After two weeks, plants in the 2004 experiment were randomly split into two groups with six plants for each cultivar placed on a bench with unpowered UV lamps overhead (no UV), termed the "control" treatment. Another six plants on a bench with identical powered UV lamps overhead were termed the "UV" treatment. Plants were exposed to UV-B soon after reaching the V2 stage (first fully developed trifoliate leaf at the node above the unifoliate node; Fehr and Caviness, 1977). Plants were irradiated for six hours each day, cantered at solar noon from 9:45 -15:45
(local time (LT)) for a total of three days. Measurements were made for three days.
The experimental conditions (temperature, relative humidity (RH), and photoperiod)
were the same as for the growth conditions except for the PPFD, which was
-2 -1 -2 -1 approximately 300 ^moles m s - 400 ^moles m s at seedling height in the control and UV exposure areas. Plants were well-watered throughout the experiment;
there was no evidence of over-watering or water stress on any of the plants.
In the 2007 experiment, two plants per pot, one of Essex and one of Williams
82 and/or Beck's 367NRR, were grown in the control (bank) area. Those to be exposed transferred to the experimental exposure area in a random design when the plants were at R2 (full bloom-an open flower at one of the two uppermost nodes on the main stem with a fully developed leaf) to R4 (full pod elongation-pod
2 cm (3/4 inch) long at one of the four uppermost nodes on the main stem with a fully developed leaf) stage. Twelve pots (eight plants of each cultivar) were in the exposure area while twelve pots were in the control (bank) area. Plants were randomly distributed, both longitudinally and laterally under the UV lamp bank. Measurements were made on the top trifoliate for three days following the initial exposure. The experimental conditions (temperature, RH, PPFD, and photoperiod) were the same as for the growth conditions. Plants were well-watered throughout the experiment: there was no evidence of over-watering or water stress on any of the plants.
In the 2008 experiment, 15 plants, 2 per pot, of Essex were grown in the control (bank) area while 15 plants, 2 per pot, of Essex were grown under the UV lamps. Plants were randomly distributed both longitudinally and laterally, under the UV lamp bank. Experiments were conducted on intact leaves at VC, V1, V2, V3, and V4 stages. Leaf trifoliates of each stage were measured once fully expanded and on subsequent days until the leaves above shaded the trifoliate. The experimental conditions and watering regime were the same as in the 2007 experiment.
The UV-exposure treatment consisted of plants grown under a polyethylene plastic filter that allowed 84% penetration of the UV-Bbe solar radiation, an 87% penetration of UV-A (320 nm - 400 nm) solar radiation, and a 90% penetration of photosynthetically active radiation (PAR) (400 nm - 700 nm). The Llumar plastic allowed below 1% penetration of UV-Bbe solar radiation, 16% penetration of UV-A solar radiation, and an 88% penetration of PAR.
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