Abstract
In May 1999, marshelder (Iva xanthifolia Nutt.) plants with chlorotic upper leaves and abundant white sporulation on abaxial surfaces were observed in roadside ditches near Fargo, ND. Ovoid to elliptical zoosporangia (20 to 30 μm × 15 to 20 μm) that were borne on sporangiophores 400 to 500 μm long and branched monopodially at right angles were recovered from infected marshelder leaves. Dimensions of the zoosporangia and sporangiophores fall within those reported for Plasmopara halstedii (Farl.) Berl. & de Toni (1). Zoosporangia rinsed from marshelder plants were used to inoculate 3-day-old sunflower seedlings. The seedlings were immersed in a suspension of 2 × 10 4 zoosporangia per ml for 3 h, and planted in a greenhouse maintained at 18 to 24°C with a 16-h photoperiod. Systemic chlorosis, stunting, and sporulation were observed on sunflower plants 12 days after inoculation. Isolates from two individual marshelder plants were inoculated on a standard set of nine sunflower downy mildew differential lines, and were identified as race 3 (virulence pattern 700) and race 4 (virulence pattern 730). The marshelder isolates were evaluated for metalaxyl sensitivity by a soil drench inoculation method. Seed of an oilseed sunflower hybrid commercially treated with metalaxyl (138 g a.i./100 kg of seed) were planted in flats filled with sand and perlite (1:1, vol/vol). Three days after planting, the flats were drenched with a zoosporangial suspension (2 × 10 4 zoosporangia per ml) for four consecutive days. Both isolates produced 100% infection on plants grown from metalaxyl-treated seed, indicating the isolates were metalaxyl-insensitive. While over 80 species within 35 Compositae genera are reported to be hosts for P. halstedii, this is the fourth report of pathogenicity on sunflower by zoospores originating from other genera, the other three being Ambrosia (ragweed) (4), Dimorphotheca (cape marigold) (2) and Xanthium (cocklebur) (3). The cross-infectivity of the P. halstedii from Ambrosia, Iva, and Xanthium indicates that Compositae weeds may serve as a reservoir of P. halstedii to infect cultivated sunflower, and these weeds may help to perpetuate the metalaxyl-insensitive strain of P. halstedii. References: (1) G. Hall, Mycopathologia 106:205, 1989. (2) E. E. Leppik, Plant Dis. Rep. 49:940, 1965. (3) F. Viranyi, Helia 7:35, 1985. (4) I. Walcz et al. Helia 33:19, 2000.
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Claims 5
Claim · model-written summary
Marshelder showed chlorosis and white sporulation near Fargo.
.jpg?width=60){kind=small}
IvaOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
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Verbatim
e0“marshelder (Iva xanthifolia Nutt.) plants with chlorotic upper leaves and abundant white sporulation on abaxial surfaces were observed in roadside ditches near Fargo, ND.”
Claim · model-written summary
Inoculated sunflower developed systemic chlorosis, stunting and sporulation after 12 days.
- Taxon
- sunflower
Helianthus annuuse0 - Treatment
- inoculatione0
- Outcome
- Systemic chlorosis, stunting, and sporulatione0
- Qualifier
- 12 days after inoculatione0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Systemic chlorosis, stunting, and sporulation were observed on sunflower plants 12 days after inoculation.”
Claim · model-written summary
Marshelder isolates were identified as sunflower downy mildew races 3 and 4.
- Taxon
- sunflowerHelianthus annuuse0
- Outcome
- race 3 (virulence pattern 700) and race 4 (virulence pattern 730)e0
Not reportedInteractor
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Isolates from two individual marshelder plants were inoculated on a standard set of nine sunflower downy mildew differential lines, and were identified as race 3 (virulence pattern 700) and race 4 (virulence pattern 730).”
Claim · model-written summary
Both isolates caused complete infection of metalaxyl treated sunflower, implying insensitivity.
Not reportedTaxonComparatorDirection
Verbatim
e0“Both isolates produced 100% infection on plants grown from metalaxyl-treated seed, indicating the isolates were metalaxyl-insensitive.”
Claim · model-written summary
The authors infer Compositae weeds may reservoir pathogen infection for cultivated sunflower.
- Taxon
- sunflowerHelianthus annuuse0
- Interactor
- P. halstedii
Plasmopara halstediie0pathogen - Outcome
- infect cultivated sunflowere0
- Qualifier
- Compositae weeds may serve as a reservoire0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Compositae weeds may serve as a reservoir of P. halstedii to infect cultivated sunflower”
The same questions in other papers
inoculation · physiology: pigments · Helianthus annuus (common sunflower)Positive and negative results
2 papers in the same direction as this paper · 11 in the opposite direction
- positive
- positive
- positive
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See all 14 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.