Exposure to ultraviolet-B radiation increases cold hardiness in Rhododendron

The change in the cold hardiness of Rhododendron (cv. English Roseum) following chronic exposure to ultraviolet-B (UV-B) radiation (280–320 nm) was studied. Leaf disks removed from UV-B-exposed plants exbibited a greater tolerance to freezing temperatures than plants that received no UV-B exposure. Visual browning and percent phenolic leakage indicated that UV-B-exposed leaf disks were killed al -11°C. while control disks were killed at -8°C. Ultraviolet-induced production of phenolic compounds may be involved in increasing cold hardiness of Rhododendron leaf tissues.