Plasmopara obducens

Plasmopara obducens is a species of oomycete that causes Impatiens downy mildew. It was first described on Impatiens noli-tangere in Germany in 1877. Plasmopara obducens is known from native species of Impatiens since the 1800s, but outbreaks on cultivated varieties of Impatiens walleriana started in 2003 in the United Kingdom and in 2004 in the United States. [1] The outbreak spread worldwide by 2016.[2]

Plasmopara obducens
Scientific classification
Clade: SAR
Phylum: Oomycota
Order: Peronosporales
Family: Peronosporaceae
Genus: Plasmopara
Species:
P. obducens
Binomial name
Plasmopara obducens
(J. Schröt.) J. Schröt., (1886)
Synonyms
  • Peronospora obducens J. Schröt., (1877)
  • Rhysotheca obducens (J. Schröt.) G.W. Wilson, (1907)
  • Peronospora impatientis Ellis & Everh., (1892)
  • Plasmopara impatientis (Ellis & Everh.) Berl., (1898)

Morphology

Sporangiophores are an average of 373 (260-484) micrometers with the first branch appearing at 197 (120-271) micrometers. Sporangia are 16 (13-18) micrometers by 13 (11-16) micrometers. [3] Resting spores are globose with a diameter of 28 micrometers [1]

Disease symptoms

Initially, leaves are stippled or yellowed. Infected leaves curl downward. A white down is often present on the underside of the leaves; buds and stems may also develop a down. Eventually, the leaves fall off the plant leaving just stems. [4] In about a week, the plants are dead.[2]

Taxonomy

J. Schröter originally placed the species in the genus Peronospora but later moved it to the genus Plasmopara. [5] Some authors believe the outbreaks on I. walleriana and I. balsamina are not caused by P. obducens but two new species P. destructor and P. velutina. [3]

References
  1. Shishkoff, Nina (2019). "The oospore state of Plasmopara obducens, impatiens downy mildew". Mycologia. 111 (4): 632–646. doi:10.1080/00275514.2019.1601986. PMID 31136264. S2CID 169033508.
  2. Derevnina, Lida; Petre, Benjamin; Kellner, Ronny; Dagdas, Yasin F.; Sarowar, Mohammad Nasif; Giannakopoulo, Artemis; De la Conception, Juan Carlos; Chaparro-Garcia, Angela; Pennington, Helen G.; van West, Pieter; Kamoun, Sophien (2016). "Emerging oomycete threats to plants and animals". Philosophical Transactions of the Royal Society B. 317.
  3. Görg, Marlena; Ploch, Sebastian; Kruse, Julia; Kummer, Volker; Runge, Fabian; Choi, Young-Joon; Thines, Marco (2017). "Revision of Plasmopara (Oomycota, Peronosporales) parasitic to Impatiens". Mycological Progress. 16 (8): 791–799. doi:10.1007/s11557-017-1316-y. S2CID 20243718.
  4. Rosetta, Robin (2014). "Downy mildew on impatiens". Retrieved July 4, 2019.
  5. "Kryotogamen-Flora von Schlesien". 3–1. 1886: 129–256. Cite journal requires |journal= (help)


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