Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 27, 2001
Publication Date: N/A
Interpretive Summary: In Oregon, plants of black raspberry are sometimes affected by a severe disease called black raspberry witches' broom (BRWB) disease, but the cause of the disease had not been precisely identified. In work to gain information about what may be causing the disease, which often kills affected plants, we found that a phytoplasma (small bacterium-like organism) was associated with the disease. By studying the DNA of the BRWB phytoplasma, we found that it is related to the phytoplasmas that cause yellow edge disease in clover and X-disease in peach trees, but the BRWB phytoplasma differed from those and all other phytoplasmas that had been described previously. Our findings contribute knowledge about the biological diversity of phytoplasmas and provide information that will be useful to scientists and diagnosticians for further study of BRWB disease.
Plants of Rubus occidentalis (black raspberry) Munger' exhibiting symptoms of black raspberry witches' broom (BRWB) disease were observed in commercial fields in Oregon (1). Symptoms were often severe, leading to death of infected plants, and a phytoplasma (mycoplasmalike bodies) was observed in ultrathin sections of diseased plants (1). In the current work, the association of phytoplasma with BRWB was assessed using the polymerase chain reaction (PCR) for amplification of phytoplasmal rDNA. 16S rDNA was amplified in PCR primed by primer pair P1/P7 and reamplified in nested PCR primed by primer pair R16F2n/R2 (F2n/R2) by a method described previously (2). These results indicated the association of a phytoplasma, designated BRWB phytoplasma, with the disease. Identification of BRWB phytoplasma was accomplished by restriction fragment length polymorphism (RFLP) analysis of DNA amplified in PCR primed by F2n/R2. Phytoplasma classification was done according to the system of Lee et al. (3). On the basis of collective RFLP patterns of the amplified 16S rDNA, the BRWB phytoplasma was classified as a member of group 16SrIII (group III, X-disease phytoplasma group). The HhaI RFLP pattern of BRWB 16S rDNA differed from that of its close relative, clover yellow edge (CYE) phytoplasma. The RsaI RFLP pattern of BRWB rDNA differed from that of rDNA from all phytoplasmas previously described in group III. Based on these results, BRWB phytoplasma was classified in a new subgroup, designated subgroup Q (III-Q) within group III. The 1.8 kbp DNA product of PCR primed by primer pair P1/P7 was cloned and its nucleotide sequence determined. The sequence was deposited in GenBank under Accession no. AF301841.