Plasmopara echinaceae, a new species of downy mildew affecting cone flowers (Echinacea purpurea) in the United States.

Downy mildew is one of the most important diseases of commercial sunflower and other Asteraceae hosts, including ornamental Rudbeckia. Plasmopara halstedii has historically been identified as the causal agent of this disease, considered a complex of species affecting nearly 35 genera in various tribes. However, with the use of molecular DNA characters for phylogenetic studies, distinct lineages of P. halstedii in the Asteraceae have been identified, confirmed as distinct or segregated as new species. During August of 2022, a downy mildew was observed on potted Echinacea purpurea grown in a retail greenhouse in Jefferson County, Wisconsin, USA. Phylogenetic analyses of the cytochrome c oxidase subunit 2 (cox2) and nuclear large subunit ribosomal RNA (nc LSU rDNA) gene regions indicated these Plasmopara sp. isolates are not conspecific with P. halstedii. Based on phylogenetic evidence and new host association, the Plasmopara isolates from E. purpurea are here described as Plasmopara echinaceae. Diagnostic morphological characters for this new species were not observed when compared with other isolates of P. halstedii or other Plasmopara species found on Asteraceae hosts, and therefore a list of species-specific substitutions in the cox2 region are provided as diagnostic characters. As this study corresponds to the first observation of downy mildew in cone flowers, it is recommended to follow the required disease prevention guidelines to prevent outbreaks and the establishment of this plant pathogen in production sites. Citation: Salgado-Salazar C, Romberg MK, Hudelson B (2023). Plasmopara echinaceae, a new species of downy mildew affecting cone flowers (Echinacea purpurea) in the United States. Fungal Systematics and Evolution 12: 203-217. doi: 10.3114/fuse.2023.12.10.

Fungal Planet description sheets: 281-319.

Novel species of fungi described in the present study include the following from South Africa: Alanphillipsia aloeicola from Aloe sp., Arxiella dolichandrae from Dolichandra unguiscati, Ganoderma austroafricanum from Jacaranda mimosifolia, Phacidiella podocarpi and Phaeosphaeria podocarpi from Podocarpus latifolius, Phyllosticta mimusopisicola from Mimusops zeyheri and Sphaerulina pelargonii from Pelargonium sp. Furthermore, Barssia maroccana is described from Cedrus atlantica (Morocco), Codinaea pini from Pinus patula (Uganda), Crucellisporiopsis marquesiae from Marquesia acuminata (Zambia), Dinemasporium ipomoeae from Ipomoea pes-caprae (Vietnam), Diaporthe phragmitis from Phragmites australis (China), Marasmius vladimirii from leaf litter (India), Melanconium hedericola from Hedera helix (Spain), Pluteus albotomentosus and Pluteus extremiorientalis from a mixed forest (Russia), Rachicladosporium eucalypti from Eucalyptus globulus (Ethiopia), Sistotrema epiphyllum from dead leaves of Fagus sylvatica in a forest (The Netherlands), Stagonospora chrysopyla from Scirpus microcarpus (USA) and Trichomerium dioscoreae from Dioscorea sp. (Japan). Novel species from Australia include: Corynespora endiandrae from Endiandra introrsa, Gonatophragmium triuniae from Triunia youngiana, Penicillium coccotrypicola from Archontophoenix cunninghamiana and Phytophthora moyootj from soil. Novelties from Iran include Neocamarosporium chichastianum from soil and Seimatosporium pistaciae from Pistacia vera. Xenosonderhenia eucalypti and Zasmidium eucalyptigenum are newly described from Eucalyptus urophylla in Indonesia. Diaporthe acaciarum and Roussoella acacia are newly described from Acacia tortilis in Tanzania. New species from Italy include Comoclathris spartii from Spartium junceum and Phoma tamaricicola from Tamarix gallica. Novel genera include (Ascomycetes): Acremoniopsis from forest soil and Collarina from water sediments (Spain), Phellinocrescentia from a Phellinus sp. (French Guiana), Neobambusicola from Strelitzia nicolai (South Africa), Neocladophialophora from Quercus robur (Germany), Neophysalospora from Corymbia henryi (Mozambique) and Xenophaeosphaeria from Grewia sp. (Tanzania). Morphological and culture characteristics along with ITS DNA barcodes are provided for all taxa.

