February 23, 2006
From: ProMED-mail<promed@promedmail.org>
Source: American Phytopathological Society, Plant Disease Notes, March 2006 [edited] <http://www.apsnet.org/pd/searchnotes/2006/PD-90-0377B.asp>

First report of a defect of processing potatoes in Texas and Nebraska associated with a new phytoplasma
G. A. Secor, Department of Plant Pathology, North Dakota State University, Fargo 58105; I.-M. Lee and K. D. Bottner, Molecular Plant Pathology Laboratory, USDA, ARS, Beltsville, MD 20705; and V. Rivera-Varas and N. C. Gudmestad, Department of Plant Pathology, North Dakota State University, Fargo 58105. Plant Dis. 90:377, 2006; published on-line as DOI: 10.1094/PD-90-0377B. Accepted for publication 11 Dec 2005.

An outbreak of a new potato disease occurred in Texas and Nebraska causing a serious defect in potato chips produced from commercial processing potatoes. The defect consists of patchy brown discoloration of chips and can be a cause for rejection of contracted potatoes by the processor.

Infected potato plants exhibit symptoms of the purple top wilt syndrome, similar to those of the purple top disease in processing potatoes caused by clover proliferation phytoplasma recently [2004] found in Washington and Oregon (3). Foliar symptoms include stunting, chlorosis, slight purple coloration of new growth, swollen nodes, proliferated axillary buds, and aerial tubers. Tuber symptoms include mild vascular discoloration and brown flecking of medullary rays. Seed potatoes from affected plants produce hair sprouts.

Total nucleic acid was extracted from leaf and stolon tissue of symptomatic plants in the field and from tuber samples exhibiting the defect from commercial storages. Nested polymerase chain reactions (PCR) were performed using phytoplasma-universal 16SrDNA-based  primers (P1/P7 and R16F2n/R16R2) (2) to detect the presence of phytoplasmas in these samples. A negative control, devoid of DNA templates in the reaction mix, was included in all PCR assays.

In 2004, 13 foliar samples tested positive for phytoplasmas using PCR. None of the apparently symptomless plants or tubers tested positive. Restriction fragment length polymorphism (RFLP) analysis of the PCR-amplified 16S rDNA using enzymes AluI, MseI, HhaI, BfaI, and Tsp509I indicated that 4 samples are associated with a phytoplasma belonging to subgroup A (16SrI-A) of the "Candidatus Phytoplasma asteris" (aster yellows phytoplasma) group (16SrI), and 9 plant samples were associated with a new phytoplasma related to, but distinct from, the stolbur phytoplasma group (16SrXII). Nucleotide sequence analysis of cloned 16S rDNAs (GenBank Accession Nos. DQ174114-DQ174123) confirmed the results on the basis of RFLP analyses. Sequences of cloned 16S rDNAs were analyzed with previously described phytoplasma strains available in GenBank using DNAStar's (Madison, WI) Lasergene software MegAlign program. The new phytoplasma is only distantly related to the stolbur phytoplasma, sharing 96.6 percent sequence homology.

In 2005, 14 defective tuber samples from storage and 16 symptomatic plants from the field tested positive for the new phytoplasma. In Texas and Nebraska, it appears that at least 2 distinct phytoplasmas seem to be involved in the disease complex contributing to the defects of processed products produced from infected potatoes. Previous reports have suggested a similar defect of chipping potatoes, but the phytoplasma associated with the disease was not identified (1).

To our knowledge, this the 1st report of this new phytoplasma associated with disease and defects of potato and the 1st report of this phytoplasma in the United States.

References:
(1) E. E. Bantarri et al. Trans. ASAE 33:221, 1990.
(2) I.-M. Lee et al. Int. J. Sys. Bacteriol. 48:1153, 1998.
(3) I.-M. Lee et al. Plant Dis. 88:429, 2004.

--
ProMED-mail
<promed@promedmail.org>

[Keywords: crop, plant disease, potato, chipping disorder, stolbur phytoplasma.

Phytoplasmas are unwalled, prokaryotes in the class _Mollicutes_. A new phytoplasma related to potato stolbur
phytoplasma was detected in potato (_Solanum tuberosum_) using PCR samples collected in Texas and Nebraska in 2005. The report is noteworthy because the pathogen causes discoloration of potato tubers that may result in rejection of a shipment for the chipping industry. The main vectors are insects of the leafhopper family (_Macrosteles sp._, _Hyalestes sp._). The disease is found in Central and in southern Europe, as well as the Middle East, the USA, Australia, and Asia. Stolbur is classified as a quarantine parasite in the European Union. Destruction of alternative hosts and the use of certified seed pieces are the main tools to manage these kinds of diseases.

Pictures:
<http://www.eppo.org/QUARANTINE/bacteria/Stolbur/PHYP10_images.htm>

Links:
<http://www.plantdepommedeterre.org/eng/disease/stolbur.htm>
<http://sll.bibul.slu.se/html/sll/eppo/EDS/E-POSBXX.HTM>
- Mod.JAD]

[see also in the archive:
2004
----
Stolbur phytoplasma, potato - Austria: lst report 20040628.1727
Potato purple top disease - USA (WA, OR) 20040415.1041
2001
----
Potato stolbur phytoplasma, potato - Austria 20011124.2877
2000
----
Potato stolbur phytoplasma - Poland: EPPO report 20001127.2063]