Peronospora monardae, Hyaloperonospora daughtreyae and H. iberidis: new species associated with downy mildew diseases affecting ornamental plants in the United States

• Published in: European journal of plant pathology Vol. 157; no. 2; pp. 311 - 326
• Main Authors: Salgado-Salazar, Catalina, LeBlanc, Nicholas, Wallace, Emma C., Daughtrey, Margery L., Crouch, Jo Anne
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-06-2020; Springer Nature B.V
• Subjects: Agastache; Agriculture; Airborne microorganisms; Biomedical and Life Sciences; Cyclooxygenase-2; Downy mildew; Ecology; Genera; Haplotypes; Heterozygosity; Horticulture; Hyaloperonospora; Iberis; Life Sciences; Monarda didyma; New species; Ornamental plants; Pathogens; Peronospora; Phylogenetics; Phylogeny; Plant Pathology; Plant Sciences; Plants (botany); Oomycetes; Obligate parasites; Downy mildew
• ISSN: 0929-1873; 1573-8469
• DOI: 10.1007/s10658-020-01989-9

Species in the genera
Hyaloperonospora
and
Peronospora
(Oomycota, Peronosporaceae) are obligate biotrophic pathogens responsible for destructive downy mildew diseases of ornamental horticulture plants worldwide. Throughout the past decade, newly emergent downy mildew diseases have become increasingly prevalent, but often the identity of the pathogen is unknown or poorly defined. In this study we set out to identify the downy mildew pathogens infecting three widely grown ornamental plants:
Agastache
spp. (hyssops),
Tarenaya hassleriana
(syn. = 
Cleome hassleriana
; spider-flower) and
Monarda didyma
(bee balm or bergamot). Phylogenetic analysis of the internal transcribed spacer rDNA and
cox
2 revealed two new species, which are described here as
Peronospora monardae
infecting both
Monarda didyma
and
A. mexicana
, and
Hyaloperonospora daughtreyae
infecting
T. hassleriana.
One sample of
Peronospora
collected from
Agastache
sp. ‘Bolero’ did not cluster with
P. monardae
, but its relationship to other species in the clade was not sufficiently resolved for taxonomic determination. Phylogenetic analysis also supported the combination of
Peronospora iberidis
, a pathogen of
Iberis
spp. (candytuft), into
Hyaloperonospora
. To assess intrasample ITS sequence variation from
P. monardae
, data were generated using high-throughput amplicon sequencing (HTAS). Multiple haplotypes were identified from the
P. monardae
samples, with less than 1% intrasample variation observed. From a core set of haplotypes shared across the HTAS the variant frequencies could not be completely explained by heterozygosity alone.