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Botanical gardens have extensive spatial databases of their plant specimens; however, the fungi occurring in them are generally unstudied. Botanical gardens, with their great plant diversity, undoubtedly harbor a wide range of symbiotic fungi, including those that are plant-pathogenic. One such group of fungi is powdery mildews (Erysiphaceae). The powdery mildews are among the most prevalent and economically important plant pathogens in the world, with an estimated 906 species in 19 genera. They are known to infect more than 10,000 species of flowering plants and although some species occur across a range of hosts, many are associated with specific plants. Powdery mildews have undergone a long and dynamic coevolution with their host plants, resulting in co-speciation. Botanical gardens provide a living laboratory in which to study these fungi, leading to a wealth of undiscovered fungal diversity. Furthermore, monitoring pathogens in botanical gardens has led to important ecological findings related to the plant sciences and plant protection. Between 2018 and 2022, a collaborative citizen science project was established with 10 botanical gardens in the United States and Mexico. A total of more than 300 powdery mildew specimens were collected on 220 different host taxa. We sequenced the entire internal transcribed spacer (ITS) and large subunit (LSU) rDNA loci and phylogenetically and morphologically analyzed these collections revealing 130 species, of which 31 are likely unknown to science. This research highlights the importance of botanical gardens as a reservoir of fungal diversity. Future research will further elucidate the coevolutionary relationship between powdery mildews and their hosts and extend the current study to evaluate other plant pathogens and fungi in botanical gardens. [ABSTRACT FROM AUTHOR]

Phylogenetic and morphological analyses have been conducted on powdery mildew specimens on different Berberis and Mahonia spp. from Asia, Europe and North America. The present study showed that collections of Erysiphe berberidis exhibit a high degree of morphological plasticity of the sexual morph, in contrast to their morphologically, rather uniform, asexual morph. In phylogenetic tree, all sequences cluster in a large strongly supported clade, without any indication and support for further differentiation into cryptic species. There are three morphological types within E. berberidis s. lat. that contain consistent differences. Until future multi-locus analyses will be available, we prefer to treat these 'morphological types' as varieties. These include Erysiphe berberidis var. berberidis, E. berberidis var. asiatica, and E. berberidis var. dimorpha comb. nov. (≡ Microsphaera berberidis var. dimorpha, M. berberidicola, and M. multappendicis). To fix the application of species name E. berberidis, an appropriate epitype was designated, with an ITS sequences. [ABSTRACT FROM AUTHOR]

Powdery mildew on oak, caused by Erysiphe spp., has been shown to have serious ecological consequences on a range of Quercus hosts. Erysiphe alphitoides and E. quercicola are two of the most heavily studied and common powdery mildews known to occur on Quercus species. In recent years, these species have been noted throughout the world on a range of hosts within and outside the Quercus genus. Reports that E. alphitoides was absent in European herbaria before 1921 and the discovery of the holotype of E. alphitoides from 1911 in an American herbarium (FH) led to the current study in which we genetically analysed six specimens of E. alphitoides s. lat including, most importantly, the holotype of E. alphitoides from France collected in 1911. The results of our analyses revealed that: (1) The sequence of the E. alphitoides holotype falls within the E. quercicola clade, confirming that E. alphitoides did not spread to Europe until ~1921. (2) E. alphitoides var. chenii forms a monophyletic clade with E. epigena and should be reduced to synonymy with that species and (3) through sequence analyses E. alphitoides and E. quercicola are confirmed to have spread to North America. The sequencing results of the E. alphitoides holotype have severe nomenclatural‐taxonomic consequences. A proposal was submitted simultaneously with the present manuscript to conserve the name E. alphitoides so that the traditional usage of the names E. alphitoides and E. quercicola could be maintained. The sequences obtained for the current study provide new insight into the taxonomy and spread of these ecologically significant, globally distributed species. The present study highlights the importance of sequencing specimens from type material, above all when morphological similar species are involved. [ABSTRACT FROM AUTHOR]

The phylogeny and taxonomy of Podosphaera filipendulae (including P. filipendulensis, syn. nov.) have been examined. Asian, European and North American collections were examined and the nucleotides sequences of their partial rDNA region were determined. In particular, the relationship between P. filipendulae and P. spiraeae was analysed. The results confirmed P. filipendulae and P. spiraeae as two separate, morphologically similar species. The phylogenetic analysis revealed a similar phylogeny to that of the host genera. Although ITS sequences retrieved from Asian, European and North American specimens of P. filipendulae on various Filipendula spp. are identical to sequences from P. macularis on hop, there is consistently one base substitution at the 5'-end of 28S rRNA gene between the species. This result provides evidence that the hop powdery mildew and P. filipendulae are biologically and morphologically clearly distinguished, and should be maintained as two separate species. [ABSTRACT FROM AUTHOR]

