Abstract
In California, marguerite daisy (Argyranthemum frutescens [= Chyrsanthemum frutescens]) is an important, commercially grown, perennial flowering plant that is used as a potted plant, cutflower, and landscape plant. For two seasons (2003 and 2004), a downy mildew disease has been affecting marguerite daisy at wholesale container and field cutflower nurseries and retail nurseries in coastal California (Monterey, Santa Cruz, and San Mateo counties). The disease occurred early in the season (January) and continued to infect new foliage throughout the year whenever cool, foggy weather occurred. The disease primarily affected newly expanded young leaves on shoot tips. Such leaves were chlorotic, twisted and bent, and stunted. In some cases, leaflet tips turned black and necrotic. The abaxial sides of affected leaves were heavily colonized by the extensive purplish brown growth of downy mildew. Older, fully expanded foliage was unaffected. Flowers could be infected with the fungus growing on the undersides of petals and resulting in slightly twisted, bent shapes. Symptomatic plants and cutflower stems were unmarketable. Hyaline conidiophores emerged from stomata, branched dichotomously (rarely trichotomously), and had branches ending in slender, curved branchlets that did not have swollen tips. Conidia were slightly brown, ovoid, mostly nonpapillate, and measured 28.5 to 40.0 × 19.0 to 28.0 μm. Oospores were not observed in plant tissue. On the basis of symptoms and morphology of the organism, the pathogen was identified as Peronospora radii (1,2). To prove pathogenicity, plants were spray inoculated with conidial suspensions, incubated for 24 h in a dew chamber (18 to 20°C), and then maintained in a greenhouse (22 to 24°C).After 18 to 20 days, symptoms and signs of downy mildew developed only on the newest foliage of inoculated plants, and the pathogen morphology matched that of the originally observed pathogen. Untreated control plants did not develop downy mildew. To our knowledge, this is the first report of downy mildew caused by P. radii on marguerite daisy in California and the United States. The pathogen has not been reported on other hosts in California. P. radii is found on marguerite daisy in England, Germany, Israel, Mexico, and the former Yugoslavia (1,2). References: (1) I. S. Ben-Ze'ev et al. Phytoparasitica 15:51, 1987. (2) O. Constantinescu. Sydowia Ann. Mycol. 41:79, 1989.
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Claims 15
Claim · model-written summary
Downy mildew affected nursery marguerite daisies in coastal California in 2003 and 2004.
Verbatim
e0“For two seasons (2003 and 2004), a downy mildew disease has been affecting marguerite daisy at wholesale container and field cutflower nurseries and retail nurseries in coastal California”
Claim · model-written summary
Disease continued during cool foggy weather through the year.
Verbatim
e0“The disease occurred early in the season (January) and continued to infect new foliage throughout the year whenever cool, foggy weather occurred”
t0“Marguerite Daisy”
Claim · model-written summary
Young shoot-tip leaves were primarily affected.
Verbatim
e0“The disease primarily affected newly expanded young leaves on shoot tips”
t0“Marguerite Daisy”
Claim · model-written summary
Affected leaves were chlorotic, distorted, and stunted.
Verbatim
e0“Such leaves were chlorotic, twisted and bent, and stunted”
t0“Marguerite Daisy”
Claim · model-written summary
Some leaflet tips became black and necrotic.
Verbatim
e0“In some cases, leaflet tips turned black and necrotic”
t0“Marguerite Daisy”
Claim · model-written summary
Affected leaf undersides were heavily colonized by downy mildew.
- Taxon
- marguerite daisyt0
- Organ / stage
- affected leavese0
- Interactor
- downy mildewPeronosporaceaee0pathogen
- Outcome
- heavily colonizede0
Verbatim
e0“The abaxial sides of affected leaves were heavily colonized by the extensive purplish brown growth of downy mildew”
t0“Marguerite Daisy”
Claim · model-written summary
Older expanded foliage was unaffected.
Verbatim
e0“Older, fully expanded foliage was unaffected”
t0“Marguerite Daisy”
Claim · model-written summary
Flowers could be infected and deformed.
Verbatim
e0“Flowers could be infected with the fungus growing on the undersides of petals and resulting in slightly twisted, bent shapes”
t0“Marguerite Daisy”
Claim · model-written summary
Symptomatic plants and cut stems were unmarketable.
Verbatim
e0“Symptomatic plants and cutflower stems were unmarketable”
t0“Marguerite Daisy”
Claim · model-written summary
Conidia measured 28.5 to 40.0 × 19.0 to 28.0 μm.
Verbatim
e0“Conidia were slightly brown, ovoid, mostly nonpapillate, and measured 28.5 to 40.0 × 19.0 to 28.0 μm”
t0“Marguerite Daisy”
Claim · model-written summary
Oospores were not observed in plant tissue.
Verbatim
e0“Oospores were not observed in plant tissue”
t0“Marguerite Daisy”
Claim · model-written summary
The pathogen was identified as Peronospora radii.
- Taxon
- marguerite daisyt0
- Interactor
- Peronospora radii
Peronospora radiie0pathogen - Outcome
- identified as Peronospora radiie0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the pathogen was identified as Peronospora radii”
t0“Marguerite Daisy”
Claim · model-written summary
Inoculated plants developed downy mildew on newest foliage after 18 to 20 days.
- Taxon
- marguerite daisyt0
- Organ / stage
- newest foliagee0
- Treatment
- inoculated plantse0
- Interactor
- downy mildewPeronosporaceaee0pathogen
- Outcome
- symptoms and signs of downy mildewe0
- Value
- 18 to 20 dayse0
Not reportedComparatorDirection
Verbatim
e0“After 18 to 20 days, symptoms and signs of downy mildew developed only on the newest foliage of inoculated plants”
t0“Marguerite Daisy”
Claim · model-written summary
Untreated controls did not develop downy mildew.
- Taxon
- marguerite daisyt0
- Interactor
- downy mildewPeronosporaceaee0pathogen
- Outcome
- did not develop downy mildewe0
Verbatim
e0“Untreated control plants did not develop downy mildew”
t0“Marguerite Daisy”
Claim · model-written summary
This was the first California and US report of P. radii downy mildew on marguerite daisy.
- Taxon
- marguerite daisye0
- Interactor
- P. radiiPeronospora radiie0pathogen
- Outcome
- first report of downy mildewe0
- Setting
- California and the United Statese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“this is the first report of downy mildew caused by P. radii on marguerite daisy in California and the United States”