See:
Greenhouse Plants, Ornamental - Impatiens Necrotic Spot
Symptoms The type of symptoms observed and the intensity of symptom expression will vary depending on the age of the begonia plant when infected and environmental conditions. Plants infected at an early age may be stunted and unthrifty, and flowers of these plants are of poor quality. Plants infected when older may produce normal looking flowers, but foliar symptoms will be present. Rings or zoned spots develop on the leaves of some cultivars or under some conditions. A bright green/dark green chlorotic mottle may be present. Darkened or necrotic veins may occur on undersides of leaves. Brown patches may develop at the petiole end of a leaf.
Note: Excessive light levels may cause virus-like symptoms on Hiemalis begonias.
Reference Daughtrey, M.L., Jones, R.K., Moyer, J.W., Daub, M.E., and Baker, J.R. 1997. Tospoviruses strike the greenhouse industry: INSV has become a major pathogen on flower crops. Plant Disease 81:1220-1230.