Chenopodium quinoa as a "universal" plant virus host
Summary
Chenopodium quinoa is a well known “universal” host. Virologists seem to prefer Nicotiana benthamiana since infections are usually systemic and leaves are reputedly “cleaner” for virus purification. C. quinoa in fact has many advantages; even local infections often give good virus yields. A brief test of four quinoa varieties shows similar susceptibility but slight differences in symptoms and time course of infection.
Prehistory of Chenopodium quinoa
Chenopodium quinoa, which resembles the common weed Chenopodium album, was cultivated by the Incas and is still cultivated in the altiplano of Bolivia and Peru. The plant is a pseudocereal; (protein rich) seeds are harvested.
Recent history of Chenopodium quinoa
Virologists “discovered” Chenopodium quinoa in the mid 50s (late in the host range age) coincident with the “famous” Hollings host range paper which described C. amaranticolor, not C. quinoa. Hollings recently notes that C. quinoa is not only a better virus host than C. amaranticolor, but that it contains fewer virus inhibitors. C. quinoa and N. benthamiana have not been systematically compared as hosts for a wide range of viruses.
Advantages and properties of Chenopodium quinoa
C. quinoa seeds are large enough to handle individually. Fresh seeds germinate uniformly. Seedlings (2 wk old seedlings) can be inoculated at 3 to 4 weeks. For many viruses symptoms appear quickly (as little as 2 or 3 days). C. quinoa grows best at warm temperatures, high light intensities and long days. Viruses are often symptomless on N. benthamiana; requiring additional assays to confirm infection . TMV contaminants systemically invade and kill N. benthamiana. TMV infects C. quinoa locally permitting separation of systemic viruses such as alfalfa mosaic and nepoviruses. Beware - Sowbane mosaic is an insidious contaminant. It’s natural host is sowbane (Chenopodium murale ). Aerial pollen containing SoMV contaminates inocula “converting” viruses to SoMV. Leaves of C. quinoa are covered with salt glands which are visible with a dissecting scope.
Purifying viruses from Chenopodium quinoa
“Minipurified” preps from C. quinoa compare in purity to those from other hosts. Preparations have more 25K to 27K proteins (phytoferritin?) than Nicotianas, but less than cowpea. Both virus and dsRNA can often be purified from locally infected leaves. Obviously C. quinoa is unsuitable for purifying a virus which gives only a few pinpoint lesions.
C. quinoa varieties
Four varieties were purchased - Dave (Four-0-Seven), Faro, Isluga and Temuco (Seeds of Change). Seedlings of these plus “greenhouse quinoa" were inoculated with brome mosaic, tobacco mosaic, beet soilborne mosaic and tobacco streak viruses. Symptoms on commercial varieties were substantially similar to those on “greenhouse quinoa”. Brome mosaic went systemic fastest on “greenhouse”; Dave (Four-0-Seven) survived TSV infection better than other varieties. An exception (Jan 2003). I recently isolated tobacco streak virus from a wild composite. It gives striking local lesions within three days and eventual systemic necrosis on greenhouse quinoa, but no lesions and mild systemic mottle on two other varieties. Plant genetic variation never ceases to surprise.
Detecting TMV in tobacco products
Pinto beans are recommended for detecting TMV. Though beans are convenient, TMV lesions are microscopic; the assay is insensitive. Inoculation of C. quinoa detected TMV in a Dominican cigar and roughly a third of cigarette butts, but not in any of ten locally purchased pipe tobaccos.
A recommended use for universal hosts
Old plants, deteriorating tissue and "unusual" hosts often have high ELISA and minipurification backgrounds. Inoculating a common host and testing young plants by ELISA or minipurification should improve reliability of detection.
Conclusions
C. quinoa is often a better diagnostic host than N. benthamiana. For viruses which do marginally well on “greenhouse quinoa", additional quinoa varieties are worth testing. Natural variation of C. quinoa as a virus host is worth further exploration.
Useful references
Hein, Alice (1957) Beitrage zur Kenntnis der Viruskrankheiten an Unkrautern. II. Das Luzernmosaik- und das Lamium-Gelbmosaikvirus. Phytopath Z 29, 79-116
Hollings, M. (1959) Host range studies with fifty two plant viruses. Ann Appl Biol 47, 98-108
National Research Council Staff (1980) “Lost Crops of the Incas” National Academy Press, Washington,DC
Uschdraweit, H.A. (1955) Das Grunscheckmosaik der Gurke. Chenopodium quinoa als Testpflanze fur das Gurkenmosaikvirus. NachrBl dtsch PflSchDienst (Braunschw) Stuttgart 7, 150-152
Web bibliography of C. quinoa
Whealy, Kent (1999) “
Garden Seed Inventory”. Seed Savers Exchange. Decorah, IA
Viruses which infect Chenopodium quinoa
Seeds available, E-mail: llane1@unl.edu