Phytophthora

Development of a Toolbox to Study Phytophthora cryptogea-Lettuce Interactions: Characterization and Detection of P. cryptogea in Hydroponic Lettuce

Climate change poses a major threat to crop production, resulting in the emergence of new pests and diseases. Phytophthora cryptogea has recently emerged as a major concern in hydroponic lettuce cultivation, causing substantial yield and economic losses. This oomycete pathogen thrives in elevated water temperatures induced by warmer weather conditions (e.g., heatwaves), facilitating rapid pathogen propagation. Although the disease is already present for several decades in chicory cultivation, where it originates from the field, its origin in lettuce cultivation remains unclear. To get a better understanding of its origin, we conducted a multilocus sequence analysis using five reference genes (ITS, β-tub, COI, EF1α, and HSP90) and 33 P. cryptogea isolates from various hosts, including chicory and lettuce. Results revealed a clear separation between lettuce and chicory isolates. Furthermore, we developed and implemented a robust disease bioassay and qPCR assay to investigate the interaction between P. cryptogea strains and lettuce. Our findings revealed that while lettuce isolates exhibited the highest virulence, some chicory isolates also caused disease in lettuce, suggesting a potential evolutionary link between P. cryptogea in lettuce and chicory. Our experiments also revealed that even a low concentration of zoospores (100 zoospores/liter) can elicit severe symptoms, underscoring the pathogen's high virulence. Therefore, effective disease management strategies are needed for controlling (the spread of) the disease. Together, this research provides several tools that can be used to enhance our understanding of the interaction between P. cryptogea and its host plants, including the development of proper disease management strategies.

Oomycete Diversity and Ecology in Declining Alder Stands in Switzerland

In this study, we assessed the occurrence and diversity of four oomycete genera (Phytophthora, Phytopythium, Pythium, and Globisporangium) in 13 declining alder (Alnus glutinosa and A. incana) stands in Switzerland. For this, we sampled and analyzed soil from tree rhizosphere, water from streams and rivers along which the stands were located, and symptomatic alder bark. The overall isolation rate was 47.2%, with a total of 400 oomycete isolates recovered at all 13 sites. The highest incidence of oomycete isolates was in soil samples (baiting, 82.5% isolation rate), followed by water (baiting, 14.7%), and bark (direct isolation, 2.7%). Of all recovered oomycete isolates, 90.3% could be successfully assigned to a known species, for a total of 23 species identified, including both preferential saprotrophs and pathogens. Among all genera, Phytophthora was the most abundant with 273 isolates (75.6%), followed by Phytopythium, Pythium, and Globisporangium. Oomycete species diversity showed a significant variation among substrates. Only one species-Phytophthora lacustris-was abundant in all substrates, while 16 species were restricted to a specific substrate, mainly soil. The rhizosphere of symptomatic alder trees harbored the most diverse oomycete community, highlighting once again the importance of soil as a reservoir for these microorganisms. Only two Phytophthora species were isolated from alder bark lesions, namely, P. × alni, the known causal agent of alder decline, and P. lacustris. The low recovery rate of P. × alni might be due to attempts to isolate it from old, inactive lesions, but may also suggest that alder decline might be caused by other oomycetes infecting the root system of the trees.

Phytophthora inundata: A New Root Pathogen of Citrus in Europe and the Mediterranean Region

Citruses are one of the major fruit crops globally. Among Mediterranean citrus producers, Sicily (southern Italy) is renowned for its high-quality fresh fruit production. Phytophthora diseases are a serious issue for citrus production worldwide and Phytophthora nicotianae is a prevalent causal agent of root rot in most citrus growing areas globally and particularly in the Mediterranean region. This study reports the occurrence of Phytophthora inundata as a root pathogen of declining mature citrus trees in eastern Sicily in association with P. nicotianae. This is the first record of P. inundata on citrus in Europe and the Mediterranean region. The species was identified on the basis of a morphology and multi-gene phylogenetic analysis, which included the internal transcribed spacer, β-tubulin and cytochrome c oxidase subunit 1. Pathogenicity tests on citrus saplings showed P. inundata was a less aggressive pathogen than P. nicotianae. However, the co-inoculation of both species produced more severe symptoms than inoculation with a single species, indicating an additive effect of these two pathogens and suggesting that opportunistic secondary pathogens like P. inundata may have a crucial role in complex diseases.

