Large-scale Screening for X-disease Phytoplasma Infection in Chokecherry

Abstract

Chokecherry (Prunus virginiana L.) germplasm collected from North Dakota, South Dakota, and Minnesota and established in Bismarck, N.Dak. was screened for infection by the X-disease phytoplasma and for putative X-disease-resistant plants. A total of 1792 chokecherry trees were first screened by observation of characteristic disease symptoms and were given a visual disease rating. In 1996, 97% of the trees were severely diseased, or rated 3 or lower on a 5-point scale. The remaining 3% (55 trees) showed vigorous growth and had few or no X-disease symptoms, and were rated 4 or 5. Of these trees, 44 (80%) were found to contain the X-disease phytoplasma as indicated by reactions with a monoclonal antibody that is specific for this phytoplasma. The other 11 trees (20%) were then found to contain the X-disease phytoplasma using the highly sensitive, but more expensive and time-consuming, nested-polymerase chain reaction (PCR). Employment of a combination of visual screening, monoclonal antibody assay, and nested-PCR provided an effective and efficient means for examining a large number of plant materials for infection by the phytoplasma. The chokecherry trees that were infected but had few or no X-disease symptoms were considered to be resistant/tolerant to X-disease.