First Report of the Powdery Mildews Leveillula taurica and Podosphaera pannosa on Rose Periwinkle in the United States.

In April 2013, unthrifty rose periwinkle (Catharanthus roseus (L.) G. Don) from a residential garden in Mililani, HI, was sent to the Hawaii Department of Agriculture. Symptoms, present on all plants, included leaf chlorosis, defoliation, and premature flower drop with necrotic spots on the adaxial side of leaves corresponding to patches of grayish mildew-like growth on the abaxial side. Samples were collected and sent to USDA PPQ National Identification Services (NIS) for confirmation. At NIS, stereoscope examination of the plants revealed two distinct powdery mildews. One, on the stems and leaves, had dimorphic conidia, with lanceolate primary (54 to 72 × 14 to 22 µm) and cylindrical secondary conidia (49 to 75 × 11 to 21 µm) (n = 25 for each), both with a reticulate surface. This fungus was identified morphologically as Leveillula taurica (Lév.) G. Arnaud (1). The second powdery mildew appeared confined to the sepals and petals. The external hyphae of this fungus produced upright chains of cylindrical to ovoid conidia (up to eight per chain), which contained fibrosin bodies and measured 22 × 12 µm (n = 50) with straight foot cells averaging 43 µm long, placing this fungus in the genus Podosphaera Kunze (1). Plants containing both fungi were accessioned as BPI892677 in the US National Fungal Collection. For molecular characterization, genomic DNA of the Podosphaera was obtained by scraping conidia from a petal and extracting with Thermo Scientific's Lyse and Go PCR Reagent. DNA of the Leveillula was extracted from 5 mm2 of infected leaf using Qiagen's Plant mini kit. The ITS region of each fungus was amplified and sequenced directly with primers ITS1F and ITS4. Each consensus sequence was created from manually edited chromatograms, searched against NCBI's GenBank using MegaBLAST and phylogenetically analyzed in MEGA5.2 under maximum parsimony (MP) in context with most similar hits and representatives from phylogenetic studies (2,3). Sequences from types of these fungi are not available for comparison. The resulting Podosphaera phylogeny grouped the Podosphaera suspect (GenBank KF703448) within a clade of P. pannosa (e.g., AB525938; bootstrap = 90). The Leveillula phylogeny grouped the Leveillula suspect (KF703447) within a clade (bootstrap = 88) of L. taurica (e.g., AB044346), L. chrozophorae (AB044346), and L. elaeagni (AB048350). Although the ITS sequences of these taxa are phylogenetically indistinguishable, morphological characters differentiate each species and the suspect as L. taurica (1). L. taurica has been recorded on C. roseus in India and Korea (1). This is the first report of L. taurica on C. roseus in the United States. This is the first report of P. pannosa on C. roseus worldwide. P. pannosa is commonly known as a powdery mildew of Rosaceae hosts, and has also been reported on hosts in the Anacardaciae and Oleaceae (1). P. pannosa represents the second Podosphaera species reported on any member of the Apocynaceae, with P. sparsa reported on other Apocynaceae genera (1). The presence of two powdery mildew genera on different parts of the same plant could cause multiple forms of damage and impact the production of this popular landscape ornamental plant. References: (1) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No. 11. CBS, Utrecht, Netherlands, 2012. (2) S. A. Khodoparast et al. Mycol. Res. 105:909, 2001. (3) S. Takamatsu et al. Persoonia 24:38, 2010.

Phylogenetic relationships among global populations of Pseudomonas syringae pv. actinidiae.

ABSTRACT Pseudomonas syringae pv. actinidiae, the causal agent of canker in kiwifruit (Actinidia spp.) vines, was first detected in Japan in 1984, followed by detections in Korea and Italy in the early 1990s. Isolates causing more severe disease symptoms have recently been detected in several countries with a wide global distribution, including Italy, New Zealand, and China. In order to characterize P. syringae pv. actinidiae populations globally, a representative set of 40 isolates from New Zealand, Italy, Japan, South Korea, Australia, and Chile were selected for extensive genetic analysis. Multilocus sequence analysis (MLSA) of housekeeping, type III effector and phytotoxin genes was used to elucidate the phylogenetic relationships between P. syringae pv. actinidiae isolates worldwide. Four additional isolates, including one from China, for which shotgun sequence of the whole genome was available, were included in phylogenetic analyses. It is shown that at least four P. syringae pv. actinidiae MLSA groups are present globally, and that marker sets with differing evolutionary trajectories (conserved housekeeping and rapidly evolving effector genes) readily differentiate all four groups. The MLSA group designated here as Psa3 is the strain causing secondary symptoms such as formation of cankers, production of exudates, and cane and shoot dieback on some kiwifruit orchards in Italy and New Zealand. It is shown that isolates from Chile also belong to this MLSA group. MLSA group Psa4, detected in isolates collected in New Zealand and Australia, has not been previously described. P. syringae pv. actinidiae has an extensive global distribution yet the isolates causing widespread losses to the kiwifruit industry can all be traced to a single MLSA group, Psa3.