A qPCR assay for the detection of Phytophthora abietivora, an emerging pathogen on fir species cultivated as Christmas trees

Emerging species of the Phytophthora genus are among the most important threats to global plant biodiversity, horticulture and trade. For instance, Phytophthora root rot (PRR) of Christmas trees, mainly Fraser (Abies fraseri) and balsam (Abies balsamea) firs, is responsible for an average of 10% of the observed diseased trees in plantations. Diagnosing PRR involves isolation followed by morphological and molecular identification of the causal agents. However, these methods are rarely adapted to larger scale monitoring such as in situ detection. For these applications, molecular detection of environmental DNA (eDNA) provides the fast and high-throughput results needed. Phytophthora abietivora was associated with PRR in firs (Abies spp.) cultivated as Christmas trees in the province of Québec (Canada). This study focused on developing a sensitive and specific qPCR assay targeting P. abietivora and validating its efficiency on DNA extracted from soil and roots. A set of primers and probe was designed for this assay, and parameters such as the limit of detection (LOD95%) and limit of quantification (LOQ) were measured. The assay was tested on DNA obtained from healthy-looking and PRR symptomatic Fraser and balsam firs. The assay was shown to be semi-specific because it cross-reacted with P. europaea and three other phylogenetically close species, but deemed specific in the context of PRR of firs. The LOD95% was estimated at 10 copies per reaction (Cq of 35.7) and the LOQ to 33 P. abietivora oospores per gram of soil. Out of 488 DNA samples from soil, 68 were positive for P. abietivora from which 42 (61.7%) were from PRR symptomatic trees. Only a slight overlap (3 out of 7 samples) was observed with previously obtained baiting results. This assay will be useful for rapid diagnostics of P. abietivora infected trees and as a prospecting tool to better characterize the natural distribution and dissemination of the disease.

Evolutionary Relationships of the Phytophthora 1a Subclade Species Based on Complete Mitogenomes, and Novel Markers for Their Differentiation

Phytophthora is a genus of oomycetes that includes many aggressive pathogens capable of devastating farmlands and forests worldwide. Among the oldest and most well-known species, P. cactorum exhibits morphological and genetic similarities to other homothallic species within subclade 1a, which complicates the understanding of their evolutionary relationships. This study primarily compared seven P. cactorum strains from diverse origins with three closely related species in subclade 1a, utilizing mitogenome sequences for analysis. The circular mitogenomes of the four species were nearly identical in size and comprised 38 protein-coding genes (PCGs), 25 transfer ribonucleic acid genes, and 2 ribosomal RNA genes. The mitochondrial genomes exhibited a higher percentage of A/T compared to G/C content. The majority of AT-skew and GC-skew values among the 38 PCGs were positive, with the AT-skew demonstrating a more pronounced bias than the GC-skew. The Ka/Ks ratios revealed that 35 PCGs underwent significant purifying selection. Although the AliGROOVE analysis indicated notable similarities among the subclade 1a species, four PCGs exhibited significantly higher pairing frequency compared to the complete mitogenome. The results from the phylogenetic analysis aligned with the pairwise genetic distances, indicating that P. cactorum is more closely related to P. pseudotsugae than to P. hedraiandra. Furthermore, we found that the nad9 gene is informative to differentiate closely related Phytophthora species within subclade 1a, akin to the cox1 gene.

