New phytoplasma diseases of potatoes
In Bolivia during surveys carried out in 2002/2003, a potato disease called ‘brotes grandes’ (big buds) was found on potato crops in the valleys of Chilón, Saipina, Pulquina and Comarapa (Santa Cruz Department). In some fields, up to 90% of the plants were affected. Symptoms included tuber-like growths in leaf axils, varying in size and colour from red to purple or black and bearing terminal, adventitious leaves. Tubers often produced hair-like shoots, reducing their quality and yield. Molecular analysis revealed the presence of a phytoplasma similar to ash witches’ broom phytoplasma (belonging to subgroup B of the ‘Candidatus Phytoplasma asteris’ group 16SrI). A very similar phytoplasma was also detected in vines (Serjania perulacea, Sapindaceae) present in the vicinity of infected potato fields and showing symptoms of little-leaf (Jones et al., 2005).
In Texas and Nebraska (US), a new disease of potatoes causing a serious defect in transformed potato chips was observed recently. The defect consisted of patchy brown discoloration of chips which may lead to rejection by the processor. In the field, infected potato plants showed stunting, leaf chlorosis, slight purple coloration of new growth, swollen nodes, proliferation of axillary buds and aerial tubers. Tuber symptoms included mild vascular brown discoloration. Seed potatoes from affected plants produced hair-like shoots. Molecular studies done in 2004 revealed the presence of a phytoplasma belonging to the subgroup A of the ‘Candidatus Phytoplasma asteris’ group (16SrI) and of a new phytoplasma related to, but distinct from the stolbur phytoplasma group (16SrXII). In 2005, the new phytoplasma was detected again in 14 defective tuber samples from storage and in 16 symptomatic plants from the field (Secor et al., 2006).
Jones P, Arocha Y, Antesana O, Montellano E, Franco P (2005) ‘Brotes grandes’ (big bud) of potato: a new disease associated with a 16SrI-B subgroup phytoplasma in Bolivia. Plant Pathology 54(2), p 234.
Secor GA, Lee IM, Bottner KD, Rivera-Varas V, Gudmestad NC (2006) First report of a defect of processing potatoes in Texas and Nebraska associated with a new phytoplasma. Plant Disease 90(3), p 377.