2017 ASHS Annual Conference

Intumescence injury has been problematic when plants of susceptible plant species (or cultivars) are grown under light environments deficient in UV-B radiation. The problems are reported in greenhouses covered with glazing materials with low transmission in UV-B range (300-320 nm) of solar radiation as well as indoor environment using electric lighting lacking UV-B. Incidence in greenhouse could be seasonal as the severity of intumescence injury is affected by other factors such as level of global radiation as well as humidity inside the greenhouse. In indoor growing environments, especially when the light spectrum is rich in red (600-700 nm), the problem is consistent and does not allow growing susceptible plants. Our group worked on developing light recipes for suppressing intumescence injury on tomato plants grown under UV-B deficient light environment. UV-B supplementation in greenhouse was reported by a research group at Kansas State University and shown to be an effective solution to prevent the injury. However, this approach has not been examined for indoor growing environment. Furthermore, the minimum dose of UV-B radiation must be found in order to evaluate/modify light environment to grow susceptible species as emitting excessive amounts of UV-B can be harmful for workers as well as plants. In this experiment, we used a tomato rootstock cultivar ‘Beaufort’ (Solanum lycopersicum × S. habrochaites) and grew the seedlings under red and blue LEDs (219 mmol m^-2 s^-1 PPFD) supplemented with varied low doses of UV-B using UV fluorescent lamps (0–7.1 mmol m^-2 d^-1 or 0–2.7 kJ m^-2 d^-1 achieved by 0.33 µmol m^-2 s^-1 or 0.125 W m^-2 UV-B photon flux for 0–6 h). Severity of intumescence injury declined linearly with increasing dose. The linear regression suggested that the minimum dose of UV-B radiation to eliminate the injury was likely around 12-15 mmol m^-2 d^-1, which agreed with our previous observation of the same rootstock seedlings grown under T12-type fluorescent lamps (emitting 15 to 23 mmol m^-2 d^-1 under the conditions previously examined). In contrast, T5-type fluorescent lamps provided only 4.4 mmol m^-2 d^-1 at the PPFD and photoperiod we examined and induced moderate level of intumescence injury over the plants. The results obtained in this experiment can be used as a guideline to examine other susceptible species and cultivars as well as design/evaluate the light environment for these susceptible plants.