Transient expression of fluorescent proteins and Cas nucleases in Phytophthora agathidicida via PEG-mediated protoplast transformation

Phytophthora species are eukaryotic plant pathogens that cause root rot and dieback diseases in thousands of plant species worldwide. Despite their significant economic and ecological impacts, fundamental molecular tools such as DNA transformation methods are not yet established for many Phytophthora species. In this study, we have established a PEG/calcium chloride (CaCl2)-mediated protoplast transformation method for Phytophthora agathidicida, the causal agent of kauri dieback disease. Adapting a protocol from Phytophthora sojae, we systematically optimized the protoplast digesting enzymes, recovery media composition and pH. Our findings reveal that chitinases are essential for P. agathidicida protoplast formation, and the optimum pH of the recovery medium is 5. The media type did not significantly impact protoplast regeneration. Using this protocol, we generated transformants using three plasmids (i.e. pTdTomatoN, pYF2-PsNLS-Cas9-GFP and pYF2-PsNLS-Cas12a-GFP), which expressed fluorescent proteins and/or Cas nucleases. The transformants were unstable unless maintained under antibiotic selective pressure; however, under selection, fluorescence was maintained across multiple generations and life cycle stages, including the production of fluorescent zoospores from transformed mycelia. Notably, we observed the expression of GFP-tagged Cas nucleases, which is promising for future CRISPR-Cas genome editing applications. This study demonstrates that P. agathidicida is amenable to PEG/CaCl2-mediated protoplast transformation. Although the resulting transformants require antibiotic selective pressure to remain stable, this transient expression system can be valuable for applications such as cell tracking, chemotaxis studies and CRISPR-Cas genome editing. The protocol also provides a foundation for further optimization of transformation methods. It serves as a valuable tool for exploring the molecular biology of P. agathidicida and potentially other closely related Phytophthora species.

The Heterogeneity of Ornamental Plants in Nurseries Increases the Chance of Finding New Hosts for Phytophthora

The production of ornamental plants in Mexico represents a job-generating activity that has grown in recent years; however, it is adversely affected by phytosanitary issues, notably those induced by Phytophthora. Studies of Phytophthora in ornamental nurseries are scarce in Mexico. The aim in this study was to identify Phytophthora species from selected ornamental plant nurseries in Mexico as potential new hosts. Samples of 13 genera diseased plant tissue and soil were collected from eight nurseries in Mexico during 2009-2010. Based on morphology and sequences of ITS rDNA, the 19 isolates obtained were identified as P. cactorum, P. capsici, P. cinnamomi, P. drechsleri, P. kelmanii, P. nicotianae, and P. tropicalis. Additional loci were sequenced to support species determinations within the P. capsici species complex; some of these isolates could not be confirmed as belonging to any described species, and one appeared to be an interspecific hybrid. This is the first report of P. kelmanii in Mexico; this is noteworthy due to being a broad host range, similar to most of the other species encountered. Evidence of nursery-grown plants serving as a Phytophthora vector to a home garden has been reported for the first time in Mexico. Cestrum nocturnum and Solanum ovigerum are new hosts for Phytophthora worldwide.

A pangenome analysis reveals the center of origin and evolutionary history of Phytophthora infestans and 1c clade species

We examined the evolutionary history of Phytophthora infestans and its close relatives in the 1c clade. We used whole genome sequence data from 69 isolates of Phytophthora species in the 1c clade and conducted a range of genomic analyses including nucleotide diversity evaluation, maximum likelihood trees, network assessment, time to most recent common ancestor and migration analysis. We consistently identified distinct and later divergence of the two Mexican Phytophthora species, P. mirabilis and P. ipomoeae, from P. infestans and other 1c clade species. Phytophthora infestans exhibited more recent divergence from other 1c clade species of Phytophthora from South America, P. andina and P. betacei. Speciation in the 1c clade and evolution of P. infestans occurred in the Andes. P. andina-P. betacei-P. infestans formed a species complex with indistinct species boundaries, hybridizations between the species, and short times to common ancestry. Furthermore, the distinction between modern Mexican and South American P. infestans proved less discrete, suggesting gene flow between populations over time. Admixture analysis indicated a complex relationship among these populations, hinting at potential gene flow across these regions. Historic P. infestans, collected from 1845-1889, were the first to diverge from all other P. infestans populations. Modern South American populations diverged next followed by Mexican populations which showed later ancestry. Both populations were derived from historic P. infestans. Based on the time of divergence of P. infestans from its closest relatives, P. andina and P. betacei in the Andean region, we consider the Andes to be the center of origin of P. infestans, with modern globalization contributing to admixture between P. infestans populations today from Mexico, the Andes and Europe.

