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Peronospora farinosa
Pseudoperonospora effusa onSpinacia oleracea 'Breedblad scherpzaad'
Scientific classification
Domain:	Eukaryota
Clade:	Diaphoretickes
Clade:	SAR
Clade:	Stramenopiles
Phylum:	Oomycota
Order:	Peronosporales
Family:	Peronosporaceae
Genus:	Peronospora
Species:	P. effusa
Binomial name
Peronospora effusa (Grev.) Rabenh. (1854)
Synonyms
Botrytis effusa Grev. (1824)

Peronospora farinosa is a species name that has been widely applied to downy mildew on leaves of wild and cultivated Amaranthaceae: Amaranthus, Atriplex, Bassia, Beta, Chenopodium, Halimione, Salsola, Spinacia, etc. However, the species name has been taxonomically rejected (see report 20 from the Nomenclature Committee for fungi) as the original description contained reference to multiple species and could not unequivocally be attributed to a species of Peronospora. In the past, some of the species on important crop plants have been given names as formae speciales, notably f.sp. betae on sugar beet (= P. schachtii) and f.sp. spinaciae on spinach (= P. effusa). However, phylogentic reconstructions have revealed that these "forms" of Peronospora on different genera and their subdivisions, are distinct species, most of which already have previously published scientific names (see Index Fungorum). Such host specialization possibly also exists with respect to the various wild amaranthaceous species given as hosts of P. farinosa.

Downy mildew is a moderately important disease of sugar beet (Beta vulgaris). The pathogen persists as oospores in the soil, or on beet seed crops, or on overwintered volunteer beet plants. Attacks are most important at the seedling stage. The cotyledons are systemically infected, becoming discoloured and distorted. Loss of seedlings causes uneven crop development. Beet leaves are less affected, so a crop can to a substantial effect recover from an attack on seedlings. Control relies on adequate crop rotation and avoidance of sources of infection (e.g. adequate control of the disease on beet seed crops), as oospores survive only 2–3 years in the soil. Individual infected plants may also be removed. It is not generally necessary to apply fungicides.

Downy mildew has more direct importance on spinach (Spinacia oleracea), since it affects the harvested part (leaves). Yellow lesions appear on the older leaves. If rotating crops and removing individual infected plants fails, fungicide treatments are effective, and resistant cultivars are available.

References

1. Holliday P (2001). A Dictionary of Plant Pathology (2nd ed.). Cambridge University Press. ISBN 978-0-521-59458-5.
2. Choi, Young-Joon; Klosterman, Steven J.; Kummer, Volker; Voglmayr, Hermann; Shin, Hyeon-Dong; Thines, Marco (May 2015). "Multi-locus tree and species tree approaches toward resolving a complex clade of downy mildews (Straminipila, Oomycota), including pathogens of beet and spinach". Molecular Phylogenetics and Evolution. 86: 24–34. doi:10.1016/j.ympev.2015.03.003. PMC 5736102. PMID 25772799.
3. Brandenburger W (1985). Parasitische Pilze an Gefässpflanzen in Europa. Gustav Fischer Verlag. ISBN 978-3-437-30433-0.
4. ^ Smith IM, Dunez J, Lelliott RA, Phillips DH, Archer SA, eds. (1988). European Handbook of Plant Diseases. Blackwell Scientific Publications. ISBN 978-0-632-01222-0.
5. OEPP; EPPO (1997). Beet. EPPO Standards PP2 Good Plant Protection Practice, no. 12. European and Mediterranean Plant Protection Organization.

Further reading

• Yamauchi, Norihito; Horinouchi, Hayato; Sakai, Kazuhiko (July 2011). "First report of spinach downy mildew caused by race Pfs:8 of Peronospora farinosa f. sp. spinaciae in Japan". Journal of General Plant Pathology. 77 (4): 260–262. doi:10.1007/s10327-011-0313-2. S2CID 22237073.

• Water mould plant pathogens and diseases
• Vegetable diseases
• Peronosporales
• Protists described in 1824
• Oomycete species