March 16, 2005
Source: American Phytopathological Society, Plant Disease Notes [edited]

First report of barley as host of a phytoplasma belonging to group 16SrI, subgroup B, and ribosomal protein subgroup rpI-B in Lithuania
L. Urbanaviciene and R. Jomantiene, Fitovirus Laboratory, Institute of Botany, LT-08406 Vilnius, Lithuania; and R. E. Davis, Molecular Plant Pathology Laboratory, USDA-Agricultural Research Service, Beltsville, MD 20705. Plant Dis. 89:339, 2005; published on-line as DOI: 10.1094/PD-89-0339A. Accepted for publication 2 Dec 2004.

Numerous diseased plants of barley (_Hordeum vulgaris_ L.) exhibiting twisted, abnormally thin and yellowed awns, reduced spikelets, and general stunting and yellowing were observed in fields in the Vilnius and Kaisiadorys regions of Lithuania. The possible association of a phytoplasma with the disease, termed barley deformation (BaDef), was assessed using polymerase chain reaction (PCR).

3 phytoplasma universal primer pairs (P1/P7, R16F2n/R16R2, and rpF1/rpR1) (1,2,4) were employed to amplify ribosomal (r) RNA gene (rDNA) and ribosomal protein (rp) gene sequences. Template DNA extractions and PCR (direct and nested) were conducted as previously described (4). Although DNA was amplified in PCRs containing template extracted from diseased plants, no amplification was observed in PCRs containing DNA from symptomless plants sampled from the same fields.

The BaDef phytoplasma was identified and classified according to Lee et al. (4) through restriction fragment length polymorphism (RFLP) analysis of 1.2-kbp 16S rDNA amplified in the PCR primed by primer pair R16F2n/R16R2 and analysis of the 1.2-kbp rp gene sequences amplified in PCR primed by primer pair rpF1/rpR1. On the basis of collective RFLP patterns of amplified 16S rDNA and rp gene sequences,
the BaDef phytoplasma was classified as a member of group 16SrI (group I, aster yellows phytoplasma group), subgroup B (16SrI-B), and rp subgroup rpI-B.

Ribosomal protein subgroup B was distinguished from other rp subgroups on the basis of the presence of a recognition site for HpaII. The 1.8-kbp rDNA product of PCR primed by P1/P7 and the 1.2-kbp rpF1/rpR1 PCR product were cloned and sequenced, and the sequences were deposited in GenBank under Accession No. AY734453 for the BaDef 16S rDNA and Accession No. AY735448 for the BaDef rp gene sequence.

Previously, only oat proliferation (OatP) phytoplasma, a member of subgroup 16SrI-A, had been characterized in a cereal crop (_Avena sativa_ L.) in Europe (3); BaDef is another phytoplasmal disease threatening cereal crops in the region.

References:
(1) S. Deng and D. Hiruki. J. Microbiol. Methods 14:53, 1991.
(2) D. E. Gundersen and I. M. Lee. Phytopathol. Mediterr. 35:144, 1996.
(3) R. Jomantiene et al. Plant Dis. 86:443, 2002.
(4) I. M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998.

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[Aster yellows (AY) is the most widespread plant disease among those known to be caused by phytoplasmas. AY phytoplasmas are associated with diseases in more than 100 plant species worldwide, predominantly in herbaceous dicotyledonous plants. In North America, AY diseases are attributed primarily to phytoplasma strains belonging to subgroups 16SrI-A (termed Eastern AY phytoplasma) and 16SrI-B (termed California AY or Western AY phytoplasma) in the AY group (16SrI). Both 16SrI-A and 16SrI-B phytoplasmas are transmitted by a variety of
polyphagous leafhopper species and have a wide range of plant hosts. On the basis of RFLP patterns of the 16S rDNA, the OatP phytoplasma was classified as a member of group 16SrI (group I, aster yellows phytoplasma group). The RFLP patterns of the 16S rDNA were indistinguishable from those of 16S rDNA from tomato big bud (BB) phytoplasma and other phytoplasmas classified in group I, subgroup A (subgroup I-A, tomato big bud phytoplasma subgroup). Disease management depends upon the crop involved. Monitoring of leafhoppers and early detection of AY yellows symptoms are important for those crops in which hand-removal of diseased plants is feasible. For field crops, there are very few management options available. Crop rotation will not reduce aster yellows, because it is not a soil-borne disease, and most crops are susceptible to the phytoplasma. There are no fungicides available to control aster yellows. I rather doubt that there are varieties that possess resistance to the AY phytoplasma.

Links:
<http://www.apsnet.org/phyto/abstract/2003/pno03ab.htm>
<http://www.agr.gov.sk.ca/DOCS/crops/integrated_pest_management/disease/asteryellows01.asp>
- Mod.DH]