The Good, the Bad, and the Fungus: Insights into the Relationship Between Plants, Fungi, and Oomycetes in Hydroponics

Hydroponic systems are examples of controlled environment agriculture (CEA) and present a promising alternative to traditional farming methods by increasing productivity, profitability, and sustainability. In hydroponic systems, crops are grown in the absence of soil and thus lack the native soil microbial community. This review focuses on fungi and oomycetes, both beneficial and pathogenic, that can colonize crops and persist in hydroponic systems. The symptomatology and mechanisms of pathogenesis for Botrytis, Colletotrichum, Fulvia, Fusarium, Phytophthora, Pythium, and Sclerotinia are explored for phytopathogenic fungi that target floral organs, leaves, roots, and vasculature of economically important hydroponic crops. Additionally, this review thoroughly explores the use of plant growth-promoting fungi (PGPF) to combat phytopathogens and increase hydroponic crop productivity; details of PGP strategies and mechanisms are discussed. The benefits of Aspergillus, Penicillium, Taloromyces, and Trichoderma to hydroponics systems are explored in detail. The culmination of these areas of research serves to improve the current understanding of the role of beneficial and pathogenic fungi, specifically in the hydroponic microbiome.

Full-Length ITS Amplicon Sequencing Resolves Phytophthora Species in Surface Waters Used for Orchard Irrigation in California's San Joaquin Valley

Diverse Phytophthora species, including many important plant pathogens, have been widely detected among surface water irrigation sources. In the past decade, metabarcoding has been used to characterize waterborne Phytophthora populations. Metabarcoding typically involves amplification of portions of the nuclear ribosomal internal transcribed spacers (ITSs) ITS1 or ITS2 from Phytophthora species, followed by indexed high-throughput sequencing. However, full-length sequences of the entire ITS region are required for resolution of many Phytophthora species. We used metabarcoding with Pacific Biosciences (PacBio) sequencing of full-length ITS amplicons to analyze populations of Phytophthora in waterways of the Stockton East Water District (SEWD) in the northern San Joaquin Valley of California. This approach yielded species-level resolution of many members of the Phytophthora community. Results were compared with those obtained by using ITS1 or ITS2 regions alone and were found to provide superior species resolution for P. pini, P. capsici, and P. gregata. Samples were collected throughout the 2021 irrigation season from five waterways across the SEWD. Thirty-eight Phytophthora species were detected in the waterways, including tree-crop pathogens P. acerina, P. cactorum, P. pini, P. × cambivora, P. niederhauserii, P. mediterranea, and P. taxon walnut. These pathogenic species were detected throughout the SEWD during most of the irrigation season. The results demonstrated the usefulness of full-length ITS amplicon sequencing for identifying Phytophthora species in environmental samples and suggested that some disease risk may be incurred by orchardists irrigating with SEWD water. Additional epidemiological studies will be required to critically evaluate this risk.

Cultivable root endophytic fungi associated with Acrocomia aculeata and its antagonistic activity against phytopathogenic oomycetes

Macaw palm (Acrocomia aculeata Jacq.) is a palm, native to Brazilian territory that stands out due to the amount of oil produced with applications in the biodiesel industry, cosmetics, and food. Its commercial exploitation in Brazil, including phytosanitary management is based on concepts and practices of regenerative agriculture, which has the responsibility of sustainable cultivation by avoiding, for example, the use of chemical pesticides. Recently, root and stem rot disease were reported in macaw palm seedlings caused by Phytophthora palmivora. Managing this plant pathogen is complex, and the chemical control of this soil-borne oomycete is not viable, in addition to the negative impact on the environment. Many microorganisms are studied and used as biological control agents (BCAs) against pathogens, among them the community of endophytic fungi associated with plants. This is a sustainable biotechnological alternative for plant disease control. The community of cultivable endophytic fungi associated with healthy roots of macaw palm was explored using the extinction cultivation technique and a screening was carried out to select potential antagonists against oomycetes through the dual culture test. Specific gene regions from the best isolates were amplified for identification. A total of 250 isolates were obtained, and 46 were selected for in vitro tests against representatives of phytopathogenic oomycetes. After tests against Phytophthora heterospora, Phytophthora palmivora, Pythium aphanidermatum, and Pythium deliense, two isolates were selected as potential antagonists. The phylogenetic analysis of selected isolates showed that they belong to two different species: Talaromyces sayulitensis COAD 3605 and Epicoccum italicum COAD 3608. The percentage of inhibition of phytopathogenic oomycetes testedwas until 82% in the antagonism tests conducted. From the 46 isolates selected, only 2 were selected which showed great antagonistic activity towards all oomycetes tested. These fungi will be used in upcoming studies that aim to determine the effectiveness of endophytes in controlling diseases caused by oomycetes in the field.

