sUV-B treatment was started just 20 days
after transplantation (DAT) for 3 h dÀ1 at mid-period of the solar noon, till its
maturity up to 100 DAT. Cellulose diacetate and polyester films were used to
transmit UV-B (cut off ca. 292 nm) and exclude UV-B (cut off ca. 318 nm),
respectively, for sUV-B-exposed and unexposed treatments. Filters were replaced
frequently after every week to avoid aging effects on the spectral transmission of
UV-B. The UV-B irradiance at the top of the plant canopy under the lamps was
measured with an ultraviolet intensity meter (UVP Inc., San Gabriel, USA). The
readings were converted to UVBBE values by comparing with the Spectro Power
Meter (Scientech, Boulder, USA). The plants beneath the 0.13-mm-thick cellulose
diacetate film received UVBBE (ambient+1.8 kJ m–2) that mimicked 5% reduction in
stratospheric ozone at Varanasi (291180 ) during clear sky condition on the summer
solstice (Green et al., 1980) normalized at 300 nm wavelength. Plants under
0.13 mm polyester filter lamps received only ambient UV-B (9.6 kJ m–2 UVBBE)
weighted against the generalized plant response action spectrum of Caldwell
(1971). The ozone column thickness was assumed at 3.0 mm, the albedo 0 and the
scatter 1.0.