Aster Yellows Agent Research Articles

Association of phytoplasmas with the decline of European hazel in southern Italy

In the Campania region of southern ltaly. commercial orchards of European hazel (Corylus avellana) are severely affected by yellowing and decline. To determine whether phytoplasmas are associated with the disorder, stem samples from diseased trees were examined using polymerase chain reaction assays. No visible products were obtained by amplification of sample DNA with universal and group‐specific phytoplasma primers. However, when the products obtained with universal primers were re‐amplified with nested primers that were specific for the fruit tree phytoplasmas of the apple proliferation group, most samples tested positively. Restriction site analysis revealed that the trees were infected with the apple proliferation, pear decline, and European stone fruit yellows phytoplasmas in about the same proportion. Some of the trees were doubly infected with one of the fruit tree phytoplasmas and the aster yellows agent. Most of the infected trees were also identified by hybridization of the products obtained in the initial amplification with suitable oligonucleotide probes.

Purification of Aster Yellows Agent from Diseased Lettuce Using Affinity Chromatography

Purification of Aster Yellows Agent from Diseased Lettuce Using Affinity Chromatography

Monoclonal Antibodies Against the Aster Yellows Agent

Hybridoma clones secreting specific monoclonal antibodies against the aster yellows agent, a mycoplasma-like organism, were produced by using partially purified salivary gland preparations from infected leafhopper vectors as the immunogen. After 3947 hybridomas from 20 independent fusions were screened for specific antibody against the aster yellows agent, two table clones were obtained. With these monoclonal antibodies the aster yellows agent in diseased lettuce, periwinkles, and inoculative insects was specifically identified by enzyme-linked immunosorbent assay. The aster yellows agent was serologically differentiated from the mycoplasma-like organisms associated with ash yellows, loofah witches'-broom, paulownia witches'-broom, sweet potato witches'-broom, peanut rosette, maize bushy stunt, and elm phloem necrosis.

Frozen leafhoppers as a vehicle for long-term storage of different isolates of the aster yellows agent

Frozen leafhoppers as a vehicle for long-term storage of different isolates of the aster yellows agent

Delayed expression of aster yellows symptoms in celery

Two strains of aster yellows agent, one resembling a typical 'noncelery-infecting' or eastern type (EAYA) and the other a 'celery-infecting' or western type (CAYA), were compared for their ability to infect celery. Seventy-four percent of the plants inoculated with EAYA and 100% inoculated with CAYA developed symptoms. An average of 115.7 days was required for symptoms of EAY to appear while only 40.6 days were required for CAY. In aster, this difference was much less pronounced. EAYA was less efficiently acquired from celery than was CAYA. The status of this EAYA in the aster yellows complex found in nature is discussed.

The preservation of membranes of tubular bodies associated with mycoplasmalike organisms by tannic acid

Fixation with a mixture of tannic acid and paraformaldehyde–glutaraldehyde resulted in an increased electron density of the membrane structure of tubular bodies that were associated with mycoplasma organisms (MLO) in Vinca rosea plants infected with the Alberta isolate of the aster yellows agent. The tubular bodies, 25.5 ± 4.3 nm in diameter, were bounded with membranes in contrast with the hollow cylinders of 12.3 ± 3.0 nm in conventional fixation. In the study of physical relationships, the tubular bodies were often connected with MLO by a common unit membrane. Some subtubules were formed from a main tubular body.

Occurrence of tubular structures inVinca rosea infected with the Alberta isolate of the aster yellows agent

The association of tubular structures (TS) with mycoplasma-like organisms (MLO) inVinca rosea plants infected with the Alberta isolate of the aster yellows agent was investigated. Studies on graft transmission and infection time course monitored by electron microscopy revealed that MLO were associated with TS in all infection stages examined, viz., from an incubation period to 1 month after symptom development, and that TS were transferable from plant to plant together with MLO by grafting. Intracellular orientation of TS and their relations to MLO were illustrated.

Reduction in the transmissibility of a greenhouse-maintained isolate of aster yellows agent

A celery-infecting isolate of aster yellows agent (isolate A), maintained in the greenhouse since its isolation from the field in 1958, was found to be significantly less transmissible by the aster leafhopper. Macrosteles fascifrons (Stål) than a similar isolate (isolate B) obtained from the same area in 1972. The difference in transmissibility was greatest in male insects, especially those given acquisition access periods as adults. Transmission of isolate A was increased to equal that of isolate B when leafhoppers were injected with inocula prepared from inoculative leafhoppers. No differences were found between isolates in their incubation periods in plants and insects or in their ability to infect asters. On the basis of earlier data and present findings, it is suggested that isolate A has undergone a change in transmissibility during its maintenance in plants grown under artificial conditions.

Effects of Dark Treatment on the Ultrastructure of the Aster Yellows Agent in Situ

Effects of Dark Treatment on the Ultrastructure of the Aster Yellows Agent in Situ

Mycoplasma-like bodies in the salivary glands of insect vectors carrying the aster yellows agent.

Mycoplasma-like bodies in the salivary glands of insect vectors carrying the aster yellows agent.