What are the 100 most cited fungal genera?

The global diversity of fungi has been estimated between 2 to 11 million species, of which only about 155 000 have been named. Most fungi are invisible to the unaided eye, but they represent a major component of biodiversity on our planet, and play essential ecological roles, supporting life as we know it. Although approximately 20 000 fungal genera are presently recognised, the ecology of most remains undetermined. Despite all this diversity, the mycological community actively researches some fungal genera more commonly than others. This poses an interesting question: why have some fungal genera impacted mycology and related fields more than others? To address this issue, we conducted a bibliometric analysis to identify the top 100 most cited fungal genera. A thorough database search of the Web of Science, Google Scholar, and PubMed was performed to establish which genera are most cited. The most cited 10 genera are Saccharomyces, Candida, Aspergillus, Fusarium, Penicillium, Trichoderma, Botrytis, Pichia, Cryptococcus and Alternaria. Case studies are presented for the 100 most cited genera with general background, notes on their ecology and economic significance and important research advances. This paper provides a historic overview of scientific research of these genera and the prospect for further research. Citation: Bhunjun CS, Chen YJ, Phukhamsakda C, Boekhout T, Groenewald JZ, McKenzie EHC, Francisco EC, Frisvad JC, Groenewald M, Hurdeal VG, Luangsa-ard J, Perrone G, Visagie CM, Bai FY, Błaszkowski J, Braun U, de Souza FA, de Queiroz MB, Dutta AK, Gonkhom D, Goto BT, Guarnaccia V, Hagen F, Houbraken J, Lachance MA, Li JJ, Luo KY, Magurno F, Mongkolsamrit S, Robert V, Roy N, Tibpromma S, Wanasinghe DN, Wang DQ, Wei DP, Zhao CL, Aiphuk W, Ajayi-Oyetunde O, Arantes TD, Araujo JC, Begerow D, Bakhshi M, Barbosa RN, Behrens FH, Bensch K, Bezerra JDP, Bilański P, Bradley CA, Bubner B, Burgess TI, Buyck B, Čadež N, Cai L, Calaça FJS, Campbell LJ, Chaverri P, Chen YY, Chethana KWT, Coetzee B, Costa MM, Chen Q, Custódio FA, Dai YC, Damm U, de Azevedo Santiago ALCM, De Miccolis Angelini RM, Dijksterhuis J, Dissanayake AJ, Doilom M, Dong W, Alvarez-Duarte E, Fischer M, Gajanayake AJ, Gené J, Gomdola D, Gomes AAM, Hausner G, He MQ, Hou L, Iturrieta-González I, Jami F, Jankowiak R, Jayawardena RS, Kandemir H, Kiss L, Kobmoo N, Kowalski T, Landi L, Lin CG, Liu JK, Liu XB, Loizides M, Luangharn T, Maharachchikumbura SSN, Makhathini Mkhwanazi GJ, Manawasinghe IS, Marin-Felix Y, McTaggart AR, Moreau PA, Morozova OV, Mostert L, Osiewacz HD, Pem D, Phookamsak R, Pollastro S, Pordel A, Poyntner C, Phillips AJL, Phonemany M, Promputtha I, Rathnayaka AR, Rodrigues AM, Romanazzi G, Rothmann L, Salgado-Salazar C, Sandoval-Denis M, Saupe SJ, Scholler M, Scott P, Shivas RG, Silar P, Souza-Motta CM, Silva-Filho AGS, Spies CFJ, Stchigel AM, Sterflinger K, Summerbell RC, Svetasheva TY, Takamatsu S, Theelen B, Theodoro RC, Thines M, Thongklang N, Torres R, Turchetti B, van den Brule T, Wang XW, Wartchow F, Welti S, Wijesinghe SN, Wu F, Xu R, Yang ZL, Yilmaz N, Yurkov A, Zhao L, Zhao RL, Zhou N, Hyde KD, Crous PW (2024). What are the 100 most cited fungal genera? Studies in Mycology 108: 1-411. doi: 10.3114/sim.2024.108.01.