First Report of Leaf Spot of Dracaena reflexa Caused by Burkholderia gladioli Worldwide.

In December 2008 (austral summer), a new disease of Dracaena reflexa Lam. cv. Anita was observed in a postentry quarantine greenhouse near Auckland, New Zealand on plants imported from Costa Rica. Symptoms included rust-colored, water-soaked lesions with chlorotic margins approximately 5 by 10 mm. When the disease was first noticed, incidence approached 80%, but subsequent reduction in greenhouse temperature dramatically reduced symptom expression and lesions were only visible on some leaf tips. Bacteria consistently isolated from the lesions on King's medium B (KB) were cream-colored, shiny, and produced a yellow, diffusible, nonfluorescent pigment. All isolates were able to rot onion slices. On the basis of BIOLOG (Hayward, CA) carbon utilization profiles, isolates were initially identified as Burkholderia gladioli (Severini 1913) Yabuuchi et al. 1993 with a probability index of 100% and a similarity index of 0.85. For molecular identification, a near full-length sequence of the 16S rDNA gene was amplified from all isolates using primers fD2 and rP1 (1), obtaining a PCR product of approximately 1,500 bp. The nucleotide sequences were 100% identical to a number of B. gladioli GenBank entries, including Accession Nos. EF193645 and EF088209. To confirm pathogenicity, three isolates (two isolated prior to greenhouse temperature reduction and one after) were used. Three D. reflexa plants were inoculated per bacterial isolate by wounding three young fully expanded leaves on each plant (four wounds per leaf) and spraying the leaves with a bacterial suspension in sterile distilled water at 108 CFU/ml. At the same time, Gladiolus nanus plants were inoculated in a similar manner. Control plants (D. reflexa and G. nanus) were wounded and sprayed with sterile distilled water. All inoculated plants were covered with plastic bags to maintain humidity and placed in a growth chamber at 25°C. At 3 days, all inoculated plants began to show water soaking and reddish coloration around the inoculation sites, and by 7 days, the lesions had expanded to resemble natural infection. Bacteria isolated on KB from the leading edge of each lesion were morphologically identical to the initial isolates. No bacteria were recovered from the wound sites on the control plants. The 16S rDNA sequences of selected isolates from inoculated plants showed 100% identity to the sequences of the initial isolates, thereby fulfilling Koch's postulates. To our knowledge, this is the first report of B. gladioli causing leaf spot of D. reflexa in the world. Reference: (1) W. G. Weisburg et al. J. Bacteriol. 173:697, 1991.

Host Range and Phylogeny of Fusarium solani f. sp. eumartii from Potato and Tomato in California.

Fusarium solani f. sp. eumartii, historically considered solely a pathogen of potato (Solanum tuberosum), was associated with tomato plants (Lycopersicon esculentum) exhibiting foot rot symptoms in California. The pathogenicity of California isolates of F. solani f. sp. eumartii from potato plants with Eumartii wilt symptoms and tomato plants with foot rot symptoms was determined on potato, tomato, pepper (Capsicum anuum), and eggplant (S. melongena). Isolates from both potato and tomato caused dry rot symptoms on potato tubers and root or collar rot on all four host species in the greenhouse. In field trials, isolates from both tomato and potato were pathogenic on tomato, potato, and pepper, confirming that the host range of F. solani f. sp. eumartii is not limited to potato. The phylogeny of isolates from potato and tomato was determined based on sequences of two DNA fragments: rDNA internal transcribed spacer regions and partial sequences of elongation factor 1-α. All of the California isolates of F. solani f. sp eumartii from tomato and potato formed a single monophyletic clade distinct from other formae speciales and mating populations of F. solani. The results of this study demonstrate that Eumartii wilt and tomato foot rot in California both are caused by F. solani f. sp. eumartii.

