UV-B radiation dose requirement for suppressing intumescence injury on tomato plants

Abstract

Intumescence injury is a physiological disorder characterized by watery tumors on a leaf surface associated with abnormal cell enlarge ment and cell division. This problematic intumescence injury has been observed on susceptible cultivars of tomato when grown under an ultraviolet radiation (UV) deficient light environment. In this study, different doses of UV-B radiation were applied after each photoperiod for ‘Beaufort’ interspecific tomato rootstock seedlings (Solanum lycopersicum × S. habrochaites) grown under light emitting diodes (10% blue and 90% red photon flux). The percent number of leaves exhibiting intumescences on leaves decreased linearly with increasing UV-B dose (measured in a 300–320 nm range) in the range examined (0–6.7 mmol m−2 d−1 or 0–2.6 kJ m−2 d−1 achieved by 0.31 μmol m−2 s−1 or 0.12 W m−2 UV-B photon flux for 0–6 h). The severity of intumescence injury was also linearly decreased by increasing UV-B dose. The intumescence incidence as well as severity was the highest in the non-treated control (66.0% leaves showing injury and 2.5–3.8 severity score out of 5) and the lowest (36.1% leaves showing injury and 0.6–1.6 severity score) at the highest dose of 6.7 mmol m−2 d−1 UV-B. The shoot dry weight of seedlings increased by 119% under the highest UV-B dose compared with that of non-treated control. T5-type white fluorescent lamps used for comparison emitted a moderate dose of UV-B (4.3 mmol m−2 d−1 at 0.07 μmol m−2 s−1 for 18 h d−1) and induced a moderate level of intumescent injury. Linear regression suggests that the UV-B dose eliminating intumescence was likely at around 12.3–14.0 mmol m−2 d−1 (4.7–5.3 kJ m−2 d−1), less than a UV-B dose received outdoors on a typical clear summer day. This level of UV-B is achievable under T12-type fluorescent lamps which emit more UV-B and explains why we typically do not see intumescence under T12 fluorescent lighting. The results obtained in this study will help to avoid intumescence in tomato plants grown under controlled environments.