Histone (de)acetylation in epigenetic regulation of Phytophthora pathobiology

Phytophthora species are oomycetes that have evolved a broad spectrum of biological processes and improved strategies to cope with host and environmental challenges. A growing body of evidence indicates that the high pathogen plasticity is based on epigenetic regulation of gene expression linked to Phytophthora's rapid adjustment to endogenous cues and various stresses. As 5mC DNA methylation has not yet been identified in Phytophthora, the reversible processes of acetylation/deacetylation of histone proteins seem to play a pivotal role in the epigenetic control of gene expression in oomycetes. To explore this issue, we review the structure, diversity, and phylogeny of histone acetyltransferases (HATs) and histone deacetylases (HDACs) in six plant-damaging Phytophthora species: P. capsici, P. cinnamomi, P. infestans, P. parasitica, P. ramorum, and P. sojae. To further integrate and improve our understanding of the phylogenetic classification, evolutionary relationship, and functional characteristics, we supplement this review with a comprehensive view of HATs and HDACs using recent genome- and proteome-level databases. Finally, the potential functional role of transcriptional reprogramming mediated by epigenetic changes during Phytophthora species saprophytic and parasitic phases under nitro-oxidative stress is also briefly discussed.

Pythium banihashemianum sp. nov. and Globisporangium izadpanahii sp. nov.: Two New Oomycete Species from Rice Paddies in Iran

An investigation into oomycete diversity in rice paddies of Fars Province in Iran led to the identification of two new Pythium sensu lato (s.l.) species as Globisporangium izadpanahii sp. nov. and Pythium banihashemianum sp. nov. The identification was based on morphological and physiological features as well as on the phylogenetic analysis of nuclear (ITS and βtub) and mitochondrial (cox1 and cox2) loci using Bayesian inference and Maximum Likelihood. The present paper formally describes these two new species and defines their phylogenetic relationships with other congeneric species. According to multiple gene genealogy analysis, G. izadpanahii sp. nov. was grouped with other species of Globisporangium (formerly, clade G of Pythium s.l.) and was closely related to both G. nagaii and the recently described G. coniferarum. The second species, designated P. banihashemianum sp. nov., was grouped with other species of Pythium sensu stricto (formerly, clade B of Pythium s.l.) and, according to the phylogenetic analysis, shared an ancestor with P. plurisporium. The production of globose hyphal swellings was a major characteristic of G. izadpanahii sp. nov., which did not produce vesicles and zoospores. In pathogenicity tests on rice seedlings, P. banihashemianum sp. nov. isolates were highly pathogenic and caused severe root and crown rot, while G. izadpanahii sp. nov. isolates were not pathogenic.

Survey of Phytophthora Diversity Reveals P. abietivora as a Potential Phytophthora Root Rot Pathogen in Québec Christmas Tree Plantations

Christmas trees are an economically and culturally important ornamental plant in North America. Many microorganisms are pathogens of firs cultivated as Christmas trees. Among those, Phytophthora causes millions of dollars in damage to plantations annually. In Canada, it is unknown which species are responsible for Phytophthora root rot (PRR) of cultivated Abies species. Between 2019 and 2021, soil and root samples were collected from 40 Christmas tree plantations in Québec province. We used soil baiting and direct isolation from unidentified root fragments to assess the diversity of culturable Phytophthora spp. The obtained isolates were identified using a multilocus sequencing and phylogenetic approach. A total of 44 isolates were identified, including eight P. chlamydospora, eight P. abietivora, seven P. gonapodyides, three P. gregata, six P. megasperma, and two P. kelmanii isolates, plus 10 isolates belonging to a previously unknown taxon that is phylogenetically close to P. chlamydospora and P. gonapodyides. Among the known species, P. abietivora was the most prevalent isolated species associated with trees showing aboveground PRR-like symptoms. Pathogenicity trials confirmed the pathogenicity potential of P. abietivora on both Fraser fir and balsam fir seedlings. Our study provides a first snapshot of the Phytophthora diversity in Québec's Christmas tree productions and describes multiple potential first associations between Phytophthora species and Abies balsamea and A. fraseri.[Formula: see text] Copyright © 2024 His Majesty the King in Right of Canada, as represented by the Minister of Natural Resources Canada. This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Worldwide forest surveys reveal forty-three new species in Phytophthora major Clade 2 with fundamental implications for the evolution and biogeography of the genus and global plant biosecurity

