Intraspecific variation in sensitivity of high yielding rice varieties towards UV-B radiation.

Effective screening of thirteen commonly cultivated rice (Oryza sativa L.) varieties was carried out to evaluate the varietal-specific differences in morphological, physiological and biochemical responses to various doses of UV-B irradiation (7, 14, 21 and 28 kJ m-2d-1). Determination of UV-B tolerant rice varieties would be helpful in selecting a suitable variety for the areas experiencing higher influx of UV-B radiation. Based on the initial screening of thirteen rice varieties, carried out by analyzing shoot length, fresh weight, photosynthetic pigments and the rate of lipid peroxidation under various doses of UV-B, it was found that Mangalamahsuri, Aathira, Kanchana, Jyothi and Annapoorna were tolerant lines and Neeraja, Swetha, Swarnaprabha and Aiswarya were the sensitive ones. Further screening of these nine varieties was done by analyzing primary metabolites (total protein, soluble sugar and proline content) and non enzymatic antioxidants (ascorbate and glutathione) involved in free radical scavenging mechanism to mitigate the negative effects of UV-B irradiation. Based on the cumulative stress response index (CSRI), the sum of relative individual component responses (total protein, soluble sugar, proline, ascorbate and glutathione content) at each UV-B treatment and total stress response index (TSRI), the sum of CSRI of all the four UV-B treatments for each variety, nine rice varieties selected after primary screening were classified as tolerant (Mangalamahsuri, Aathira and Kanchana), intermediate (Jyothi, Annapoorna, Neeraja and Swetha) and sensitive (Swarnaprabha and Aiswarya).