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Title: Molecular detection and identification of group 16SrI and 16SrXII phytoplasmas associated with diseased potatoes in Russia

item Bottner, Kristi
item Owens, Robert
item Lee, Ing Ming

Submitted to: Plant Disease
Publication Type: Research Notes
Publication Acceptance Date: 1/31/2008
Publication Date: 4/1/2008
Citation: Girsova, N., Bottner, K.D., Mozhaeva, K.A., Kastalyeva, T.B., Owens, R.A., Lee, I. 2008. Molecular detection and identification of group 16SrI and 16SrXII phytoplasmas associated with diseased potatoes in Russia. Plant Disease. 92:654.

Interpretive Summary: Phytoplasma are very small bacteria that lack a cell wall and that cause several hundred economically important diseases in plants worldwide. Potato purple top and similar diseases have caused tremendous damage to potato tuber production in South America, Mexico, the US, and elsewhere in the world. Most of these diseases are caused by phytoplasmas. Diseased potato exhibiting discoloration symptoms similar to those of purple top have been reported in several potato growing regions in Russia. Previous studies based on symptoms and other biological criteria, including insect vector relationships, strongly suggested these diseases may be caused by phytoplasmas. However, the causal agents associated with the diseases had not been confirmed prior to the present study. In collaboration with Russian scientists, we have conducted preliminary surveys of affected plants, and through the use of molecular tools, have discovered that at least two phytoplasma strain groups, those of stolbur and aster yellows phytoplasmas, were associated with these diseases. Stolbur phytoplasma is the major pathogen associated with purple top disease of potato in Russia. The information will aid implementation of quarantine regulation, since the stolbur phytoplasma is under quarantine regulation in the U.S. The information will also help extension workers and plant diagnosticians in Russia to determine how to combat the disease.

Technical Abstract: Phytoplasmal diseases have long been suspected to occur in several potato growing regions in Russia. Symptoms resembling those of stolbur disease are most prevalent. Possible phytoplasmal etiologies of these diseases have never been verified by molecular means. During the summer of 2006, 33 potato plants exhibiting symptoms including purple top, round leaves, and stolbur-like symptoms characterized by purple top, stunting, bud proliferation, and formation of aerial tubers, were randomly collected from the Volga River Region, Central Region and Northern Caucasian Region in Russia. DNA extracts were prepared from these samples and a nested PCR amplification using primer pair P1/P7 followed by primer pair R16F2n/R16R2n was performed to detect phytoplasmas in infected potato samples. Eight out of 33 potato samples tested positive in the first PCR. Twelve out of 33 potato samples tested positive in nested PCR. The majority of potato samples that tested positive for phytoplasma exhibited stolbur-like symptoms. Restriction fragment length polymorphism (RFLP) analysis of nested PCR products (1.2 kb 16S rDNA fragments) was performed. PCR products (6 µl) were digested singly with the restriction enzymes AluI, HaeIII, HhaI, HpaII, KpnI, MseI, RsaI, and Tsp509I. Comparison of RFLP profiles with published profiles was used for identification of the putative phytoplasmas detected. Among the 12 PCR positive potato samples, ten yielded RFLP profiles very similar or identical to those characterizing stolbur phytoplasma, a member of group (16SrXII), subgroup 16SrXII-A, and two yielded RFLP profiles similar to those of aster yellows phytoplasma group 16SrI). Nucleotide sequence analysis of cloned 16S rDNA confirmed the results of the RFLP analyses and also indicated that the two samples yielding 16SrI profiles were doubly infected with two phytoplasma strains belonging to subgroups 16SrI-A and 16SrI-B. The results demonstrated that stolbur phytoplasma is prevalent in several potato growing regions of Russia. This is the first confirmation by molecular procedures that stolbur phytoplasma (16SrXII-A) is prevalent in several potato growing regions and is the first report of 16SrI-A and 16SrI-B phytoplasmas in diseased potatoes in Russia.