During 25 surveys of global Phytophthora diversity, conducted between 1998 and 2020, 43 new species were detected in natural ecosystems and, occasionally, in nurseries and outplantings in Europe, Southeast and East Asia and the Americas. Based on a multigene phylogeny of nine nuclear and four mitochondrial gene regions they were assigned to five of the six known subclades, 2a-c, e and f, of Phytophthora major Clade 2 and the new subclade 2g. The evolutionary history of the Clade appears to have involved the pre-Gondwanan divergence of three extant subclades, 2c, 2e and 2f, all having disjunct natural distributions on separate continents and comprising species with a soilborne and aquatic lifestyle and, in addition, a few partially aerial species in Clade 2c; and the post-Gondwanan evolution of subclades 2a and 2g in Southeast/East Asia and 2b in South America, respectively, from their common ancestor. Species in Clade 2g are soilborne whereas Clade 2b comprises both soil-inhabiting and aerial species. Clade 2a has evolved further towards an aerial lifestyle comprising only species which are predominantly or partially airborne. Based on high nuclear heterozygosity levels ca. 38 % of the taxa in Clades 2a and 2b could be some form of hybrid, and the hybridity may be favoured by an A1/A2 breeding system and an aerial life style. Circumstantial evidence suggests the now 93 described species and informally designated taxa in Clade 2 result from both allopatric non-adaptive and sympatric adaptive radiations. They represent most morphological and physiological characters, breeding systems, lifestyles and forms of host specialism found across the Phytophthora clades as a whole, demonstrating the strong biological cohesiveness of the genus. The finding of 43 previously unknown species from a single Phytophthora clade highlight a critical lack of information on the scale of the unknown pathogen threats to forests and natural ecosystems, underlining the risk of basing plant biosecurity protocols mainly on lists of named organisms. More surveys in natural ecosystems of yet unsurveyed regions in Africa, Asia, Central and South America are needed to unveil the full diversity of the clade and the factors driving diversity, speciation and adaptation in Phytophthora. Taxonomic novelties: New species: Phytophthora amamensis T. Jung, K. Kageyama, H. Masuya & S. Uematsu, Phytophthora angustata T. Jung, L. Garcia, B. Mendieta-Araica, & Y. Balci, Phytophthora balkanensis I. Milenković, Ž. Tomić, T. Jung & M. Horta Jung, Phytophthora borneensis T. Jung, A. Durán, M. Tarigan & M. Horta Jung, Phytophthora calidophila T. Jung, Y. Balci, L. Garcia & B. Mendieta-Araica, Phytophthora catenulata T. Jung, T.