Rubus Stunt Research Articles

Identification and characterization of the phytoplasma associated with elm yellows in southern Italy and its relatedness to other phytoplasmas of the elm yellows group

SummaryIn the neighbouring regions Basilicata, Campania, and Calabria of southern Italy, diseased trees of European field elm (Ulmus minor) were examined for phytoplasmal infection using polymerase chain reaction (PCR) technology. All affected trees examined tested positively. Using a primer pair specific for the EY phytoplasma group and restriction fragment length polymorphism (RFLP) analysis of PCR‐amplified ribosomal DNA, the organism detected was identified as the elm yellows (EY) phytoplasma. RFLP analysis of PCR‐amplified ribosomal DNA was also employed to attempt differentiation within the EY group which includes, in addition to the EY agent, phytoplasmas infecting Rubus, alder, eucalypts, Spanish broom, and grapevine. Following separate digestion with AluI, RsaI, Sau3AI, MseI, HhaI, and KpnI, all PCR‐products from EY‐group phytoplasmas examined had similar RFLP profiles. When the same ribosomal DNA fragments were digested with TaqI restriction endonuclease, three different restriction profiles were detected among the EY‐group phytoplasmas. These profiles represented, respectively, (1) the EY phytoplasma (2) the phytoplasmas causing rubus stunt and being associated with alder yellows, spartium witches broom, and eucalyptus little leaf, and (3) the flavescence dorée phytoplasma. RFLP analysis using TaqI endonuclease enabled for the first time the differentiation of the phytoplasmas associated with alder yellows, eucalyptus little leaf, and spartium witches broom from the EY agent.

Nature and genetic relatedness of the mycoplasma‐like organism causing rubus stunt in Europe

Cultivated red raspberries (Rubus idaeus), and wild blackberries (R fruticosus, R. caesius, and Rubus hybrids) showing symptoms of rubus stunt were collected in Germany, France, and Italy, Ribosomal DNA of the mycoplasma‐like organism (MLO) that causes rubus stunt was amplified by a polymerase chain reaction procedure and then digested with AtuI and RsaI restriction endonucleases. All samples examined showed the same restriction profiles, which were similar to those of the MLOs inducing elm yellows and alder yellows. However, the rubus stunt MLO could be distinguished from the elm and alder MLOs by Southern blot analysis using DNA probes from a strain of the elm yellows MLO, A variability of the hybridization profiles, probably caused by restriction fragment length polymorphisms, was observed among the rubus stunt samples. From both rDNA restriction site and Southern blot analyses it can be concluded that the rubus stunt agent and the elm yellows and alder yellows MLOs are not identical but closely related and can be grouped in the same taxonomic cluster.

In Vitro Micropropagation for Maintenance of Mycoplasma-like Organisms in Infected Plant Tissues

A collection of mycoplasma-like organisms (MLOs) was maintained in plant tissues micropropagated in vitro. MLO-infected plants included Chrysanthemum frutescens L. with chyrsanthemum yellows disease, Gladiolus sp. L. with “germ fins,” Hydrangea macrophilla (Thunb.) DC. with virescence, Rubus fruticosus L. with rubus stunt, and periwinkle [Catharanthus roseus (L.) G. Don] singly infected by the following MLOs: Italian periwinkle virescence, chrysanthemum yellows, North American aster yellows, Italian periwinkle stunt, American periwinkle little leaf. Shoots micropropagated in vitro exhibited symptoms of little-leaf and/or abnormal proliferation of axillary shoots resulting in “witches' broom” appearance that resembled symptoms in grafttransmitted greenhouse-grown or naturally infected field-collected plants. These symptoms, typical of infection by MLOs, were not observed in micropropagated healthy shoots of the same plant species, and, compared with the healthy ones, varied with MLO strain and host plant species. Dot hybridizations with a nonradioactive cloned DNA probe provided evidence for the presence of MLOs in propagated tissues through serial subcultures.

Mycoplasma‐like bodies associated with Rubus stunt disease

SUMMARYMycoplasma‐like bodies were found by electron microscopy in the sieve tubes of blackberry, loganberry and raspberry plants showing symptoms of Rubus stunt disease, but not in those of normal plants. Watering diseased blackberry plants with aureomycin caused remission of the symptoms and greatly decreased the number of mycoplasma‐like bodies.

Rubus stunt, a leafhopper-borne virusdisease

Rubus stunt, a leafhopper-borne virusdisease