Effects of UVB Light On Edema and Intumescence Development

Intumescence and edema development are physiological disorders that are often referred to interchangeably and primarily affect plant leaves.  When damage is severe, economic loss results from reduced aesthetic value or yield losses correlated with reduced photosynthetic area.  We evaluated whether UVB light affects the incidence and severity of these disorders on ivy geranium (Pelargonium peltatum L’Herr ex. Ait.) ‘Amethyst’, ‘Lambada’, and ‘Sybil Holmes’ and tomato (Solanum lycopersicum L. var. hirsutum ‘Maxifort’ and var. esculentum ‘Trust’) in separate greenhouse experiments for each genus.  UVB-emitting fluorescent light bulbs were mounted over plants without (+ UVB-light) and with (- UVB-light) UV-absorbing polyethylene.  Numbers of leaves affected by the disorders were counted twice weekly.  Dissection and scanning electron microscopy (SEM) was performed on fresh samples.  Edema development on ivy geranium occurred uniformly in the +/-  UVB-light treatments.  Intumescence development on tomato var. esculentum did not occur in either UVB-light treatment, but it was different across treatments on tomato var. hirsutum:  + UVB-light resulted in 6% of leaves and 1% of leaflets affected whereas – UVB-light resulted in 30% of leaves and 12% of leaflets affected.  Dissecting and SEM showed clearly that a single edemata is comprised of hundreds of cells that swell as one unit and then collapse whereas intumescences are comprised of groups of individual cells that grow individually to the point of bursting.  The disorders are distinctly different and caused by different phenomena.