Disease resistance and growth responses in Pelargonium × hortorum plants to brief pulses of UV-C irradiation

Abstract

Data collected from the current experiments showed that brief pulses of UV-C irradiation (i.e. 0.5–10.0kJm−2) on Pelargonium×hortorum L.H. Bail (zonal geraniums) plants of cvs ‘Victor’ and ‘Glacis’ significantly (P<0.05) reduced Botrytis cinerea infection. This inducible defence response peaked 24h post UV-C treatment and caused 47% reduction in lesion diameters after artificial inoculation with B. cinerea. All UV-C doses applied on both geranium cultivars were significantly (P<0.05) effective and the lower-most effective dose, 2.5kJm−2 was suggested for future and possible commercial use. Between the two cultivars tested, cv ‘Victor’ responded better against B. cinerea infection, while cv ‘Glacis’ displayed specific morphological changes associated with growth and flowering. Irradiated cv ‘Glacis’ plants showed significantly (P<0.05) higher number of inflorescences, number of leaves and plant heights compared to the non-irradiated controls. For the first time, the effects of brief pulses of UV-C irradiation on photosynthetic activity of ornamental plants were tested. A significant (P<0.05) rise in CO2 assimilation (As), stomatal conductance (gs) and transpiration (E) was recorded immediately after UV-C irradiation. However, this increase was only temporary as As, gs and E values returned to normal (i.e. at control levels) within the next 24h. We suggest that brief pulses of UV-C on geranium plants may facilitate growth and development by inducing photomorphogenic responses.