Elimination of Mycoplasmalike Organisms in Cabot Highbush Blueberry with High-Carbon Dioxide Thermotherapy. R. H. Converse, Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. R. A. George, Research Assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Plant Dis. 71:36-38. Accepted for publication 9 September 1986. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. DOI: 10.1094/PD-71-0036.

By means of fluorescent staining with the RNA-specific diamidino phenylindole (DAPI), mycoplasmalike organism (MLO)-related sieve tube fluroescence was detected in longitudinal sections of roots of Cabot highbush blueberry (Vaccinium corymbosum). Attempts to eliminate the MLOs by means of conventional heat therapy of whole plants in a growth chamber were unsuccessful because the plants failed to produce new growth and died within 4 wk when grown at a constant 38 C with ambient CO₂. However, when an enhanced CO₂ level (1,200 ppm) was used, Cabot plants survived at 38 C and produced new shoot growth for 6 wk, enabling softwood cuttings 10—20 mm long to be taken and propagated. After testing for the presence of MLOs with the DAPI staining technique, the number of DAPI-positive plants grown from heat-treated cuttings decreased with time that the source plants had been grown at 38 C, reaching zero at 5 and 6 wk. Stocks of clones of virus-tested, DAPI-negative Cabot (designated Cabot-86) and similarly tested Ivanhoe-86 and Blue Haven-86 highbush blueberry cultivars have now been established.