Tropical regions receive the highest level of global solar ultraviolet (UV) radiation especially UV-B (280-320 nm).The average daily dose of the UV-B radiation in Madurai, South India (10 ~ N) is 10 kJ m -2. This is approximately 50% more than the average daily UV-B radiation in many European countries. A field study was conducted using selective filters to remove either the UV-B (< 320 nm) or UV-B/A (<400 rim) of the solar spectrum, and the effects were followed in Cyamopsis tetragonoloba, Vigna mungo, and Vigna radiata to determine their sensitivity to UV. When compared to ambient radiation, exclusion of solar UV-B increased the seedling height, leaf area, fresh weight and dry weight and the crop yield by 50% in the case of Cyamopsis, and the extent of such increase was slightly less under UV-B/A exclusion. In V. mungo a significant reduction was seen in solar UV excluded plants while V. radiata was found to be unaffected.

We investigated the effects of UV-A and UV-B enhanced radiation on plants of Phaseolus mungo. Low doses caused varying responses in such growth and yield components as shoot and root lengths, leaf area, fresh mass and dry matter, pod numbers, and seed numbers and weights. Compared with the performances of the control plants, supplementation with UV-A radiation promoted overall growth, while UV-B radiation inhibited development. Moreover, both sources of radiation caused reduced yields, although this effect was comparatively less in plants treated with UV-A radiation.

The effect of low doses of UV-A (320-400 nm) and UV-B (280-320 nm) radiation on photosynthetic activities in Phaseolus mungo L was investigated under field condition. Supplementation of UV-A enhanced the synthesis of chlorophyll and carotenoids than the UV-B supplemented plants. Significant increase was seen in the concentration of UV-B absorbing compounds of UV-B treated plants. Increase of PS 2 activity in UV-A treated plants was seen. Changes in photosynthetic activity were measured in terms of PS 2 mediated 02 evolution and Chl a fluorescence.

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