearly separated P. agrimoniae from other Peronospora species infecting Rosaceae. Thus, considering P. agrimoniae as separate species seems justified. Two German specimens were identical to two Czech samples in both nrITS rDNA and cox1 mtDNA sequences, but differed in a single nucleotide substitution in cox2 region. To our knowledge, this is the first verified record of P. agrimoniae on common agrimony in the Czech Republic.
Hop downy mildew (caused by Pseudoperonospora humuli) is a yield-limiting disease in many hop-production regions of the world. In this research, 110 cultivars that are or were widely grown in the United States, Europe, or Australasia were evaluated in western Oregon over three years for their reaction to the shoot infection phase of downy mildew and vigor. There was a large range of downy mildew susceptibility and vigor amongst commercial cultivars, with some cultivars possessing a very high level of resistance. Overall, however, disease resistance and vigor were significantly greater in cultivars originating from Europe than those originating from the United States, Japan, and Australia/New Zealand. Amongst a subset of 79 cultivars, vigor was negatively correlated with levels, in cones, of cohumulone, a chemical constitute of bittering acids typically found in germplasm derived from North America. The generally poor vigor observed in cultivars derived outside of Europe likely is indicative of a lack of tolerance to the crown infection phase of the disease. Thus, the best sources of downy mildew resistance seems to be found in cultivars from the United Kingdom and continental Europe, and such cultivars are typically lower yielding and lack distinctive aroma and flavor characteristics presently desired by craft brewers. Introgression of downy mildew resistance into North American germplasm with high yield and desirable brewing characteristics is needed.
Accepted for publication 3 March 2016. Published 7 March 2016.
The genus Basidiophora (Chromista, Oomycota, Peronosporales) is revised and restricted to one species, B. entospora, with the recently described B. montana as a synonym. Basidiophora kellermanii is transferred to a new genus, Benua. The two species are described, illustrated, and their host range and distribution completed.