Aster yellows phytoplasma identified in scentless chamomile by microscopical examinations and molecular characterization

Scentless chamomile (Matricaria perforata Merat) plants were commonly found infected with a yellows-type disease caused by phytoplasma in several fiel ds in Alberta, Canada. Typical phytoplasmas were detected in the phloem cel ls in ultrathin sections from leaf, stem, root and flower petiole tissues e xamined by electron microscopy. Application of 4'6-diamidino-2-phenylindole -2HCl (DAPI) staining techniques confirmed the presence of the phytoplasma in these tissues. These observations were supported by polymerase chain rea ction (PCR) assays, using two primer pairs, P1/P6 and R16(1)F1/R1, derived from phytoplasma rDNA sequences. Aster yellows and potato witches'-broom (P WB) DNA phytoplasma samples served as positive controls and were used to st udy group relatedness. In a direct PCR assay, DNA amplification with univer sal primer pair P1/P6 gave the expected PCR products of 1.5 kb. Based on a nested-PCR assay using the latter PCR products, as templates, and a specifi c primer pair R16(1)F1/R1 designed on the basis of AY phytoplasma rDNA sequ ences, a PCR product of 1.1 kb was obtained from each phytoplasma-infected chamomile and AY samples but not from PWB phytoplasma and healthy chamomile controls. DNA amplification with specific primer pair R16(1)F1/R1 and rest riction fragment length polymorphism indicated the presence of AY phytoplas ma in the infected scentless chamomile sample.