Peronospora farinosa

Peronospora farinosa is a plant pathogen. It causes downy mildew on leaves of wild and cultivated Amaranthaceae: Amaranthus, Atriplex, Bassia, Beta, Chenopodium, Halimione, Salsola, Spinacia, etc. In the past, the forms of Peronospora on these different genera, and their species, were given different species names,[1] but these downy mildews are now generally considered to be forms of one species, P. farinosa (see Index Fungorum). Some of the forms on important crop plants have been given names as formae speciales,[2] notably f.sp. betae on sugar beet (= P. schachtii) and f.sp. spinaciae on spinach. Such host specialization possibly also exists with respect to the various wild amaranthaceous hosts of P. farinosa.

Peronospora farinosa
Pseudoperonospora farinosa f.sp. spinaciae at Spinacia oleracea 'Breedblad scherpzaad'
Scientific classification
Kingdom:	Chromista
Phylum:	Oomycota
Order:	Peronosporales
Family:	Peronosporaceae
Genus:	Peronospora
Species:	P. farinosa
Binomial name
Peronospora farinosa (Fr.) Fr. (1849)
Forma specialis
Peronospora farinosa f.sp. betae
Synonyms
Botrytis effusa Grev. (1824) Botrytis farinosa Fr. (1832) Peronospora chenopodii Schltdl. (1852) Peronospora effusa (Grev.) Rabenh. (1854) Peronospora variabilis Gäum.

Downy mildew is a moderately important disease of sugar beet (Beta vulgaris).[3] 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.[4]

Downy mildew has more direct importance on spinach (Spinacia oleracea),[3] 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. Brandenburger W (1985). Parasitische Pilze an Gefässpflanzen in Europa. Gustav Fischer Verlag. ISBN 978-3-437-30433-0.
2. Holliday P (2001). A Dictionary of Plant Pathology (2nd ed.). Cambridge University Press. ISBN 978-0-521-59458-5.
3. 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.
4. 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.