An electron microscope (EM) assay able to detect pineapple closterovirus (PCV) from samples equivalent to less than lmg leaf tissue was developed and used to identify pineapple leaf materials having high PCV level. The latter was then purified at concentrations never achieved before. We started to produce monoclonal antibodies to PCV using partially purified virus. From about 300 cell lines, 38 were found to be promising. Six of them were selected for cloning. Four clones were selected for production of ascites. One of the monoclonal antibodies was found to decorate PCV. Recently, using partially purified virus samples in EM studies, a badnavirus from pineapple samples was found. This virus (PBV) has been amplified in PCR tests. The PBV may be important to mealybug-wilt etiology and will be part of continuing investigation. - Previously, it had been shown that crowns treated at 50°C or 60°C exhibited increased vigor and yield but also displayed serious damage. Our results showed that pretreatment at 30°C allowed later treatments at 50°C with significantly reduced damage. This experiment was repeated with similar results. Thermotolerance stimulated by pretreatment at 30 to 40°C peaks approximately 7 hours after pretreatment and remains active for at least 24 hours. We have begun to determine the impact of these treatments on pineapple growth and yield, and on the PCV and PBV.