Phylogeographic and Phylogenomic Structure of the Quarantine Plant Pathogen Colletotrichum liriopes, Including New Reports in the United States.

Global agricultural trade has accelerated the emergence and re-emergence of new plant pathogens. In the United States, the fungal pathogen Colletotrichum liriopes is still considered a foreign quarantine pathogen that affects ornamental plants (i.e., Liriope spp.). Even though this species has been reported in East Asia on various asparagaceous hosts, its first and only report in the United States was in 2018. However, that study used only ITS nrDNA for identification, and no available culture or voucher specimen was maintained. The main objective of the present study was to determine the geographic and host distribution of specimens identified as C. liriopes. To accomplish this, new and existing isolates, sequences, and genomes obtained from various hosts and geographic locations (i.e., China, Colombia, Mexico, and the United States) were compared with the ex-type of C. liriopes. Multilocus phylogenetic (ITS, Tub2, GAPDH, CHS-1, and HIS3), phylogenomic, and splits tree analyses revealed that all the studied isolates/sequences form a well-supported clade with little intraspecific variation. Morphological characterizations support these findings. The minimum spanning network, low nucleotide diversity, and negative Tajima's D from both multilocus and genomic data suggest that there was a recent movement/invasion of a few East Asian genotypes to other countries where the ornamental plants are produced (e.g., South America) and subsequently to the importing countries, such as the United States. The study reveals that the geographic and host distribution of C. liriopes sensu stricto is expanded to the United States (i.e., at least Maryland, Mississippi, and Tennessee) and on various hosts in addition to Asparagaceae and Orchidaceae. The present study produces fundamental knowledge that can be used in efforts to reduce costs or losses from agricultural trade and to expand our understanding of pathogen movement.

Peronospora kuewa, sp. nov., a new downy mildew species infecting the endangered Hawaiian plant Plantago princeps var. princeps.

Plantago princeps var. princeps is an endangered native Hawaiian plant, and part of the recovery plan includes repopulation using plants grown in a nursery. However, disease pressure from downy mildew is hindering repopulation efforts. The organism associated with the downy mildew was determined to be a Peronospora species with brown, ellipsoid conidia measuring 21 by 16 µm on average, which was morphologically different from validly described species of Peronospora that infect Plantago species, but it was morphologically similar to the invalidly published species Peronospora lanceolatae (Art. 40.1). Comparison of mitochondrial cytochrome oxidase subunit I (cox1), mitochondrial cytochrome oxidase subunit II (cox2), nuclear internal transcribed spacer (ITS), and nuclear 28S rRNA D1-D2 (28S) loci revealed the unknown Peronospora to be molecularly divergent from Peronospora alta and Peronsopora plantaginis, but very similar to Peronospora from Plantago lanceolata, the type host of P. lanceolatae. Phylogenetic trees inferred with maximum likelihood and Bayesian inference from a concatenated alignmaent and individual gene trees confirmed the divergence of the unknown Peronospora from P. alta and P. plantaginis and its similarity to P. lanceolatae. However, attempts to inoculate Plantago lanceolata with the strain from Plantago princeps var. princeps were unsuccessful, which, in conjunction with divergence in ITS, suggests that the unknown Peronospora is specific to Plantago princeps var. princeps. Herein, the Peronospora strain on Plantago princeps var. princeps is described as the new species Peronospora kuewa based on morphology, molecular phylogenetics, and host specificity. In addition, Peronospora gaponenkoae is described here to honor Nina Ivanova Gaponenko on the basis of her description of P. lanceolatae.

Entyloma helianthi: identification and characterization of the causal agent of sunflower white leaf smut.

White leaf smut is a minor foliar disease of sunflower (Helianthus annuus) in the United States. The disease occurs primarily in greenhouse-grown sunflowers in California and causes leaf spot, defoliation, and a reduction in yield and crop value. Historically, many Entyloma specimens with similar morphological characters, but infecting diverse plant genera including Helianthus, were called Entyloma polysporum. Recent comparative morphological and molecular work has shown that Entyloma species infect hosts within a single genus or species, suggesting that the sunflower Entyloma species may not be E. polysporum. In 2015, sunflower leaf smut material was collected from ornamental sunflowers in a greenhouse in Santa Barbara County, California. Morphologically, this species differed from E. polysporum in having smaller, more regular-shaped teliospores and prominently developed conidiophores with cylindrical conidia. The rDNA ITS1-5.8S-ITS2 (internal transcribed spacer [ITS]) region of the sunflower leaf smut was phylogenetically distinct from all previously sequenced Entyloma species and found only on H. annuus. This study confirms that the sunflower leaf smut pathogen represents a novel species, Entyloma helianthi. Possible misidentification of the anamorphic stage of Entyloma helianthi as another leaf spot pathogen, Ramularia helianthi, is also discussed.

Microcyclic rusts of hollyhock ( Alcea rosea ).

Rust fungi infecting hollyhock and other plants in Malveae are frequently intercepted at ports of entry to the USA, particularly Puccinia malvacearum and P. heterogenea. These two species can be difficult to distinguish and can be further confused with other, less common species of microcyclic rust fungi infecting hollyhock: P. heterospora, P. lobata, P. platyspora, and P. sherardiana. Molecular phylogenetic analysis revealed that P. malvacearum and P. heterogenea are closely related, along with P. sherardiana and P. platyspora. A key to the six microcyclic Puccinia species infecting hollyhock is presented.