Phytoplasma - sweetpotato
Contributors to this section: CIP, Lima, Peru (Carols Chuquillanqui, Segundo Fuentes, Ivan Manrique, Giovanna Muller, Willmer Pérez, Reinhard Simon, David Tay, Liliam Gutarra); CIP, Nairobi, Kenya (Ian Barker); FERA, UK (Derek Tomlinson, Julian Smith, David Galsworthy, James Woodhall).
Sweetpotato witches' broom
Sweetpotato little leaf
The disease primarily effects yield by reducing the number of roots. Yield reductions of more than 50 % have been recorded (Pearson et al.,1984).
Symptoms of vein clearing, small leaves (“little leaf”) frequently chlorotic with a more rounded shape, often curling at the leaf margins, stunting of plants, growth habit tends to be more erect than in healthy plants, proliferation of axillary shoots, together with a greatly reduced root system, result in weak plants with a compressed or bushy appearance. The number and quality of tubers are diminished and production of latex in vines and roots is also reduced (Gibb et al., 1995; Pearson et al., 1984; Clark and Moyer,1988 ; CABI, 2007; Mogen et al., 2008).
Sweetpotato little leaf has been reported in sweetpotato, Ipomoea pes-caprae (beach morning glory), Pharbitis nil (Japanese morning glory) and Pharbitis purpurea (Tall morning glory), Vigna unguiculata var. sesquipedalis and Lycopersicon esculentum (Saqib et al., 2006).
Asia, Africa, Oceania.
Biology and transmission
Sweetpotato little leaf can be transmitted by Orosius lotophagorum ryukyuensis. This leafhopper vector can transmit this phytoplasm between infected and healthy plants of Ipomoea spp. As the pathogen has a very long latent period, up to 283 days by graft transmission, infected planting material can appear healthy (Jackson and Zettler, 1983, CABI, 2007).
Detection/indexing method in place at the CGIAR Center
- At CIP, the phytoplasma is detected by grafting on the indicator plant I. setosa and by PCR.
- In seed certification schemes, no phytoplasm infections must be tolerated during the growing season. Stocks of in vitro cultures used for propagation should be from pathogen-free plants and maintained under conditions designed to prevent infection and contamination.
Procedure followed at CIP in case of a positive test
- At CIP if the pathogen is detected the imported germplasm must be cleaned by thermotherapy.
References and further reading
Ames T, Smit NEJM, Braun AR, O'Sullivan JN, Skoglund LG. 1997. Sweetpotato: Major pests, diseases, and nutritional disorders. International Potato Center.Lima, Peru. 1997. 153 p.
CABI 2007. Crop Protection Compendium. [online] Available from URL: www.cabi.org/compendia/cpc/. Commonwealth Agricultural Bureau International (CABI), Wallingford, UK. Date accessed 10 May 2010
Clark CA, Moyer JW. 1991. Compendium of Sweet Potato Diseases. Centro Internacional de la Papa (CIP). Lima, Peru. 97 p.
Gibb KS, Padovan AC, Mogen BD. 1995. Studies on sweat potato little-leaf Phytoplasma detected in sweet potato and other plant species growing in northern Australia. Phytopathology 85 (2):169–174
Jackson GVH, Zettler FW. 1983. Sweet potato witches' broom and legume little-leaf diseases in the Solomon Islands. Plant Disease, 67(9):1141–1144
Mogen BD, Pearson MN, Keane PJ, Thiagalingham K. 2008. Little Leaf: A Disease of Sweet Potato in Papua New Guinea Probably Caused by Mycoplasma-Like Organisms. Journal of Phytopathology 109(3):269 –276
Pearson MN, Keane PJ, Thiagalingham K. 1984. Little leaf: a disease of sweet potato in Papua New Guinea probably caused by mycoplasma-like organisms. Phytopathologische Zeitschrift, 109(3):269–276
Pearson MN, Keane PJ, Thiagalingham K. 2008. Little Leaf: A Disease of Sweet Potato in Papua New Guinea Probably Caused by Mycoplasma-like Organisms. Journal of Phytopathology 109 (3):269–276
Saqib M, Bayliss KL, Jones MGK. 2006. Identification of sweet potato little leaf phytoplasma associated with Vigna unguiculata var. sesquipedalis and Lycopersicon esculentum. Australasian Plant Pathology 35(3) 293–296
Seed Health General Publication Published by the Center or CGIAR
Moyer JW, Jackson GVH, Frison EA. (eds.). 1989. FAO/IBPGR Technical Guidelines for the Safe Movement of Sweet Potato Germplasm. Food and Agriculture Organization of the United Nations. Rome/International Board for Plant Genetic Resources, Rome.