-T. Chang, N.M. Chi & M. Horta Jung, Phytophthora celeris T. Jung, L. Oliveira, M. Tarigan & I. Milenković, Phytophthora curvata T. Jung, A. Hieno, H. Masuya & M. Horta Jung, Phytophthora distorta T. Jung, A. Durán, E. Sanfuentes von Stowasser & M. Horta Jung, Phytophthora excentrica T. Jung, S. Uematsu, K. Kageyama & C.M. Brasier, Phytophthora falcata T. Jung, K. Kageyama, S. Uematsu & M. Horta Jung, Phytophthora fansipanensis T. Jung, N.M. Chi, T. Corcobado & C.M. Brasier, Phytophthora frigidophila T. Jung, Y. Balci, K. Broders & I. Milenković, Phytophthora furcata T. Jung, N.M. Chi, I. Milenković & M. Horta Jung, Phytophthora inclinata N.M. Chi, T. Jung, M. Horta Jung & I. Milenković, Phytophthora indonesiensis T. Jung, M. Tarigan, L. Oliveira & I. Milenković, Phytophthora japonensis T. Jung, A. Hieno, H. Masuya & J.F. Webber, Phytophthora limosa T. Corcobado, T. Majek, M. Ferreira & T. Jung, Phytophthora macroglobulosa H.-C. Zeng, H.-H. Ho, F.-C. Zheng & T. Jung, Phytophthora montana T. Jung, Y. Balci, K. Broders & M. Horta Jung, Phytophthora multipapillata T. Jung, M. Tarigan, I. Milenković & M. Horta Jung, Phytophthora multiplex T. Jung, Y. Balci, K. Broders & M. Horta Jung, Phytophthora nimia T. Jung, H. Masuya, A. Hieno & C.M. Brasier, Phytophthora oblonga T. Jung, S. Uematsu, K. Kageyama & C.M. Brasier, Phytophthora obovoidea T. Jung, Y. Balci, L. Garcia & B. Mendieta-Araica, Phytophthora obturata T. Jung, N.M. Chi, I. Milenković & M. Horta Jung, Phytophthora penetrans T. Jung, Y. Balci, K. Broders & I. Milenković, Phytophthora platani T. Jung, A. Pérez-Sierra, S.O. Cacciola & M. Horta Jung, Phytophthora proliferata T. Jung, N.M. Chi, I. Milenković & M. Horta Jung, Phytophthora pseudocapensis T. Jung, T.-T. Chang, I. Milenković & M. Horta Jung, Phytophthora pseudocitrophthora T. Jung, S.O. Cacciola, J. Bakonyi & M. Horta Jung, Phytophthora pseudofrigida T. Jung, A. Durán, M. Tarigan & M. Horta Jung, Phytophthora pseudoccultans T. Jung, T.-T. Chang, I. Milenković & M. Horta Jung, Phytophthora pyriformis T. Jung, Y. Balci, K.D. Boders & M. Horta Jung, Phytophthora sumatera T. Jung, M. Tarigan, M. Junaid & A. Durán, Phytophthora transposita T. Jung, K. Kageyama, C.M. Brasier & H. Masuya, Phytophthora vacuola T. Jung, H. Masuya, K. Kageyama & J.F. Webber, Phytophthora valdiviana T. Jung, E. Sanfuentes von Stowasser, A. Durán & M. Horta Jung, Phytophthora variepedicellata T. Jung, Y. Balci, K. Broders & I. Milenković, Phytophthora vietnamensis T. Jung, N.M. Chi, I. Milenković & M. Horta Jung, Phytophthora ×australasiatica T. Jung, N.M. Chi, M. Tarigan & M. Horta Jung, Phytophthora ×lusitanica T. Jung, M. Horta Jung, C. Maia & I. Milenković, Phytophthora ×taiwanensis T. Jung, T.-T. Chang, H.-S. Fu & M. Horta Jung. Citation: Jung T, Milenković I, Balci Y, Janoušek J, Kudláček T, Nagy ZÁ, Baharuddin B, Bakonyi J, Broders KD, Cacciola SO, Chang T-T, Chi NM, Corcobado T, Cravador A, Đorđević B, Durán A, Ferreira M, Fu C-H, Garcia L, Hieno A, Ho H-H, Hong C, Junaid M, Kageyama K, Kuswinanti T, Maia C, Májek T, Masuya H, Magnano di San Lio G, Mendieta-Araica B, Nasri N, Oliveira LSS, Pane A, Pérez-Sierra A, Rosmana A, Sanfuentes von Stowasser E, Scanu B, Singh R, Stanivuković Z, Tarigan M, Thu PQ, Tomić Z, Tomšovský M, Uematsu S, Webber JF, Zeng H-C, Zheng F-C, Brasier CM, Horta Jung M (2024). Worldwide forest surveys reveal forty-three new species in Phytophthora major Clade 2 with fundamental implications for the evolution and biogeography of the genus and global plant biosecurity. Studies in Mycology 107: 251-388. doi: 10.3114/sim.2024.107.04.