Efficacy of Germination Stimulants of Sclerotia of Sclerotium cepivorum for Management of White Rot of Garlic.

The ability of soil-applied garlic powder and diallyl disulfide to stimulate germination of sclerotia of Sclerotium cepivorum, the cause of white rot of onion and garlic, was evaluated in four field trials. Because sclerotia germinate in response to exudation of specific volatile sulfides and thiols from allium roots, sulfides applied to the ground in the absence of an allium crop cause death of the sclerotia after they germinate and exhaust nutrient reserves. In this study, garlic powder and a synthetic garlic oil, diallyl disulfide, were incorporated into the soil in commercial fields naturally infested with S. cepivorum. Methyl bromide was included as a chemical control. Within 3 months after treatment, over 90% of the sclerotia died in the plots treated with the germinationstimulants, which was similar to the reduction of viable sclerotia achieved with an application of methyl bromide. The degree of sclerotial mortality in plots treated with garlic powder at 112 kg/ha or more was almost equal to that achieved by diallyl disulfide at 0.5 ml/m2 or methyl bromide at 448 kg/ha. Despite the efficacy of the stimulants and methyl bromide to reduce populations of sclerotia, the pathogen caused substantial root rot and yield losses in subsequent garlic crops planted about a year after soil treatment. However, germination stimulants have utility because the reduction of the vast majority of sclerotia in a field reduces the risk of spread of the pathogen to neighboring fields.

First Report of Powdery Mildew on Potato Caused by Golovinomyces cichoracearum in California.

In October 2003, potato plants in three fields (cv. Desiree, Satina, Midas, and Mondial) in Lancaster, California exhibited symptoms and signs of powdery mildew. Disease symptoms were most severe on cvs. Desiree and Santina. Disease expression was greater along sprinkler lines and in localized areas from which the disease spread to surrounding plants. Severely affected plants began collapsing just prior to water cutoff. Early symptoms comprise small dark areas on the adaxial surface of leaves, along the veins, and at the petioles. Dark lesions consisting of mycelia and conidiophores were also visible on the main stems of affected plants. As the disease progressed, leaves were covered by a gray powdery fungal mass, and older leaves became necrotic. Conidial chains arising from the hyaline, epiphytic mycelia consisted of two to eight conidia. The cylindric to doliform conidia measured 16.8 to 22.8 µm wide (mean = 19.2, standard error = 0.36, N = 30) × 28.8 to 45.6 µm long (mean = 32.4, standard error = 0.75, N = 30). No cleistothecia were observed. Identification of the causal agent as Golovinomyces cichoracearum (synonyms G. orontii and Erysiphe cichoracearum) based on morphology was confirmed by internal transcribed spacer (ITS)-polymerase chain reaction (PCR). Conidia were washed off the affected leaves, concentrated by filtration and centrifugation, and sonicated to release genomic DNA. PCR was performed on the sonicated conidia with primers ITS4 and ITS5 (2), and the resulting amplicon was purified and sequenced. BLAST analysis of the ITS sequence revealed a 99% homology to E. cichoracearum from an Ambrosia sp. (GenBank Accession No. AF011292). Pathogenicity was confirmed on potato seedlings cv. Red La Soda. Inoculations were performed twice on six plants (three pots) each time. A sterile brush was used to transfer conidia from the affected leaves to seedlings consisting of two to three fully expanded leaves. A plastic bag was placed around each pot containing two seedlings for 1 to 2 days and then removed. Noninoculated controls were stroked with a sterile brush, placed in a plastic bag for 1 to 2 days, and kept in the greenhouse on a separate bench. Two control plants were included for each inoculation. Plants were maintained in a greenhouse at approximately 25 to 28°C and 40 to 60% relative humidity. After 7 days, dark spots were visible on the leaves of all inoculated plants, and conidiophores with conidia identical to those of the isolate used as the inoculum source were apparent after 10 days. The controls showed no disease symptoms or signs. To our knowledge, this is the first report of powdery mildew caused by G. cichoracearum on potato in California. The first field report of the disease was from Washington in 1950 (1), with subsequent reports from Utah and Ohio. References: (1) J. D. Menzies. Plant Dis. Rep. 34:140, 1950. (2) T. J. White et al. PCR Protocols. Academic Press, New York, 1990.