XVI International Botanical Congess

Seasonal variations in chlorophyll(chl) a fluorescence (Fv/Fm) and chl levels were studied in azalea and rhododendron cultivars as possible indicators of the physiological status of plants in the field and greenhouse. In late winter there was a decrease in Fv/Fm in leaves of most cvs in the field.In late spring new leaves had low chl levels and, briefly, either high or low Fv/Fm, depending on cv.After placement in a 10C (night temperature)greenhouse at various times during the winter there was a relatively rapid increase in Fv/Fm and a slower increase in chl in all cvs studied. As time in the field increased before the plants went into the greenhouse the time required for flowering and for the rise in chl decreased. Greenhouse temperatures and light intensities were lower than those in the field.