November 23, 2004
Source: British Soc. Plant Pathol., New Disease Reports, Vol. 10 [edited]

Brotes grandes (big bud) of potato: a new disease associated with a 16SrI-B subgroup phytoplasma in Bolivia
P. Jones, Plant-Pathogen Interactions Division, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK; Y. Arocha, National Centre for Animal and Plant Health (CENSA), Apdo 10, San Jose de Las Lajas, Havana, Cuba; O. Antezana, Ladiplantas Community Plant Clinic, Comarapa, Bolivia; E. Montellano (as for Antezana); and P. Franco CIAT, Santa Cruz, Bolivia. Accepted for publication 05/11/04

Potatoes are the main crop of smallholder farmers in the Valles crucenos, Santa Cruz Province, Bolivia. During surveys carried out from 2000 to 2003, a disease locally known as brotes grandes ('big bud'), was prevalent on
crops in the valleys of Chilon, Saipina, Pulquina and Comarapa, where up to 90 percent of plants were affected in some fields.

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.

Previously, this syndrome was presumed to be rhizoctoniosis, caused by basal stem infection by _Rhizoctonia solani_, but _R. solani_ was absent from all diseased plants examined in the present study.

As other potato diseases similar to brotes grandes (BG) have been attributed to phytoplasmas in Australia (Harding & Teakle, 1993), Poland (Hamilton, 2000), Canada (Khadhair et al, 2003) and Mexico (Martinez-Soriano et al, 1999), tissues from Bolivian plants were indexed by nested PCR (nPCR) using phytoplasma universal rRNA primer pairs P1/P7 and R16F2n/R16R2.

nPCR products resulting from 43/50 BG samples and digested separately with HaeIII, RsaI or AluI endonuclease all produced identical RFLP profiles. RFLP profiles of nPCR products amplified from 3 samples of an unidentified vine with little-leaf symptoms in hedgerows surrounding potato fields in La Tranca, Santa Cruz Province, were indistinguishable from BG profiles. 16S rDNA sequences derived from PCR products shared 99 percent sequence homology among BG phytoplasmas.

Sequences from the phytoplasmas obtained from potato (Accession No. AY725209) and from the unknown vine (Accession No. AY725210) were each most similar (98 percent) to that of ash witches' broom phytoplasma (Accession number AY568302).

This is the 1st report of a phytoplasma of the Aster yellows (16SrI) group associated with a potato disease in Bolivia.

References

Hamilton D, 2000. Potato Stolbur Phytoplasma in Poland. European and Mediterranean Plant Protection Organisation (EPPO) report (04).

Harding RM, Teakle DS, 1993. Potato purple top wilt in Queensland. In: Raychaudhuri SP and Teakle DS, eds. Management of plant diseases caused by fastidious prokaryotes. New Delhi, India: Associated Publishing Co., 14-20.

Khadhair A, Duplessis H, McAlister P, Ampong-Nyarko K, Bains P, 2003. Transmission and characterization of phytoplasma diseases associated with infected potato cultivars in Alberta. Acta Horticulturae 619,167-176.

Martinez-Soriano JP, Leyva-Lopez NE, Zavala-Soto ME, Beres M, Leal-Klevezas DS, 1999. Deteccion molecular del agente causal del sindrome "bola de hilo" de la papa en semillas infectadas y asintomaticas. Biotecnologia Aplicada 16, 93-96.

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[Potato stolbur [PS] (a.k.a. Tomato stolbur) is one of a group of phytoplasmas causing yellows-type diseases in Europe within the broad concept of European aster yellows (Cousin & Smith, 1988; EPPO/CABI, 1996). Parastolbur and metastolbur are strains of stolbur; northern stolbur is probably caused by potato witches' broom phytoplasma (EPPO/CABI, 1996), pseudoclassic stolbur is poorly defined, and pseudostolbur is a physiological disorder (Valenta et al., 1961).

A little leaf disease of tomatoes, _Capsicum_, and eggplants in southeastern France has been attributed to a phytoplasma distinct from stolbur (Marchoux & Rougier, 1987). Tomato big bud phytoplasma, reported mainly from regions outside the EPPO region, causes a similar disease and some taxonomists regard them as synonymous. PS infects 45 species in the _Solanaceae_; principal hosts are potato, tomato, peppers and eggplant. Of concern to plant pathologists are infected plants species in the _Asteraceae_, _Convolvulus arevensis_ and _Fabaceae_ (_Trifolium_ spp.) that are sources of inoculum. PS occurs in 15 countries of the EPPO region, Asia (8 countries) and the EU. The most important vector in eastern Europe is _Hyalesthes obsoletus_, but there are several others that are of concern.

Local spread in a field appears to originate from infected weed species rather than from crops. PS can be detected using specific stains in infected tissues, by indirect immunofluorescence, and by a tissue blot technique.

Links:
<http://www.bspp.org.uk/ndr/jan2005/2004-66.asp>
<http://www.eppo.org/QUARANTINE/bacteria/Stolbur/PHYP10_ds.pdf>
- Mod.DH]