Sweetpotato feathery mottle virus

Taxonomy

Although rarely recognised, SPFMV is responsible for considerable yield reduction in sweetpotato crops worldwide.  In the field, virus-free sweetpotato plants yield from 20% to over 100% more than infected plants.  Sensitive cultivars may suffer significant yield losses in comparison with tolerant ones.

Some isolates of SPFMV cause economic losses by their effect on storage root quality (internal cork and russet crack).

Geographical distribution

Worldwide. SPFMV is found wherever sweetpotato is grown.

Symptoms

Symptoms of SPFMV on the foliage are generally slight or absent. The classic irregular chlorotic patterns (feathering) along leaf veins and faint-to-distinct chlorotic spots with or without purple margins occur in some cultivars. Symptom visibility on foliage is influenced by cultivar susceptibility, degree of stress, growth stage, and strain virulence. Increased stress can lead to symptom expression, whereas rapid growth may result in symptom remission. Symptoms on storage roots depend on the strain of SPFMV and the sweetpotato variety. The common strain causes no symptom on storage roots of any variety, but the “russet crack” and “internal cork” strains cause external and internal dark necrotic lesions on certain varieties, respectively.

The virion, ranging from 810 to 865 nm long, contains a single, positive-sense strand of RNA with a Mr of approximately 3.7 x 10⁶ D and a polypeptide with a of 36 to38 KD. It has shown a serological relationship to some other potyviruses.

SPFMV is the most thoroughly characterized sweetpotato virus. SPFMV has many of the biological and biochemical properties, and cytopathic characteristics of potyviruses, including aphid transmissibility, occurrence of pinwheel inclusions, and a relatively narrow host range. SPFMV is sap-transmissible, and transmitted by a large number of aphid species such as Aphis gossypii, A. craccivora, Myzus persicae, in a nonpersistent manner. Vegetative propagation perpetuates the virus.

Several isolates and strains of SPFMV have been characterized in different parts of the world; perhaps the most important ones being the ordinary (O), russet crack (RC) and severe (S) strains because they directly affect storage root quality.

SPFMV is found with SPCSV in several countries; the combination usually results in a severe disease known as sweetpotato virus disease (SPVD).

Host range

Sweetpotato (Ipomoea batatas) is the main natural host of SPFMV, although the virus occurs in wild Ipomoea species. The experimental host range of the virus is mainly restricted to the Convolvulaceae and Chenopodiaceae, but a few strains also infect species of the Solanaceae of which Nicotiana benthamiana is a good propagation host for purification of the virus. Several strains cause local lesions on Chenopodium amaranticolor and C. quinoa.

Chenopodiaceae: Chenopodium murale, C. amaranticolor, C. quinoa, and Spinacia oleracea (several strains).

Convolvulaceae: Calonyction aculeatun, Ipomoea hederaceae, I. incarnata, I. lacunosa, I. purpurea, I. trichocarpa, I. tricolor, I. wrightii, Merremia sibirica, and Quamoclit lobata.

Solanaceae: Datura metel, Nicotiana benthamiana, N. clevelandii, N. occidentalis, and N. tabacum (some strains).

Aphid control is not economically feasible. The main control measures are avoidance of diseased plants as planting material, sanitation, and the use of resistant varieties. As SPFMV is perpetuated between cropping cycles in infected cuttings, the lack of symptoms in the foliage makes it difficult for farmers to select SPFMV-free cuttings.

Ames, T., Smit, N.E.J.M., Braun, A.R., O’Sullivan, J.N., and Skoglund, L.G. 1996. Sweetpotato: Major pests diseases, and nutritional disorders. International Potato Center (CIP). Lima, Perú. 152 p.

Brunt, A.,Crabtree, K., and Gibbs, A. (eds.). 1990. Viruses of tropical plants: Descriptions and lists from the VIDE database. CAB International, Wallingford, UK.

Brunt, A.A., Crabtree, K., Dallwitz, M.J., Gibbs, A.J., Watson, L. and Zurcher, E.J. (eds.) (1996 onwards). `Plant Viruses Online: Descriptions and Lists from the VIDE Database. Version: 20^th August 1996.' URL http://biology.anu.edu.au/Groups/MES/vide/

Campbel, R.N. Hall, D.H., and Mielines, N.M. 1974. Etiology of sweetpotato russet crack disease, Phytopathology, 64:210-218.

Clark, C.A., Derrick, K.S., Pace, C.S., and Watson, B. 1986. Survey of wild Ipomoea spp. as potential reservoirs of sweetpotato feathery mottle virus in Louisiana. Plant Disease, 70: 931-932.

Clark, C.A., and Moyer, J.M. 1988. Compendium of sweetpotato diseases. The American Phytopahological Society. APS Press, Minnesota, USA. 74 p.

Moyer, J.W., and Cali, B.B. 1985. Properties of sweetpotato feathery mottle virus RNA and capsid protein. Journal of General Virology, 66: 1185-1189.

Moyer, J.W., Cali, B.B., Kennedy, G.G., and Abou-Ghadir, F. 1980. Identification of two sweetpotato feathery mottle virus strains in North Carolina. Plant Disease, 64: 762-764.

Palomar, M.K., Barsalote, E.A. and Colis, H.S.V. 2000.  Distribution, transmission and diseases of sweetpotato feathery mottle virus. Ann. Trop. Res. 22 (1&2):16-30.

Contributed by:  Segundo Fuentes and Luis Salazar

Taxonomy

Economic importance

Geographical distribution

Symptoms

Morphology

Ecology

Host range

Management

References

Plant  with SPFMV showing yellowing of leaf veins ("vein clearing") (S. Fuentes & L. Salazar).

Chlorotic spots on leaves with and without purple rings (S. Fuentes & L. Salazar).

Leaf vein feathering without pigmentation (Left - C. Clark) and bordered with purple antocyanin pigment (Right - S. Fuentes & L. Salazar).

Purpling around chlorotic spots may be separated ring-spots (Left - E. van de Fliert) or fill the area between spots (Right - R. Thijssen).

External root lesions induced by the russet crack strain of SPFMV in storage roots (S. Fuentes & L. Salazar; C. Clark).

Detail of russet crack lesions (E. Coleman)

Internal root necrosis ("Internal Cork") attributed to SPFMV (J. Moyer, APS).