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Title: CLOVER PROLIFERATION GROUP (16SRVI), SUBGROUP A (16SRVI-A) PHYTOPLASMA IS PROBABLE CAUSAL AGENT OF DRY BEAN PHYLLODY DISEASE IN WASHINGTON

Author
item Lee, Ing Ming
item Bottner, Kristi
item Miklas, Phillip - Phil
item Pastor Corrales, Marcial

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2004
Publication Date: 4/8/2004
Citation: Lee, I., Bottner, K.D., Miklas, P.N., Pastor Corrales, M.A. 2004. Clover proliferation group (16srvi), subgroup a (16srvi-a) phytoplasma is probable causal agent of dry bean phyllody disease in washington. Plant Disease. 88:429.

Interpretive Summary: Phytoplasmas are very small bacteria that lack a cell wall and that cause economically important diseases in more than 300 plant species worldwide. The list is growing rapidly; many new emerging and previously unknown diseases have been identified since reliable molecular tools, developed by our laboratory (Molecular Plant Pathology Laboratory) and other research groups, became available in the last decade. In this paper we reported a new phytoplasmal disease, termed dry bean phyllody, causing sterility (aborted seed pods) of dry beans grown in Washington. The disease has caused great reduction in the production of several dry bean cultivars. This is the first report of dry bean phyllody disease in the United States. The information in this paper will aid implementation of quarantine regulations, and it will help extension workers and plant diagnosticians to determine how to combat this new disease.

Technical Abstract: A new disease, dry bean phyllody, was observed in the Columbia Basin region of Washington in 2003 in dry bean (Phaseolus vulgaris L.) cultivars of Andean origin grown in Mattawa and Paterson, WA, causing great reduction in dry bean production in infected plants. Symptoms of dry bean phyllody (DBPh) became apparent during mid to late pod development and were characterized by formation of leafy petals (phyllody) and aborted seed pods that appeared as thin, twisted, and corrugated leaf-like structures. Deformed-sterile pods that were small, sickle-shaped, upright, and leathery were also observed. The infected plants generally exhibited chlorosis and stunting and bud proliferation may also occur from leaf axils. Symptoms of DBPh were indicative of possible infection by phytoplasmas. A nested PCR assay was used to detect phytoplasmas present in the diseased dry bean plants. RFLP and phylogenetic analyses of amplified 16S rDNA sequences were employed for phytoplasma identification. All four symptomatic bean samples collected were positive for phytoplasma infection. RFLP analyses of 16S rDNA sequences with restriction enzymes, MseI, AluI, HhaI, RsaI, and HpaII indicated that the phytoplasma strains associated with dry bean phyllody belonged to the clover proliferation group (16SrVI), subgroup A (16SrVI-A). The taxonomic affiliations of the DBPh phytoplasma strains were confirmed by phylogenetic analysis of cloned 16S rRNA gene sequences (GenBank accession nos.: DBPh2, AY496002; DBPh3, AY496003). The 16S rDNA sequences of the DBPh strains were most closely related to subgroup 16SrVI-A phytoplasma strains, VR (with 99.7% sequence homology) and CP (with 99.2% homology). The etiological role of 16SrVI-A phytoplasma strains in DBPh disease was confirmed by a modified test of Koch's postulates. Infected tissue from one phytoplasma-positive dry bean sample was grafted onto three Pinto UI-114 bean seedlings in the greenhouse. Within sixty days after grafting, the bean seedlings developed symptoms similar to the original diseased samples. The transmitted phytoplasma was detected in each of the grafted symptomatic seedlings, and the RFLP patterns of its 16S rRNA gene sequences were identical to those of the phytoplasmas in the scions. The results on DBPh provide the first confirmed case of this disease in the U.S. and the first evidence that DBPh may be caused by phytoplasma.