Published Date: 2006-02-23 23:50:00
Subject: PRO/PL> Phytoplasma, new, potato - USA: 1st report
Archive Number: 20060223.0585
PHYTOPLASMA, NEW, POTATO - USA: FIRST REPORT
A ProMED-mail post
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International Society for Infectious Diseases
Date: 22 Feb 2006
From: ProMED-mail <firstname.lastname@example.org>
Source: American Phytopathological Society, Plant Disease Notes,
March 2006 [edited]
1st 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 
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
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.
(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.
[Keywords: crop, plant disease, potato, chipping disorder, stolbur phytoplasma.
Phytoplasmas are unwalled, prokar
yotes 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.