Albugo occidentalis (white rust of spinach)

Taxonomy

Domain	Eukarya
Kingdom	Chromista
Phylum	Oomycota
Class	Oomycetes
Subclass	Albuginomycetidae
Order	Albuginales
Family	Albuginaceae
Genus	Albugo

Scientific Name

Albugo occidentalis

Common Name

white rust

Author:Tom Creswell, Purdue University

Reviewed by: Dan Egel, Purdue University

Pathogen

Albugo occidentalis is an Oomycete, first described by G.W. Wilson in the Bulletin of the Torrey Botanical Club from New York state in 1907. Vakalounakis reports the pustules on spinach as ranging from 0.5 to 2.0 mm diameter and up to 3 mm in lenght. Sporangia developed in chains and when moist were 19.1 (14.1 to 23.5) um X 15.3 (12.9 to 20.0).

Symptoms and Signs

Raised white pustules form on the undersides of infected leaves and often coalesce. The appearance of the upper leaf surface is typically light yellow. The disease drastically reduces quality and marketability of the leaves.

Ecology and Spread

Albugo spp. are favored by cool moist weather and prolonged fog or dew. Sporangia may be distributed by wind, wind-blown rain, insects or movement of infected plant material during cultivation. The pathogen may overwinter in infected crop debris and infected weeds (Chenopodium spp. in the case of Albugo occidentalis). The white rust pathogen on crucifers is reported to only infect that group of plants.

Geographic Distribution

This fungus-like organism is widely reported on spinach in the US, and in Canada, China, Greece and Iran. It is also reported to infect several Chenopodium spp. and Monolepis nuttalliana.

Management

Crop rotation can help reduce disease incidence. Spinach lacks a single dominant gene for resistance and completely resistant cultivars have not been developed, however there are several cultivars with partial resistance; including Green Valley II, Ozarka II, Coho and Fall Green. Consult your local extension specialist or agent for variety and fungicide recommendations relevant to your particular state. Remember: the label is the law.

Diagnostic procedures

Visual and microscopic identification of the distinctive white, raised pustules on the lower leaf surface and sporangia of correct size is sufficient for morphological confirmation on spinach and other known hosts. For suspected cases on new hosts genomic DNA should be extracted from the ITS region of rDNA, ITS 1-5, 8S-ITS2 and COX2 mitochondria gene for amplification and sequence followed by Koch's postulates.

Resources and References

• D.J. Vakalounakis, A.G. Doulis, First Record of White Rust, Caused by Albugo occidentalis, on Spinach in Greece. Plant Disease 97:1253 http://dx.doi.org/10.1094/PDIS-02-13-0198-PDN
• G.W. Wilson, Bull. Torrey Bot. Club 34:61, 1907.

Acknowledgments

• National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30818 as part of "Diagnostic Image Series Development for Supporting IPM in the North Central Region" (USDA-NIFA-RIPM-003349)