The introduction, spread, and impact of fungal plant pathogens is a critical concern in ecological systems. In this study, we were motivated by the rather sudden appearance of A cer macrophyllum heavily infected with powdery mildew. We used morphological and genetic analyses to confirm the pathogen causing the epidemic was Sawadaea bicornis. In subsequent field studies, this pathogen was found in several locations in western North America, and in greenhouse studies, A. macrophyllum was found to be significantly more susceptible to S. bicornis than nine other Acer species tested. A genetic analysis of 178 specimens of powdery mildew from freshly collected and old herbarium specimens from 15 countries revealed seven different haplotypes. The high diversity of haplotypes found in Europe coupled with sequence results from a specimen from 1864 provides evidence that S. bicornis has a European origin. Furthermore, sequence data from a specimen from 1938 in Canada show that the pathogen has been present in North America for at least 82 years revealing a considerable lag time between the introduction and current epidemic. This study used old herbarium specimens to genetically hypothesize the origin, the native host, and the invasion time of a detrimental fungal plant pathogen. • We observed a powdery mildew epidemic on Acer macrophyllum in Seattle WA. • We subsequently identified the powdery mildew species as Sawadaea bicornis. • Acer macrophyllum is significantly more susceptible to S. bicornis than nine other Acer species tested. • We identified 7 S. bicornis haplotypes from sequence data acquired from fresh and herbarium specimens collected throughout the world. • Based on multiple lines of evidence we contend that this pathogen has a European origin. [ABSTRACT FROM AUTHOR]

Erysiphe species (powdery mildews) on Corylus and Ostrya hosts (Betulaceae subfam. Coryloideae) in Asia and North America are widespread pathogens on these economically and ecologically valuable nut crops. An improved understanding of their phylogeny and taxonomy is of ecological and applied importance. Phylogenetic analyses and morphological reexaminations conducted in this study revealed a higher degree of diversity and cryptic speciation than reflected in earlier species concepts. North American collections on C. cornuta, which were previously assigned to E. corylacearum, proved to constitute a species of its own and are herein introduced as E. cornutae, sp. nov. Two additional North American species, E. coryli-americanae, sp. nov. and E. ostryae, sp. nov., have been detected on C. americana and O. virginiana and are described. They are morphologically similar to E. cornutae, but genetically distinct. Based on phylogenetic analyses, E. corylacearum is an Asian species confined to various Asian Corylus species. Sequence data retrieved from Japanese type material of E. corylicola revealed that this species clusters with sequences from E. elevata on Catalpa species, distant from all other Erysiphe species on Corylus. Morphologically similar, yet distinct, specimens on C. sieboldiana, which were previously assigned to E. corylicola, form a distinct, distant clade. The species involved is described herein as E. pseudocorylacearum, sp. nov. Additionally, an unusual infection of C. sieboldiana in Japan by E. syringae has been shown by means of sequence data. The phylogeny and taxonomy of Erysiphe species belonging to the Corylioideae are discussed in detail, and a key to the species concerned is provided. [ABSTRACT FROM AUTHOR]

Powdery mildew is a detrimental foliar disease of sweet cherry trees. The disease is predominantly managed by spraying synthetic fungicides throughout the growing season. The emergence of resistant powdery mildew populations, to some commonly used synthetic fungicides, highlights the need for research into alternative control methods. Between 2012 and 2015, the efficacy of two different biofungicides (Bacillus subtilis and Bacillus pumilus) and electrolysed oxidised (EO) water were evaluated to determine if they could be a viable replacement for four commonly used synthetic fungicides (fluopyram/trifloxystrobin, triflumizole, quinoxyfen and myclobutanil) in a greenhouse, nursery and commercial orchard. Electrolysed oxidised water and fluopyram/trifloxystrobin significantly lowered disease severity and incidence in all of the locations tested, however, biweekly applications of EO water had little effect on the fungus and weekly applications were phytotoxic in the nursery and greenhouse. Before EO water is implemented into integrated pest management programmes, the optimal spray frequency needs to be evaluated to eliminate its phytotoxic effects. The biofungicides evaluated in this study had minimal effects on powdery mildew severity and incidence and should not be recommended for control on sweet cherry trees. Currently, synthetic fungicides are the best method for the control of powdery mildew as fluopyram/trifloxystrobin was the only fungicide that was successful in lowering disease incidence and severity over the duration of the powdery mildew epidemic in both the nursery and greenhouse. Future research should evaluate integrated pest management strategies, including additional biofungicides, that could supplement and reduce synthetic fungicide applications. [ABSTRACT FROM AUTHOR]